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+*** START OF THE PROJECT GUTENBERG EBOOK 59611 ***
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+Transcriber Note
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+Text emphasis denoted as _Italic_ and =Small Caps=.
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+                                  THE
+
+                          JOURNAL OF GEOLOGY
+
+
+                       _JANUARY-FEBRUARY, 1893._
+
+
+                   *       *       *       *       *
+
+
+            ON THE PRE-CAMBRIAN ROCKS OF THE BRITISH ISLES.
+
+
+During the last twenty years much has been written about the
+"pre-Cambrian" rocks of the British Isles. Unfortunately when attention
+began to be sedulously given to the study of these ancient formations,
+the problems of metamorphism were still a hundred fold more obscure
+than they have since become; the aid of the microscope had not been
+seriously and systematically adopted for the investigation of the
+crystalline schists, and geologists generally were still under the
+belief that the broad structure of these schists could be treated like
+those of the sedimentary rocks, and be determined by rapid traverses of
+the ground. We have now painfully discovered that these older methods
+of observation were extremely crude, and that the work performed in
+accordance with them is now of little interest or value save as a
+historical warning to future generations of geologists. Geological
+literature has meanwhile been burdened with numerous contributions
+which remain as a permanent incubus on our library shelves.
+
+It may serve a useful purpose at the present time in possibly aiding
+those who are engaged in the study of the oldest rocks of North
+America, if I place before them, as briefly as possible, the main facts
+which in my opinion have now been satisfactorily proved regarding the
+corresponding rocks of Britain, and if I indicate at the same time some
+of the more probable inferences in those cases where the facts, at
+present known, do not warrant a definite conclusion.
+
+It is obvious that in any effort to establish that a group of rocks is
+older than the very base of the sedimentary fossiliferous formations,
+we must somewhere find that group emerging from under the bottom of
+these formations. Until lithological characters are ascertained to be
+so distinctive and constant as to be comparable to fossil evidence
+for purposes of stratigraphical identification, we should not assume
+that detached areas of older rocks rising amid Palæozoic, Secondary or
+Tertiary formations are pre-Cambrian. We should, if possible, begin
+at the bottom of the Palæozoic systems and work backward, tracing
+each successive system or group as these rise from under each other,
+until we arrive at what appears to be the oldest traceable within
+the region of observation. It is clear that in the present state of
+knowledge we have no satisfactory means of identifying such successive
+systems in widely separated countries. All that can be attempted in
+the meantime is to ascertain the special types in each region, and to
+point out their general resemblances or contrasts to those of other
+regions. It is better to avoid confusion by refraining from applying
+the stratigraphical names adopted for the oldest rocks of one region
+to those of another geographically remote, though we may hope that
+eventually it may be possible to work out the equivalence of these
+local names.
+
+In the British Isles, by much the most important region for the study
+of the oldest rocks is to be found in the north-west Highlands of
+Scotland. The very basement strata of the Cambrian system are there
+traceable for a distance of more than 100 miles, reposing with a
+strong unconformability upon all rocks of older date. They consist
+of dolomitic shales with _Olenellus_, resting upon a thick group of
+quartzites, full of annelid tubes. One of the most remarkable features
+of these ancient strata is the persistence of their component bands
+or zones which, though sometimes only a few feet thick, can be traced
+throughout the whole tract of country just referred to. For the study
+of the pre-Cambrian rocks this is an important point, for we can be
+quite certain that even where fossil evidence locally fails, the same
+basement members of the Cambrian system are persistent and lie directly
+upon the pre-Cambrian series.
+
+_Lewisian Gneiss._ Ever since the researches of Murchison and Nicol in
+the north-west of Scotland, it has been known that two distinct systems
+of rock underlie the quartzites to which I have just alluded. Murchison
+regarded the upper of these as of Cambrian age, while he assigned the
+unconformable quartzites and limestones above it to the Lower Silurian
+period. But the recent discovery of the _Olenellus_ zone intercalated
+conformably between the quartzites and the overlying limestones may be
+regarded as proving that all the rocks which underlie the quartzites
+and are separated from them by a strong unconformability must be
+pre-Cambrian. It is thus established beyond any reasonable doubt that
+two great pre-Cambrian systems of rock exist in the north-west of
+Scotland.
+
+These two systems differ so entirely from each other that their
+respective areas can be defined with minute accuracy. The uppermost
+consists chiefly of dull reddish sandstones with conglomerates, and
+especially towards their base in Rosshire, some bands of dark grey
+shale, the whole having a thickness of at least 8,000 or 10,000 feet,
+though as both the base and the top of the series are marked by strong
+unconformabilities, the whole original thickness of deposits is nowhere
+seen. As these rocks are well developed around Loch Torridon, they
+were named by Nicol the Torridon Sandstone--a designation which has
+more recently been shortened into "Torridonian." The lower system is
+mainly composed of various foliated rocks which may be embraced under
+the general term "gneiss." These masses present the usual characters of
+the so-called "fundamental complex", "Urgebirge," or "Archæan Series"
+of other countries. The contrast between the thoroughly crystalline,
+gnarled, ancient-looking gneisses below, and the overlying, nearly
+horizontal Torridonian conglomerates, sandstones, and shales, which
+are largely made out of their debris, is so striking that every
+observer feels persuaded that in any logical system of classification
+they can not be both placed in the same division of the geological
+record. They are certainly both pre-Cambrian, but they must belong
+to widely separated eras, and must have been produced by entirely
+different processes. If it is proposed to regard the gneisses as
+"Archæan," we must refuse to include the Torridonian strata in the
+same section of pre-Cambrian time. But so much uncertainty exists as
+to the application of this term Archæan, examples are so multiplying
+wherein what was supposed to be the oldest and truly Archæan rock is
+found to be intrusive in rocks that were taken to be of much younger
+date, and there are such slender grounds for correlating the so-called
+Archæan rocks of one country with those of another, that I prefer for
+the present, at least, not to use the term at all. Let me very briefly
+state some of the main characteristics of the two sharply contrasted
+rock-systems of the north-west of Scotland.
+
+The oldest gneiss of that region was originally called "Lewisian" by
+Murchison, from its large development in the Island of Lewis, and I
+think it would be, for the present at least, an advantage to retain
+this geographical appellation. At first this "fundamental gneiss"
+was thought to be a comparatively simple formation, and the general
+impression probably was that it should be regarded as a metamorphic
+mass, produced mainly from the alterations of very ancient stratified
+rocks. Its foliation-planes were believed to be those of original
+deposit which by terrestrial disturbance had been thrown into numerous
+plications and corrugated puckerings. But a detailed study of this
+primeval rock has revealed in it a far more complicated structure. The
+supposed bedding-planes have been ascertained to have nothing to do
+with sedimentary stratification, and the gneiss has been resolved into
+a complex series of eruptive rocks, varying from a highly basic to an
+acid type, and manifestly belonging to different times of extrusion.
+With the exception of one district, to which I shall immediately refer,
+no part of the whole region yet examined has revealed to the rigid
+scrutiny of my colleagues of the Geological Survey, any trace of rocks
+which can be regarded as probably of other than igneous origin. It is
+true that our researches have been hitherto confined to the mainland
+of Scotland, the large area of the Outer Hebrides, which consists of
+similar gneisses, remaining to be explored. It is therefore possible
+that indisputable evidence of an ancient sedimentary series through
+which the gneiss was originally protruded, may yet be discovered in
+the unexplored islands. But taking the gneiss as at present known in
+Sutherland and Rosshire, we find it to be generally coarse in texture,
+rudely foliated, and passing sometimes into massive types in which
+foliation is either faintly developed or entirely absent. Much of this
+gneiss is considerably more basic than the more typical rocks to which
+the term gneiss was formerly restricted. It consists of plagioclase
+felspar with pyroxene, hornblende, and magnetite, sometimes with blue
+opalescent quartz, and sometimes with black mica. These predominant
+minerals are segregated in different proportions in the different
+bands, some bands consisting mainly of pyroxene or hornblende, with
+little or no plagioclase, others chiefly of plagioclase, with small
+quantities of the ferro-magnesian minerals and quartz, others of
+plagioclase and quartz, others of magnetite. This separation of mineral
+constituents can hardly be attributed to mere mechanical deformation.
+It rather resembles the segregation layers which may be studied in
+intrusive sills and other deep-seated masses of eruptive material, and
+which are obviously due to a process of separation that went on while
+the igneous magma was still in a liquid or viscous condition. At the
+same time it is manifest that extensive dynamical changes have affected
+the rocks since the appearance of this original banded structure.
+
+There is further evidence that beside the original eruptive masses,
+which for want of any means of discriminating their relative dates
+of protrusion must in the meantime be regarded as belonging to
+one eruptive period, other portions of igneous material have been
+subsequently and at successive epochs, after the first mechanical
+deformations, injected into the body of the original gneiss. These
+consist of dykes of basalt and dolerite, followed by still more basic
+peridotites and picrites, and lastly by emanations from a distinctly
+acid magma in the form of granites. The oldest or doleritic dykes form
+a wonderful feature in the gneiss, from their abundance, persistence
+and uniformity of trend in a west-northwest direction. They have no
+parallel in British Geology until we reach the crowded dykes of older
+Tertiary time.
+
+Throughout this remarkable complex of eruptive material, though its
+different portions present many features that may be compared with
+those of intrusive bosses and sheets belonging to later geological
+periods, there is no trace of any superficial volcanic manifestation.
+No tuffs or agglomerates or slaggy lavas have been detected, such
+as might serve to indicate the ejection of volcanic materials to
+the surface. All the phenomena of the Lewisian gneiss point to the
+consolidation of successively protruded portions of eruptive material
+at some depth within the crust.
+
+Nevertheless it may yet be possible to show that these deep seated
+masses have been injected into rocks of older date and of sedimentary
+origin, and that they have communicated with the surface in true
+volcanic eruptions. I have already alluded to one limited area where
+various rocks exist, distinctly different from the prevalent types in
+the Lewisian gneiss. In the area which is traversed by the long valley
+of Loch Maree in western Rosshire, there occur clay-slates, fine mica
+schists, graphitic schists, and saccharoid limestones. These rocks
+remind us of some of the prevalent members of a series of metamorphosed
+sediments. The minerals enclosed in the marbles are just such as might
+be expected in the metamorphic aureole of a granite boss, piercing
+limestone. But the relations of this group of rocks to the ordinary
+gneiss of the region are not quite so clear as could be desired, though
+they seem to point to these rocks being surrounded by and enclosed
+within the gneiss.
+
+The detailed field-work of the officers of the Geological Survey has
+made known the remarkable amount of mechanical deformation which the
+various rock-masses composing the Lewisian gneiss have undergone.
+These rocks have been compressed, crushed, and drawn out, until what
+were originally massive crystalline protrusions have been converted
+into perfect schists. The dykes of dolerite have been transformed
+into hornblende-schists and the granitic pegmatites have been reduced
+to a kind of powder which has been rolled out so as to simulate the
+flow-structure of a lava. There is evidence that most, if not all, of
+this dynamical change was effected long before the deposition of the
+Torridonian series, for the latter rests in nearly horizontal sheets,
+with a strong unconformability upon the crushed and sheared gneiss.
+
+_Torridon Sandstone._ This group of rocks covers only a limited area
+in the north-west of Scotland, but it must once have spread over a
+far more extensive region. It reaches a thickness, as I have said, of
+8,000 or 10,000 feet, and consists almost wholly of dull, purplish-red
+sandstones, often pebbly, and bands of conglomerate. Dark grey shales,
+already alluded to as occurring towards the base of the series, are
+repeated also in the highest visible portion, and have yielded tracks
+of what seem to have been annelids and casts of nail-like bodies which
+may have been organic. I have said that the Torridonian deposits
+which were classed by Murchison as Cambrian, have been proved by the
+discovery of the _Olenellus_ zone in an unconformable position above
+them, to be of pre-Cambrian age. Except along the line of disturbance
+to which I shall immediately refer, these strata are quite unaltered.
+Indeed, in general aspect they look as young as the old red sandstones
+with which Hugh Miller identified them. It is at first hard to believe
+that such flat undisturbed sandstones are of higher antiquity than
+the very oldest Palæozoic strata which are so generally plicated and
+cleaved.
+
+The interval of time between the deposition of the Torridon Sandstone
+and of the overlying Cambrian formations must have been of enormous
+duration, for the unconformability is so violent that the lowest
+Cambrian strata, not only transgressively overspread all the
+Torridonian horizons, but even lie here and there directly on the
+old gneiss, the whole of the intervening thick mass of sandstone
+having been there removed by previous denudation. At Durness, in the
+north of Sutherland, about 2000 feet of Cambrian (possibly in part
+Lower Silurian) strata can be traced, the lower portion consisting
+of quartzites, the central and upper parts of various limestones,
+sometimes abundantly fossiliferous. Nowhere else in the north of
+Scotland can so thick a mass of early Palæozoic rocks be seen.
+Elsewhere the limestones have been in large measure replaced by a
+complex group of schistose rocks which rest upon the Cambrian strata,
+and like them dip, generally at gentle angles, towards the east. It
+was the opinion of Murchison, and was commonly admitted by geologists,
+that these overlying schists represented a thick group of sediments,
+which, originally deposited continuously after the limestones, had
+been subsequently altered into their present condition by regional
+metamorphism. They were variously named the "Eastern schists," the
+"younger gneiss," the "gneissose and quartzose flagstones." Nicol,
+who at first shared the general opinion regarding them, afterwards
+maintained that they did not belong to a later formation than the
+limestones, but were really only the old gneiss, brought up again from
+beneath by enormous dislocations and over-thrusts. We now know from the
+labors of Professor Lapworth and the officers of the Geological Survey,
+that Murchison and Nicol had each seized on an essential part of the
+problem, but that both of them had missed the true solution. Murchison
+was in error in regarding his younger gneiss as a continuous sequence
+of altered sedimentary rocks conformably resting on the Cambrian (or
+to use his terminology, Lower-Silurian) formations. But he sagaciously
+observed the coincidence of dip and strike between the schists and
+sedimentary rocks below them and inferred that this coincidence,
+traceable for many leagues, proved that the metamorphism which had
+given these schists their structure must have taken place after the
+deposition of the Durness limestones. Nicol, on the other hand, with
+great insight recognized that there was no continuous sequence above
+those limestones, but that masses of the old gneiss had been thrust
+over them by gigantic faults. But he failed to see that no mere faults
+would account for the coincidence between the structural lines just
+referred to in the Cambrian strata, and in the overlying schists, and
+that the general tectonic structures and lithological characters of the
+eastern schists differed in many respects from those of the Lewisian
+gneiss.
+
+The problems in tectonic geology presented by the complicated
+structures of the northwest of Scotland have been ably worked out
+by the officers of the Geological Survey, to whose report in the
+_Quarterly Journal of the Geological Society_ for 1888, I would
+refer for full details. It has been shown that, besides stupendous
+dislocations and horizontal displacements, the rocks have been cut into
+innumerable slices which have been driven over each other from the
+eastward, while at the same time there has been such a general shearing
+of the whole region that for many hundreds of square miles the original
+rock-structures have been entirely effaced, and have been replaced
+by new divisional planes, which, when they approach the underlying
+Cambrian strata, are roughly parallel with the bedding planes of these
+strata.
+
+In this region, therefore, we have striking proofs of a stupendous
+post-Cambrian regional metamorphism. But there is still much
+uncertainty regarding the geological age of the rocks which have been
+affected by it. There can be no doubt that large masses of the old
+gneiss, torn up from below, have been thrust bodily westward for many
+miles, and are now seen with their dykes and pegmatites resting on the
+Durness limestones and quartzites. It is equally certain that in other
+districts huge slices of the Torridon sandstones have been similarly
+treated. But where all trace of original structure has disappeared, we
+have, as yet, no means of definitely determining from what formation
+the present eastern schists have been produced. The ordinary gneissose
+and quartzose flagstones do not appear to me to be such rocks as could
+ever be manufactured by any chemical or mechanical process out of the
+average type of Lewisian gneiss. I have long held the belief that
+they were originally sediments, but whether they represent altered
+Torridon Sandstone, or some clastic formations which may have followed
+the Durness limestones, but which have been everywhere and entirely
+metamorphosed, remains for future discovery. For my present purpose,
+it is sufficient to observe that, in the meantime, as we can not be
+sure of the origin of most of the rocks, which, between the West Coast
+and the line of the Great Glen, have been subjected to a gigantic
+post-Cambrian regional metamorphism, it seems safest to exclude them
+from an enumeration of the pre-Cambrian rocks of Britain.
+
+_Dalradian._ East of the line of Great Glen, which cuts the Scottish
+Highlands in two, another group of crystalline schistose rocks is
+largely developed. It consists mainly of what were undoubtedly
+originally sedimentary deposits, though they are now found in the form
+of quartzites, phyllites, graphitic schists, mica-schists, marbles,
+and various other foliated masses. With them are associated numerous
+eruptive rocks, both acid and basic, sometimes still massive and
+easily recognizable as intrusive, sometimes more or less distinctly
+foliated and passing into different gneisses, hornblende-schists,
+chloritic-schists, etc. Though it is not always possible in such a
+series of metamorphic rocks to be certain of any real chronological
+order of succession, those of the Highland tracts have now been mapped
+in detail over so wide an area, that we are probably justified in
+believing that a definite sequence can be established among them.
+These masses must be many thousand feet thick. Their succession and
+association of materials are so unlike those of any of the known older
+Palæozoic rocks of Britain, that they can hardly be the metamorphosed
+equivalents of any strata which can be recognized in an unaltered
+condition in these islands. Some traces of annelid casts have been
+found in the quartzites, but otherwise the whole series has remained
+entirely barren of organic remains.
+
+What then is the age of this important series? I must confess that in
+the meantime I can give no satisfactory answer to this question. I
+have proposed, for the sake of distinction and convenient reference,
+to call these rocks "Dalradian." Murchison supposed them to be a
+continuation of his Durness quartzites, limestones, and "younger
+gneiss." His belief may still prove to be in some measure well founded.
+But at present we have no means of deciding whether the quartzites and
+limestones of the Central Highlands are the more altered equivalents of
+the undoubtedly Cambrian strata of the north-west. It is possible that
+in the vast mass of metamorphosed rocks constituting the wide stretch
+of country from the northern headlands of Aberdeen to the south-western
+promontories of Argyllshire, there may be portions of the old Lewisian
+gneiss, tracts of highly altered Torridon sandstone, belts of true
+counterparts of the Cambrian quartzites and limestones of Durness,
+and, what should not be forgotten, considerable portions of some later
+sedimentary series which may have followed these limestones, but
+which, by the great dislocations already referred to, have disappeared
+from the north-west of Scotland. We are gradually learning more of
+these rocks, as the detailed mapping of them by the Geological Survey
+advances, and when the ground on either side of the Great Glen is
+surveyed, it may be possible to speak with more certainty regarding
+their true geological relations.
+
+A glance at a geological map of the British Isles will show that the
+metamorphic rocks of the south-western Highlands of Scotland are
+prolonged into the north of Ireland, where they spread over a region
+many hundred square miles in extent. They retain there the same general
+character and present the same difficult problems as to their true
+stratigraphical relations. Quite recently, however, a new light seems
+to have arisen upon these Irish rocks. My colleagues on the Irish
+Branch of the Geological Survey have detected several detached areas
+of coarse gneisses, which in many respects resemble parts of the
+Lewisian gneiss of north-west Scotland. In some cases these areas lie
+amidst or close to "Dalradian" rocks, but with that obstinacy, which
+so tries the patience of the field-geologist, they have persistently
+refused to disclose their true original position with regard to these.
+Some fault, thrust-plane, tract of boulder-clay or stretch of bog
+is sure to intervene along the very junction-line where the desired
+sections might have been looked for. There can be little doubt that
+a strong unconformability exists between them. A close examination of
+the ridge of old gneiss in Tyrone and Fermanagh showed me that though
+the actual basement-beds of this Dalradian series could not be seen
+resting on the coarse gneiss, the lithological character, and tectonic
+arrangement of this series are only explicable on the supposition of a
+complete discordance between it and the gneiss. As these two groups of
+rock have never been found in close proximity in Scotland, and as the
+determination of the true age of the Dalradian series is a question of
+such great stratigraphical importance in the general mapping of the
+United Kingdom, I requested Mr. A. McHenry, of the Geological Survey of
+Ireland, to continue the tracing of the mutual boundaries of the old
+gneiss of the Ox Mountains and the Dalradian series in County Mayo.
+He informs me that he has found in that series a conglomerate full
+of blocks of the old gneiss, and resting in one locality apparently
+unconformably upon it. If this observation is confirmed it will finally
+set at rest the relative position of the coarse massive gneiss and
+some portion, at least, of the Dalradian series. Of course there is
+no absolute proof that the coarse gneisses of Ireland are really the
+equivalents of the Lewisian masses which they so closely resemble. But
+there is a strong presumption in favor of their identity.
+
+In England and Wales many detached areas of rock have been claimed as
+pre-Cambrian, and successive formations have been classified among
+them. I have already dealt in part with this question, and without
+attempting here to review the voluminous literature of the subject, I
+will content myself with stating briefly what seems to me to have been
+established on good evidence.
+
+There can not, I think, be now any doubt that small tracts of gneiss,
+quite comparable in lithological character to portions of the Lewisian
+rocks of the north-west of Scotland, rise to the surface in a few
+places in England and Wales. In the heart of Anglesey, for example,
+a tract of such rocks presents some striking external or scenic
+resemblance to the characteristic types of ground where the oldest
+gneiss forms the surface in Scotland and the west of Ireland. In the
+Malvern Hills another small knob of somewhat similar material is
+obviously far more ancient than the Cambrian rocks of that locality.
+There may possibly be still some further exposures of similar rocks in
+the south of England, as for instance in southern Cornwall. In Anglesey
+a series of schists, quartzites and limestones has been included by
+Mr. J. F. Blake with the coarse gneiss above referred to, and a thick
+higher group of slates in what he terms the "Monian" system. These
+schists, quartzites and limestones present a close resemblance to the
+Dalradian series of Scotland and Ireland, and the quartzites, like
+those of the Highlands, contain worm-burrows. The coarse gneiss, as
+I have said, may be compared in general character with parts of the
+Lewisian rocks, so that we seem to have here, as in Ireland, two groups
+of schistose rocks, and both of these must be much older than the
+unaltered Cambrian strata which lie above them.
+
+Along the eastern borders of Wales, there is an interrupted ridge of
+igneous rocks which were originally supposed to have broken through the
+older Palæozoic formations, but which now, owing mainly to the labors
+of Dr. Callaway and Professor Lapworth, are shown to be older than
+the base of the Cambrian system. These rocks consist of spherulitic
+and perlitic felsites, with volcanic breccias and tuffs. They are
+undoubtedly older than the _Olenellus_ zone. Though the evidence is
+not quite satisfactory, they may not impossibly lie at the base of
+a vast mass of sedimentary rocks forming the ridge of the Longmynd.
+In that case the whole of the Longmynd succession with the volcanic
+group at its base must be pre-Cambrian and lie unconformably below the
+_Olenellus_ zone. Dr. Callaway has proposed the name "_Uriconian_"
+for this volcanic group, while the sedimentary series has been termed
+"_Longmyndian_." On the supposition that the unconformability is
+established, there would here be a vast mass of stratified and partly
+erupted material forming a pre-Cambrian formation. Whether in that case
+any portion of this English series is the equivalent of the Torridonian
+rocks of Scotland remains to be determined. The northwestern part of
+the Longmynd ridge is made of red sandstones and conglomerates, which
+certainly resemble the Torridonian rocks of Ross and Sutherland.
+
+At the base of the Cambrian rocks in Wales, Dr. Hicks has described a
+marked volcanic series under the name of "Pebidian," which he claims as
+pre-Cambrian, alleging that it is separated from the Cambrian system
+by an unconformability, and a band of conglomerates. I have carefully
+studied the evidence on this ground, and have come to the conclusion
+that there is no unconformability at the line in question, but that the
+ordinary Cambrian strata graduate downwards into the volcanic group
+and can not be disjoined from it. I therefore regard the so-called
+"Pebidian" as merely marking the duration of a volcanic period in early
+Cambrian time.
+
+It will thus be seen that according to my view the unmistakably
+pre-Cambrian rocks of Britain consist of, first and oldest, the
+Lewisian gneiss; second, the Torridonian sandstones and conglomerates.
+The Uriconian and Longmyndian formations may prove to be in part or
+in whole equivalents of the Torridonian. The Dalradian rocks have not
+yet had their position determined. They may possibly mark a distinct
+pre-Cambrian series, but it seems quite as probable that they are only
+a metamorphic complex in which Archæan, Torridonian and Cambrian, or
+even Lower Silurian rocks are included.
+
+                                           =Sir Archibald Geikie=,
+  Director-General of the Geological Survey of Great Britain and Ireland.
+
+
+
+
+ARE THERE TRACES OF GLACIAL MAN IN THE TRENTON GRAVELS?
+
+
+In a paper published in _Science_, Nov. 25. 1892, I undertook to study
+the evidence relating to paleolithic man in the eastern United States
+from a new point of view,--that furnished by certain recently acquired
+knowledge of the contents of quarries and shops where modern aboriginal
+flaked implements were made. It was shown that all rudely flaked forms
+could be sufficiently accounted for without the necessity of assuming
+a very rude state of culture, and that any people, paleolithic or
+neolithic, would in roughing out blades--the principal product of the
+flaking process--produce precisely these forms and in great numbers
+as refuse. It further appeared that the finding of these objects in
+sporadic cases in glacial gravels or in any formation whatsoever, could
+not be considered as proving or tending to establish the existence of
+a particular grade of stone-age culture for the region in which the
+formation occurs, since they may as readily pertain to a neolithic
+as to a paleolithic status. It was conclusively shown that no worked
+stone that can with reasonable safety be called an implement has been
+reported from the gravels, and that it is therefore clearly useless,
+not to say unscientific, to go on enlarging upon the evidence of an
+American paleolithic period and multiplying theoretic details of its
+culture.
+
+I now propose to review briefly the question of the age of our
+so-called paleolithic implements, the questions of the _grade_ of
+a given feature of culture and of the _age_ or chronologic place
+of that culture being very properly treated separately, as they
+depend for their support upon distinct classes of evidence. During
+the past summer, 1892, certain important items of new evidence have
+been discovered bearing upon the question of the occurrence or
+non-occurrence of rudely flaked stones or of any artificial objects
+whatsoever in the normal gravels of the Delaware Valley, and it
+therefore becomes necessary to examine somewhat critically such of the
+published evidence as seems to be seriously affected by these recent
+observations.
+
+It may be stated in beginning that no one disputes the glacial age of
+the Trenton gravels. The question to be discussed is simply this,--is
+the evidence satisfactory that works of art have been found in these
+gravels? Nothing else need be asked or answered. I do not take up
+this subject because I love controversy; disputation is really most
+distasteful to me. It happens that under the Bureau of Ethnology of the
+Smithsonian Institution I have been assigned to the work of making a
+survey of the archeology of the Atlantic coast region in which large
+areas, especially in states south of Mason and Dixon's line, remained
+almost untouched by investigators, and two years have been consumed
+mainly in these southern areas. But there are questions that refuse
+to be confined to definite geographic limits, and evidence secured in
+one section is sometimes found to bear so directly and forcibly upon
+problems pertaining primarily to other sections that the student of
+these problems must perforce become a free lance, and unhesitatingly
+enter any province promising results of value, howsoever fully occupied
+it may be by other investigators. One of the most interesting and
+important questions growing out of the study of American archeology
+has, as we have seen, arisen in the Delaware Valley, and the turn taken
+by some of my work in the south and west is such that I cannot pass
+this question by without consideration. The necessity of taking up
+the subject of glacial man became more and more apparent as the years
+passed on, and people continued to say to me, "You must go to Trenton;
+we are not satisfied with the present status of the question there; the
+evidence arrayed in favor of the theory of a paleolithic gravel man
+needs critical examination."
+
+The difficulty of taking up and re-examining evidence, of which the
+record only remains, is, however, very great, since in most cases
+the evidence rests upon or consists of field observations, and these
+cannot be recalled or repeated, and there is absolutely no means of
+testing directly the value of what is recorded. One may seek either to
+verify or to discredit the promulgated theories, but years of search
+may fail to produce a single new item of evidence bearing decisively
+upon the subject. It is possible that at one period numerous finds of
+implements should be reported from certain portions of the gravels,
+and that afterwards the whole remaining body of these formations
+should be worked over and searched without securing a trace of art;
+yet this latter evidence, being negative, need not necessarily be
+considered sufficient to overturn the original positive evidence if
+that happens to be of a high class. There is not the least doubt,
+however, that positive evidence may be so impaired by various defects
+and inconsistencies, that, unsupported by renewed and well verified
+observations, it will finally yield to the negative forces; and if
+the theories of a gravel man in the eastern United States, howsoever
+fortified by accumulated observations, are not really properly
+supported in every way, they are bound in time to fall to the ground.
+All I can reasonably hope to do now is to have the evidence relating to
+glacial man placed on trial, and so fully examined and cross-examined
+that those who accept gravel man need not longer do so blindly without
+knowing that there are two sides to the question, and those who do not
+accept him may know something of the reasons for the belief that is in
+them.
+
+The evidence employed to prove the presence of a race of men in
+the Delaware Valley in glacial times is confined almost wholly to
+the alleged discovery of rude implements in the glacial gravels.
+Practically all the evidence has been collected by Dr. C. C. Abbott,
+and upon his skill as an observer, his faithfulness as a recorder,
+his correctness of judgment and his integrity of character, the whole
+matter stands. Many visitors, men of high repute in archeology and
+geology, have visited the site, but the observations made on such
+occasions appear not to have been of a nature to be of great value in
+evidence, the finds being doubtful works of art or not having properly
+established relationships with the gravels in place. In the discussion
+of gravel man in eastern America a wide range of objects and phenomena
+has been considered, but the real evidence, upon which the theory of
+an ancient race and a peculiar culture must depend, is furnished by a
+hundred pieces--more or less--of rudely flaked stones said to have come
+from the gravels in place. And now what can be said with reference to
+this series of flaked stones further than that they are reported by the
+collector to have been found in the gravels at definite stated depths?
+I have elsewhere shown that they are not demonstrably implements
+in any case, that they are identical in every respect with the
+quarry-shop rejects of the American Indian, that they do not closely
+resemble any one of the well established types of European paleolithic
+implements, and that they are not a sufficient index of a particular
+stage of culture. I shall now present such reasons as there may be
+for the belief, held by many, that they were not really found in the
+undisturbed glacial gravels.
+
+It is generally understood that the earliest reported gravel finds of
+importance were made on the banks of Assanpink creek within the city
+limits of Trenton, where the gravels to a thickness of twenty feet or
+more were exposed in a railway cutting. Later the river bluff near the
+lower end of the city, where the gravels were exposed to a depth of
+from twenty-five to forty feet, yielded large numbers. These two sites,
+so far as I can learn, furnished at least three-fourths of the finds in
+place. Other specimens were found singly in slight natural exposures,
+and in excavations for cellars, sewers, etc., at various points within
+the city limits.
+
+The river bluff was for a considerable period the favorite hunting
+ground of the searchers for rudely flaked stones, and many specimens
+were collected. The gravels were exposed in a steep, nearly straight
+bank, several hundred yards in length, the base of which was washed by
+the river. There can be no question that Dr. Abbott and others have
+found shaped objects of various classes upon and in the face of this
+river bluff, and the visitor to-day, although the bluff is now buried
+almost completely under city refuse, will hardly fail to find some
+rudely flaked form in the deeper gullies or upon the narrow river bank
+or beach at the base. Dr. Abbott explicitly states[1] that he obtained
+certain of these specimens from the gravel outcrops, and that they were
+not in talus formations, but in undisturbed deposits. How then is it
+possible to do otherwise than accept these statements as satisfactory
+and final?
+
+[1] Abbott, C. C. Primitive Industry, pp. 493-510.
+
+[Illustration: =Fig. 1.= Sketch map of the Trenton bluff, showing the
+relation of the sewer trench to the "implement" yielding slope.... a-b
+section line, =Fig. 2=.]
+
+Very recently, however, fortunate circumstances have brought the
+evidence furnished by this site again within our reach, thus enabling
+us to re-open the discussion under favorable conditions. What I had
+for some time desired to do in this case was, what I had already done
+at Piny Branch, D. C., and at Little Falls, Minn., to open a trench
+into the face of the bluff, and thus secure evidence for or against
+the theory of a gravel man. This measure was, however, rendered
+impracticable by the occupation of the bluff margin by a city street;
+but it happened last summer that the city authorities, desiring to
+improve the sanitary condition of the city, decided to open a great
+sewer through this very bluff to get a lower outlet to the river. A
+trench twelve feet wide and some thirty feet deep, the full depth
+of the exposed gravels, was carried along the bluff just inside of
+its margin, opening out into the river at the point where the bluff
+turns toward the north-east. It was a trenching more complete and more
+satisfactory than any of which I had ever dreamed. At no point for the
+entire length of the bluff did the excavation depart more than forty
+feet from the line of the terrace face--from the upper margin of the
+slope upon which such plentiful evidence of a supposed gravel man had
+been obtained. The accompanying map and section, Figs. 1 and 2, will
+indicate the location of the trench, and show the exact relations of
+the natural and artificial exposures of the gravels.
+
+[Illustration: =Fig. 2.= Sections made by the river and by the sewer,
+the former yielding many "implements," the latter yielding none.]
+
+I made several visits to the place, descended frequently into the great
+cut and examined the gravels and their contents with the utmost care,
+but without securing a trace of art. Recognizing the vital importance
+of utilizing to the fullest extent this opportunity of testing the
+art-bearing nature of the gravels at this point, I resolved to
+undertake a systematic study of the subject. Summoning my assistant,
+Mr. William Dinwiddie, from his field of operations in the South, I had
+him spend upwards of a month at the great trench, faithfully watching
+the gravels as they were exposed. Mr. Dinwiddie had worked three years
+under my personal direction, and had helped open upwards of twenty
+trenches through similar gravel deposits, and was therefore well
+qualified for the work. Prof. W. J. McGee, Prof. R. D. Salisbury, Dr.
+Stewart Culin and Dr. Abbott also visited the place one or more times
+each. Relics of art were found upon the surface and in such portions of
+the talus as happened to be exposed, but nothing whatever was found in
+the gravels in place, and the search was closed when it became fully
+apparent that the case was hopeless.
+
+It may be claimed that the conditions under which gravels are exposed
+in trenching as it progresses, are not as favorable for the collection
+of enclosed relics as where exposed by natural processes of weathering.
+This is true in a certain measure, as specimens may be obscured by
+the damp clinging sand which forms the matrix of the gravels. This,
+however, would interfere but little with the discovery of large flaked
+stones, such as we were led to expect in this place, and this slight
+disadvantage in detecting shaped pieces in fresh exposures is more
+than over-balanced by the treachery of weathered surfaces which often
+give to intrusive objects the appearance of original inclusion. The
+opportunity for studying the gravels in all their phases of bedding,
+composition and contents, was really excellent, and no one could watch
+the constantly renewed exposures hour after hour for a month without
+forming a most decided notion as to the implement bearing qualities
+of the formation. Not the trace of a flaked stone, or of a flake or
+artificial fragment of any kind was found, and we closed the work
+with the firm conviction that the gravels exposed by this trench were
+absolutely barren of art. But Dr. Abbott claims to have found numerous
+implements in the bluff face a few feet away and in the same gravels.
+If this is true, the conditions of glacial occupation of this site
+must have been indeed remarkable. It is implied that during the whole
+period occupied by the melting of the ice sheet within the drainage of
+the Delaware valley the hypothetical rude race lived on a particular
+line or zone afterwards exposed by the river to the depth of 30 feet,
+leaving his strange "tools" there by the hundreds, while another line
+or zone, not more than forty feet away at most, exposed to the same
+depth by an artificial trench, was so avoided by him that it does not
+furnish the least memento of his presence. One vertical slice of the
+gravels twelve feet thick does not yield even a broken stone, while
+another slice not probably one-half as thick, cut obliquely through
+the gravels near by, has furnished subject-matter for numerous books
+and substantiation for a brace of theories. That no natural line of
+demarcation between the two section lines is possible, is shown by
+the fact that the formations are continuous, and that the deposits
+indicate a constant shifting of lines and areas of accumulation;
+thus it was impossible for any race to dwell continuously upon any
+spot, line or plane. This is well shown in the section, Fig. 3, which
+gives the relations of the art-producing section of Dr. Abbott to the
+non-art-producing section of the sewer. The gravels were laid down
+entirely irrespective of subsequent cutting, natural or artificial;
+yet we are expected to believe that a so-called gravel man could have
+resorted for a thousand years to the space _a_, leaving his half
+shaped or incipient tools at all stages of the gravel building from
+base to top, failing entirely to visit a neighboring space _b_, or to
+leave there a single flake to reward the most faithful search. It is
+much easier to believe that one man should err than that a guileless
+race should thus conspire with a heartless nature to accomplish such
+extraordinary results. The easier explanation of the whole matter is
+that the objects found by Dr. Abbott were not really in the gravels,
+but that they are Indian shop-refuse settled into the old talus
+deposits of the bluff, and that his eager eyes, blinded by a prevailing
+belief in a paleolithic man for all the world alike, failed to observe
+with their wonted keenness and power.
+
+[Illustration: =Fig. 3.= _a_, Reputed "implement" producing zone of the
+river front. _b_, Barren zone of sewer.]
+
+But this case does not stand alone. The first discoveries of supposed
+gravel implements are said to have been made when the Pennsylvania
+Railway opened a road bed through the creek terrace on the site of the
+present station. At first numerous specimens of rudely flaked stones
+were reported, and the locality became widely known to archeologists,
+but the implement bearing portions of the gravels--and this is a most
+significant fact--were limited in extent, and the deposit was soon
+completely removed, the horizontal extension containing nothing. At
+present there are excellent exposures of the full thickness of the
+gravels at this point, but the most diligent search is vain, the only
+result of days of examination being a deep conviction that these
+gravels are and always were wholly barren of art.
+
+It thus appears that here as well as upon the river front, the works
+of art were confined to local deposits, limited horizontally but not
+vertically, and a strong presumption is created that the finds were
+confined to redistributed gravels settled upon the terrace face in the
+form of talus. Dr. Abbott states that "at that point where I gathered
+the majority of specimens there is a want of stratification."[2] It
+is well known that such rearranged deposits are often difficult to
+distinguish from the original gravels. In trenching an implement
+producing terrace at Washington--where the conditions were probably
+quite similar to those at the Trenton railroad station--I passed
+through eighty feet of redistributed talus gravels before encountering
+the gravels in place, and so deceptively were portions of these
+deposits re-set that experts in gravel phenomena were unable to decide
+whether they were or were not portions of the original formation
+(cretaceous). The question was finally settled by the discovery of
+artificially shaped stones in and beneath the deposits.
+
+[2] Abbott, C. C. 10th Annual Report of the Peabody Museum, p. 41.
+
+Again, an implement bearing deposit of gravel was recently discovered
+by the late Miss F. E. Babbitt at Little Falls, Minnesota, and
+sufficient (a very little) digging was done to satisfy the discoverer,
+and all paleolithic archeologists as well, that the objects were really
+imbedded in the glacial gravels. In the summer of 1892 I visited the
+place and carried a trench twenty feet horizontally into the terrace
+face on the "implement bed" level before encountering the gravels in
+place. The talus deposits were several feet thick, and were of such
+a nature that their true character could not be determined without
+careful and extensive trenching. The whole talus deposit was here
+well stocked with Indian quartz quarry-shop rejects, which were as
+usual of paleolithic types, and it was but natural that Miss Babbitt's
+conclusions, although based as they necessarily were upon inexpert
+observations, backed by such well known "types" of "implements" should
+be unhesitatingly accepted by believers.
+
+The occurrence of these telling examples of the deceptive appearance
+of re-set gravels would seem to justify and emphasize the conviction
+created by a critical examination of the two leading so-called
+paleolithic sites at Trenton, that Dr. Abbott, notwithstanding his
+asseverations to the contrary, has been deceived. Very strong support,
+it seems to me, is given to this conclusion by the recently published
+opinion of the late Dr. H. Carvill Lewis, a glacialist familiar
+with the Trenton region, and with the work of Dr. Abbott at the
+period of his paleolithic castle building. Dr. Lewis is reported to
+have maintained before an open meeting of the Academy of Science in
+Philadelphia "that what Dr. Abbott believed to be undisturbed layers
+(of gravel) were those of an ancient talus."[3] This remark may refer
+to both the main sites--the one at the railroad station and the other
+at the river front--or possibly only to the former. I have also heard
+it stated that that eminent scholar, Dr. Leidy, who must have had ample
+opportunities of forming correct opinions upon the subject, held pretty
+much the same views of Dr. Abbott's finds.
+
+[3] Brinton, D. G., Science, Oct. 28, p. 249.
+
+[Illustration: =Fig. 4.= A freshly formed gravel bluff.]
+
+[Illustration: =Fig. 5.= Early stage of talus formation.]
+
+[Illustration: =Fig. 6.= An ancient talus.]
+
+To make the above criticism entirely clear, a few words of explanation
+of talus phenomena may be added. As a river cuts its channel deeper
+and deeper into deposits of gravel a section is gradually exposed, but
+the gravels break down readily under atmospheric influences and the
+exposed face does not retain a high angle. The upper part crumbles and
+descends toward the base, there to rest against the slope or to be
+carried away by the stream. A supposititious case will be convenient
+for illustration. A gravel terrace twenty feet in height is encroached
+upon by the river at high water and undermined, and the face breaks
+down vertically, leaving an exposure as illustrated in Fig. 4. In a
+very short time the upper portions become loosened and fall below,
+giving a steep slope as seen in Fig. 5. The process goes on with
+gradually decreasing rapidity, and if the river does not again encroach
+seriously, a practically stable slope is reached, as shown in Fig.
+6. Such a talus may be hundreds or even thousands of years old, but
+there is rarely any means of determining its exact age. If the gravels
+are homogeneous in character, the talus will simulate their normal
+condition so completely that the distinction cannot be made out in
+ordinary gullies or by unsystematic digging. If the gravels contain
+varied strata the talus will be composite, and will be more readily
+distinguished from at least portions of the material in place.
+
+Now it is important to observe what may be the possible art contents
+of such a talus as that shown in Fig. 6. It may contain all objects
+of art originally included in that portion of the gravels represented
+by _a_, _b_, _c_, together with all articles that happened to be upon
+the surface _b_, _c_, beside such objects as may have accumulated from
+dwelling or shop work upon its own surface, after the slope became
+sufficiently reduced to be occupied for these purposes. A talus is
+therefore liable to contain, and in the utmost confusion, relics of all
+periods of occupation, supposing always that there were such periods,
+from the beginning of the formation of the gravel deposits down to the
+present moment. As a rule such a talus, if art-containing, will have a
+large percentage of shop and quarry-shop refuse, for the reason that
+the exposed gravels, and the banks and beds of rivers cutting them,
+furnish, as a rule, a good deal of the raw material utilized by workers
+in stone, and the shops in which the work was done are usually located
+upon the slopes and outer margins of the terraces. Although there is
+the possibility of very considerable age for these talus deposits,
+it is unlikely that any of them date back as far as the close of the
+glacial epoch or at all near it, for rivers change back and forth
+constantly, undermining first one bank and then the other, so that a
+very large percentage of our talus deposits have been formed well
+within the historic period.
+
+At Trenton the constantly exposed gravel banks afforded considerable
+argillite in bowlders, fragments and heavy masses, as well as some
+other flakable stones of inferior quality little used, and it is
+inevitable that the Indian who dwelt upon the shores of the river
+should have sought the workable pieces along the bluff, leaving the
+refuse everywhere; and it is a necessary consequence that the terrace
+margin, the bluff face, and the talus deposits, places little fitted
+for habitation, should for long distances contain no trace of any
+art shapes save such as pertain to manufacture. Thus are fully and
+satisfactorily accounted for all the turtle backs and other rude
+forms that our paleolith hunters have been so assiduously gathering.
+Nothing can be more fully apparent than that no other race than the
+Indian in his historic character and condition need be conjured up to
+reasonably account for every phase and every article of the recovered
+art. Mistaken interpretations of the nature of shop rejects, and the
+common association of these objects with redistributed gravels, are
+probably accountable for the many misconceptions that have arisen.
+Talus deposits form exceedingly treacherous records for the would-be
+chronologist. They are the reef upon which more than one paleolithic
+adventurer has been wrecked.
+
+Relics of art attributed to gravel man have been collected, so far
+as I can gather from museum labels and from incidental references in
+various publications, from a number of sites aside from the two already
+referred to. These are scattered over the city, and the finds were made
+mostly in exposures of the gravels that remained visible for a short
+time only, as in street and cellar excavations and well pits. These
+reported finds can never be brought within the range of re-examination,
+and the searcher after unimpeachable testimony must content himself
+with placing them in the doubtful column on general principles.
+Urban districts are so subject to disturbance through cutting down
+of hills, filling in of depressions, grading of streets, digging of
+foundations, cellars, sewers, wells and graves that no man can, from a
+limited exposure such as those producing the reported tools necessarily
+were, speak with certainty of the undisturbed nature of the deposits
+penetrated. It is doubtful if any one is justified in publishing such
+observations at all without serious query. Such testimony is liable
+to fall of its own inherent weakness, being absolutely valueless if
+unsupported by collateral evidence of real weight. It can only be made
+permanently available to science by the discovery of something unusual
+or unique with which to couple it, something decidedly un-Indian in
+character or type, as for example the two skulls now in the Peabody
+Museum. These objects and the antler knife-handle exhibited with them
+may be alluded to as the only finds so far made at Trenton, having
+of themselves the least potentiality as proof and these skulls and
+this knife-handle must yet be subjected to the rigid examination made
+necessary by the importance of the conclusions to be based upon them.
+
+Something may now be said concerning the art remains upon which
+this discussion hinges, and upon which conclusions of the greatest
+importance to anthropology are supposed to depend. Let us pass over
+all that has been said with regard to their manner of occurrence and
+association with the gravels and ask them simply what story they tell
+of themselves. Does this story, so far as we are able clearly to read
+it, speak of a great antiquity and a peculiar culture, or does it hint
+rather at vital weaknesses in the position taken by the advocates of
+these ideas? We shall see. The history of the utilization of rudely
+flaked stones in the attempt to establish a gravel man in America
+has never been written, but as read between the lines of paleolithic
+literature, it runs about as follows: The theory of a very rude and
+ancient people, having a unique culture and certain peculiar art
+limitations, was developed in Europe many years ago in a manner well
+known and often rehearsed. This people was associated with the ice age
+in Europe, and this epoch, with its moraines and till and sedimented
+gravels, was found to have been repeated in America. It was the most
+natural thing possible that these discoveries should carry with them
+the suggestion that man may have existed here as in Europe during that
+epoch, and that his culture was of closely corresponding grade. These
+were legitimate inferences and warranted the instituting of careful
+researches, but it was a dangerous suggestion to put into the minds of
+enthusiastic novices with fertile brains and ready pens. The idea was
+hardly transplanted to American soil before finds began to be made. The
+so-called "types" of European paleoliths suggested the lines upon which
+finds here should be made, and everything in the way of flaked stones
+connected directly or indirectly with the glacial gravels which had not
+yet been fully credited to and absorbed by the inconvenient Indian, was
+seized upon as representing the ancient time and its hypothetic people
+and culture. In the early days of the investigation the various rude
+forms of flaked stones, resulting from failures in manufacture, had not
+been studied, and were shrouded in convenient mystery, and they thus
+became the foundation of the new archeologic dynasty in America, the
+dynasty of the turtle-back. Dr. Abbott states in his first work[4] that
+these rude "implements" are not especially characteristic of any one
+locality, but seem to be scattered uniformly over the state. Specimens
+of every type, he says, are "found upon the surface, and are plowed
+up every spring and autumn; but this in no way militates against the
+opinion that these ruder forms are far older than the well-chipped
+jasper and beautifully-polished porphyry stone-work."[5] At that stage
+of the investigation it was not at all necessary that a specimen should
+come from the gravels in place or from any given depth, since the
+"type" was supposed to be easily recognized and was a sufficient means
+of settling the question of age.
+
+[4] Abbott, C. C. The Stone Age in N. J., Sm. Rep. 1875, p. 247.
+
+[5] Ibid, p. 252.
+
+Rude "implements" were called for and they were found. The only
+requirements were that they should not be of well-known Indian types,
+that they should be rude and have some sort of resemblance to what
+were known as paleolithic implements abroad. Since most of these
+so-called gravel implements of Europe are also doubtless the rejects
+of manufacture resemblances were readily found. The early attempts
+to utilize these rejects in support of the theory, and make them
+masquerade creditably as "implements" with specialized features and
+self-evident adaptation to definite ice-age uses, now appear decidedly
+amusing. Gradually, however, the lines have been drawn upon this early
+license, and it is to-day well understood by all careful students, that
+since the rude forms are so often repeated in modern neolithic refuse,
+the only reliable test of a gravel "implement" is its occurrence in
+the gravels in place. That a particular "implement," said to have been
+obtained from the gravels, is of "paleolithic type," does not in the
+least strengthen its claims to being a _bona fide_ gravel implement;
+nor does its easy assignment to a "type" give any additional value to
+the collector's claim that the gravels said to contain it are implement
+bearing. The very names, "rude implement," "paleolithic implement,"
+etc., carry with them a certain amount of mysterious suggestion; one
+thinks of unique, significant shapes and of strange, archaic uses.
+At their mere mention, the great ice sheet looms up with startling
+realism, and the reindeer and the mighty mammoth appear upon the
+scene. The reader of our paleolithic literature is led to feel that
+these antiquated objects carry volumes of history in their worn and
+weather-beaten faces, but this is all the figment of fertile brains.
+These objects have without exception the appearance of the most
+commonplace every-day rejects of manufacture without specialization and
+without hidden meaning. They tell of themselves no story whatsoever,
+save that of the oft-repeated failure of the aboriginal blade maker in
+his struggle with refractory stones. This will be shown with greater
+clearness farther on.
+
+But the scheme does not end with the repetition of a European state of
+affairs. Our gravel archeologists have not been content to adopt that
+feature of the foreign scheme which utterly destroys the paleolithic
+race before a higher culture is brought upon the scene. It was
+thought to improve upon the borrowed plan by allowing for a gradual
+development upward from the paleolithic stage, represented exclusively
+by a class of meaningless bits of flaked stone, through a period less
+rude, characterized by productions so far advanced as to be assigned
+to a definite use. These latter productions consist mainly of rather
+large and often rude blades, sometimes plain, but generally notched or
+modified at the broader end as if to be set in a handle, or attached to
+a spear or arrow shaft. These were assigned to post-glacial times in
+such a way as to bridge or partly bridge the great space between the
+glacial epoch and the present. They were separated arbitrarily from the
+body of the collections of the region, and referred to as probably the
+work of an Eskimo race. This arrangement produced a pleasing symmetry
+and completeness, and brought the history of man down to the beginning
+of the Indian epoch, which is represented by all of those forms of art
+with which the red man is historically associated.
+
+Three principal periods are thus thought to be represented by the
+finds at Trenton; and in the arrangement of the collections these
+grand divisions are illustrated by three great groups of relics, which
+are looked upon by the founders of the scheme as an epitome of native
+American art and culture. By others this grouping is looked upon as
+purely empirical, as an arbitrary separation of the normal art remains
+of the historic Indian, not suggested by anything in the nature or
+condition of the objects, nor in the manner of their discovery.
+
+The "Eskimo" feature of the scheme requires a more detailed examination
+than can be given it here. It may be stated, however, that the
+separation of the so-called Eskimo spear points, or whatever they
+may be, from the great body of associated articles of flaked stone,
+appears to be a highly arbitrary proceeding. That they were extensively
+made by the Indians is proved by the occurrence of refuse resulting
+from their manufacture on modern shop sites, and that they were used
+by the Indian, is equally apparent from their common occurrence on
+modern dwelling sites. The exceptionally large size of the argellite
+points is readily accounted for by the nature of the material. It was
+the only stone of the region well adapted to the manufacture of long
+blades or projectile points. Jasper, quartz and flint have such minute
+cleavage that, save in rare cases, small implements only could be
+made from them. Their peculiar manner of occurrence, described at so
+much length by Dr. Abbott,[6] has been given undue consideration and
+weight. The phenomena observed may all be accounted for as a result of
+the vicissitudes of aboriginal life and occupation within the last few
+hundred years as fully and satisfactorily as by jumping thousands of
+years backward into the unknown.
+
+[6] Abbott, C. C. Popular Science Monthly, Dec., 1889.
+
+Whatsoever real support there may be for the "Eskimo" theory, either in
+the published or the unpublished evidence, it is apparent that under
+the present system of solitary and inexpert research, the scientific
+world will gain little that it can utilize without distrust and danger.
+Whatsoever may be the final outcome--which outcome is bound to be the
+truth--it is clear that there is little in the present evidence to
+warrant the separation of a "paleolithic" and an "Eskimo" period of art
+from that of the Indian.
+
+That the art remains of the Trenton region are essentially a unit,
+having no natural separation into time, culture or stock groups,
+is easily susceptible of demonstration. I have already presented
+strong reasons for concluding that all the finds upon the Trenton
+sites are from the surface or from recent deposits, and that all may
+reasonably be assigned to the Indian. A find has recently been made
+which furnishes full and decisive evidence upon this point. At Point
+Pleasant, on the Delaware, some twenty-five miles above Trenton, there
+are outcrops of argillite, and here have been discovered recently the
+shop sites upon which this stone was worked. There are two features
+of these shops to which the closest attention must be given. The
+first is that they are manifestly modern; they are situated on the
+present flood plain of the Delaware, and but a few feet above average
+water level, the glacial terrace here being some forty or fifty feet
+in height. These shops, therefore, represent the most modern phases
+of aboriginal industry, and may have been occupied at the coming of
+William Penn. The second point is that every type of flaked argillite
+found in the Trenton region, associated with the gravels or otherwise,
+is found on this site. It was to a certain extent a quarry site, for
+the great masses of argillite brought down by the floods were here
+broken up and removed from the river banks or bed. It was a shop site,
+for here the articles, mainly blades, were roughed out, and it was
+also a dwelling place--a village site--where all the specialized forms
+of flaked stones made from the blades were prepared for use. Here are
+found great numbers of the rude failures, duplicating every feature
+of the mysterious "paleolith" with which our museums are stocked,
+and exhibiting the same masterly quitting at just the point "where
+no further shaping was possible."[7] Here we see the same boldly
+manipulated "cutting edge," the "flat bottom" and "high peak," and the
+same mysteriously weathered and disintegrated surfaces, so skillfully
+made, by a nice balancing of accidents,[8] to tell the story of
+chronologic sequence in deposition.
+
+[7] Abbott, C. C. Smithsonian Report, 1875, p. 248.
+
+[8] Ibid. Primitive Industry, p. 487.
+
+Beside the failures, we have here, as on other quarry shop sites, the
+evidence of more advanced work, the wide, thick, defective blades, and
+many of the long, thin blades broken at or near the finishing point.
+Here, too, just back of the roughing-out shops, are the dwelling sites
+from which many specialized forms are obtained. The "Eskimo" type
+is fully represented as well as the ordinary spear point, the arrow
+point, and the perforator of our Indian. There is not a type of flaked
+argillite known in the Delaware valley that may not be duplicated
+here on this modern Indian site, and this has been known by local
+archeologists for years. Why so little has been said about the matter
+is thus explained. Dr. Abbott, in 1890, discovering this site, and
+finding "typical paleolithic implements" (the ordinary ruder forms of
+rejects) among the refuse, was so entirely at a loss to explain the
+occurrence that he felt compelled to again "take up the examination
+of the gravel deposits of the valley of the Delaware" with the hope
+of "finally solving the problem."[9] The true conditions would have
+been at once apparent to any one not utterly blinded by the prevailing
+misconceptions.
+
+[9] Abbott, C. C. Annual Report of the Curator of the Museum of
+American Archeology, University of Pennsylvania. No. 1, p. 7.
+
+The entire simplicity of the archeologic conditions in the Delaware
+valley may be further illustrated. Had William Penn paused in his
+arduous traffic with the tawny Delawares, and glanced out with
+far-sighted eyes from beneath the pendant branches of the great elm
+at Shackamaxon, he might have beheld an uncouth savage laboriously
+fabricating rude ice age tools, making the clumsy turtle-back, shaping
+the mysterious paleolith, thus taking that first and most interesting
+theoretical step in human art and history. Had he looked again a few
+moments later he might have beheld the same tawny individual deeply
+absorbed in the task of trimming a long rude spear point of "Eskimo"
+type from the refractory argillite. If he had again paused when another
+handful of baubles had been judiciously exchanged, he would have seen
+the familiar redskin carefully finishing his arrow points and fitting
+them to their shafts preparatory to a hunting and fishing cruise on the
+placid Delaware. Thus in a brief space of time Penn might have gleaned
+the story of the ages--the history of the turtle-back, the long spear
+point and their allies--as in a single sheaf. But the opportunity was
+wasted, and the heaps of flinty refuse left upon the river bank by the
+workmen were the only record left of the nature of the work of that
+day. Two hundred years of aboriginal misfortune and Quaker inattention
+and neglect have resulted in so mixing up the simple evidence of
+a day's work, that it has taken twenty-five years to collect the
+scattered fragments, to sift, separate and classify them, and to assign
+them to theoretic places in a scheme of culture evolution that spans
+ten thousand years.
+
+Yet is there really nothing in it all, in the theories, the
+observations, the collections and the books? Do I speak too positively
+in condemnation of the results of years of earnest investigation?
+Perhaps so, but the voluminous testimony is so overloaded with
+inaccuracies, the relics of unscientific method and misleading
+hypotheses, that every item must be sharply questioned; and the
+conclusions reached so far overstep the limits warranted by the
+evidence, that heroic measures alone can be effectual in determining
+their exact value. If, as many believe, vital errors have been
+embodied in the evidence presented by the advocates of the theory,
+it is impossible to state the case too strongly. Error once fully
+absorbed into the literature of science has many advantages over the
+tardy truth; it is strongly fortified and must be attacked and exposed
+without fear or favor. Truth involved with it cannot permanently
+suffer. If the twin theories of a gravel and a paleolithic man in
+eastern America are to be assailed as unsound or as not properly
+supported, it should be done now while the originators and upholders
+are alive and alert to sustain their positions or to yield to the
+advances of truth. I do not wish to wrongly characterize or to unduly
+minimize the evidence brought to bear in favor of these theories. I do
+intend, however, to assist the world so far as possible in securing an
+exact estimate of all that has been said and done, and all that is to
+be done.
+
+In a previous article I have examined the evidence relating to
+paleolithic art in the eastern United States, and have indicated
+its utter inadequacy and unreliability. In this paper the testimony
+relating to the occurrence of gravel art, in the locality most fully
+relied upon by advocates of the theory, has been partially reviewed
+and subjected to the strong light of recent observations. It is found
+that the whole fabric, so imposing in books and museums, shrinks away
+surprisingly as it is approached. The evidence furnished by the bluff
+face and by the railway cutting, the two leading sites, is fatally
+weakened by the practical demonstration of the fact that the gravels
+proper are at these points barren of art remains. In endeavoring to
+naturalize an immigrant hypothesis, our gravel searchers, unacquainted
+with the true nature of the objects collected and discussed, and little
+skilled in the observation of the phenomena by means of which all
+questions of age must be determined, have undoubtedly made grievous
+mistakes and have thus misled an expectant and credulous public.
+
+The articles themselves, the so-called gravel finds, when closely
+studied are found to tell their own story much more fully and
+accurately than it has heretofore been read by students of archeology.
+This story is that the art of the Delaware valley is to all intents and
+purposes a unit, that there is nothing unique or especially primitive
+or ancient and nothing un-Indian in it all. All forms are found on
+demonstrably recent sites of manufacture. The rude forms assigned
+by some to glacial times are all apparently "wasters" of Indian
+manufacture. The large blades of "Eskimo" type are only the larger
+blades, knives and spear points of the Indian, separated arbitrarily
+from the body of the art-remains to subserve the ends of a theory,
+certain obscure phenomena of occurrence having been found to give color
+to the proceeding. To place any part of this art, rude or elaborate,
+permanently in any other than the ordinary Indian category will take
+stronger proofs than have yet been developed in the region itself.
+
+The question asked in the beginning, "Are there traces of glacial man
+in the Trenton gravels?" if not answered decisively in the negative,
+stands little chance, considering present evidence, of being answered
+in the affirmative. In view of the fact that numerous observations
+of apparent value have been made in other sections, there is yet
+sufficient reason for letting the query stand, and we may continue to
+cherish the hope that possibly by renewed effort and improved methods
+of investigation, something may yet be found in the Trenton gravels
+clearly demonstrative of the fascinating belief in a great antiquity
+for the human race in America.
+
+The evidence upon which _paleolithic man_ in America depends is so
+intangible that, unsupported by supposed analogies with European
+conditions and phenomena, and by the suggestions of an ideal scheme
+of culture progress, it would vanish in thin air; and if the theory of
+a _glacial man_ can summon to its aid no better testimony than that
+furnished by the examples examined in this paper, the whole scheme,
+so elaborately mounted and so confidently proclaimed, is in imminent
+danger of early collapse.
+
+                                                        =W. H. Holmes.=
+
+
+
+
+GEOLOGY AS A PART OF A COLLEGE CURRICULUM.
+
+
+The demand for scientific studies as a part of the college curriculum
+is felt by all those who have to do with the provision of higher
+instruction for American youth. The reasons for this may be various,
+but a fundamental reason is found in the tendency among the American
+people in particular, and in this age in general, toward practicality
+in all things. Applied to education this practicality asks for a
+training which shall have a direct bearing upon the business of life to
+be followed immediately after the training period is ended. It means
+a differentiation of subjects and specialization in methods to adjust
+the education to the different functions which the students taking it
+are preparing for. It calls for a professional education for those
+who expect to become lawyers, doctors, ministers, or teachers,--a
+technical education for those who are to engage in the arts of the
+mechanical or civil engineer, or of the architect. It results not only
+in the establishment of colleges and universities devoted to this
+kind of education, but it affects the methods of the high schools and
+academies, and is felt down to primary schools, and on the other hand
+the older institutions founded on a different plan are adapted to the
+popular demand by the addition to the regular studies of "electives,"
+chosen not always for their value or disciplinary studies, but because
+of the practical applicability of the information to be derived from
+them, to the business of the student.
+
+Without discussing the relative merits of the two ideas of education,
+the chief contrast between them may be found in the character of the
+results sought. The knowledge of things and their uses is of chief
+importance in the practical education; the knowledge of ideas and skill
+in their use is the aim of the liberal education. Geology is one of the
+sciences which most men will at once classify as among the practical
+sciences. It deals with matters of practical importance to everybody.
+Coal, iron, the metals, silver, gold, tin, lead, building stone, sand,
+clay, petroleum, and natural gas, and all geological products are
+essential materials of modern civilization, and a knowledge of them
+and of their modes and places of occurrence is one of the requisites
+of an education, either from the practical or the liberal point of
+view. So too the dynamics of atmospheric and hydraulic erosion, the
+agency of rivers and oceans in destruction, removal and reconstruction
+of geological formations have their eminently practical bearings upon
+the various arts of engineering. While the practical value of geology
+is thus evident and undisputed, it is not on this account that its
+importance as a part of a college course of education is urged. As
+a practical study geology becomes the centre of a group of studies
+requiring years for mastery. Chemistry and physics are primarily
+essential to a full understanding of the most common of geological
+problems. And to use geological facts and phenomena, an acquaintance
+with the complex methods of engineering, civil and mechanical, which
+again call for a thorough mastery of mathematics, is necessary.
+Mineralogy and petrography, metallurgy and mining engineering have
+each reached a stage of development entitling them to the rank of
+separate sciences, but the practical training of the geologist should
+include them all. When we add the biological sciences connected with
+historical geology, paleontology, zoölogy and botany, with all the
+laboratory and field work required for their proper study, we have a
+group of affiliated branches of learning requiring four or five years
+of continuous study after the student has learned how to study. It is
+plain therefore that only a specialist, one who is willing to neglect
+other studies, or who has previously had a liberal training, can
+perfect himself on the practical side in the science of geology.
+
+But irrespective of its practical uses, as a means of training and
+supplementary to the ordinary studies of a college curriculum, geology
+is one of the most useful of the sciences of observation. It is
+in providing that particular training to which President Eliot has
+recently called attention in the _Forum_ (Dec., 1892, Wherein Popular
+Education Has Failed), that geology can be used to such advantage.
+Speaking particularly of the lower education, President Eliot says
+it is "the judgment and reasoning powers" that particularly require
+attention. Their systematic development is to be attained in the four
+directions of "observing accurately, recording correctly, comparing,
+grouping and inferring justly, and expressing cogently the results of
+these mental operations." (p. 421.) The attainment of these ends is
+one of the purposes of liberal education, whether it be in the primary
+school or in the university. And geology, or any other science, is
+of value in a college course in proportion to its fitness for the
+exercise and development of these functions of the student. Geology may
+be taught without regard to these ends, and then it is valuable from
+the practical point of view, but when we examine it in respect of its
+availability as a disciplinary study we find it offering particular
+attractions.
+
+Using the distinction between theory and practice, which is as old
+as Aristotle, geology in its theoretical aspect is more easily
+comprehended than is the theoretical aspect of most of the modern
+sciences. This arises first from the fact that the facts and phenomena
+are of a simple and grand nature, making it possible for the teacher
+to direct certain attention to the specific facts under consideration.
+The water of the rivers, the mud by the road side, the rocks and sands
+on the shore are familiar objects to all, and it is a simple matter to
+call attention by ordinary language to the specific facts regarding
+them, which, analyzed out, are to form the basis of exact ideas and
+scientific definition and classification. Geology is the one science
+among the natural sciences which may begin with the common language
+of the pupil, and by means of such language alone may build up ideas
+of precise phenomena in scientific terms. Physiography or physical
+geography surpasses geology proper in this particular, as the admirable
+work of Professor Davis is showing, and on this account it is the best
+introduction to geology. But the very largeness and indefiniteness
+of the facts are in the way of the use of physical geography for the
+exercise of the finer and more exact functions of observation. The
+disciplinary value of classics and mathematics is to a considerable
+extent derived from this quality, the precision with which the words
+or figures kindle like ideas. So long as the object of the training
+is to teach the knowledge of ideas and how to use them, classics and
+mathematics are the simplest and purest means of developing a liberal
+education. The addition of sciences to the college course is not
+because of the usefulness of the knowledge of things thus to be gained,
+but because the language of the sciences is essential to call forth the
+observation and the exercise of the accompanying mental operations.
+
+When it comes to dealing with the ideas associated with particular
+sense-observation, where form or motion can not be expressed in
+simple mathematical terms, language can not communicate a new idea
+or kindle it in another mind with precision. It is necessary by some
+means to recall or to present the object itself to the student. In
+the teaching of science this point is of great importance, and much
+of the unsatisfactoriness of science-teaching is doubtless due to
+failure to note it. No circumlocution of words can arouse in another
+or communicate to him the idea appropriate to a sensation he has never
+felt. The blind man whose eyes are opened sees men as trees walking.
+
+In the use of science for elementary training (and the training
+is elementary until the student is capable of investigating and
+interpreting the facts and phenomena of a science directly) that
+science is the better which deals with objects which are simple, common
+and easily observed. Such is geology in some of its aspects. Every time
+the student walks in the country he sees the facts discussed in the
+text-book or by his teacher; and from attention to those with which he
+is already familiar he can be readily led to observe and give attention
+to others and to analyze those already in his mind by properly directed
+questions.
+
+In the field of geology are found the ready means for the exercise
+and development of observation and thought. The learner begins
+with ideas which every intelligent mind associates with the objects
+described or named, and by degrees the marks of his knowledge are
+increased, the relations of things are grasped, and the content of his
+ideas associated with the language of his science is enlarged. In the
+process of learning the science he has been building up his stock of
+knowledge of facts and phenomena, but, of more importance than that,
+he has learned the method of observing and of scientific thinking.
+He has had training in the methods of reducing the hard facts of
+nature to the laws of thought and practice, he has seen the method by
+which theoretical order is made out of the interminable confusion and
+complexity of natural things.
+
+Beside this primary reason for the use of geology as a disciplinary
+science-study, there is a second reason arising from the symbolic
+nature of a large group of its facts. This aspect of the science is
+best seen in the historical and stratigraphical parts of geology, in
+which fossils are the chief data for study. The interpretation of a
+fossil into a species of organism, having its definite place in the
+elaborate classification of the zoölogist, or as an indicator of
+the time and place and mode of formation of the strata in which it
+is buried, is, to be sure, a most intricate and, at first thought
+it would seem, an unattractive process. But no more so, I would
+say, than the interpretation of a series of Greek characters. The
+interpretation of the Greek reveals to us the richest results of human
+thought and most perfect laws of human speech, and we find therefore
+in the analysis required the most perfect discipline of the powers
+of speech and language. The fossil too holds, ready to be revealed,
+the story of the history of the world and the laws of the evolution
+of the organic life of the globe, and records an inexhaustible wealth
+of information regarding the laws of nature. But as an instrument of
+intellectual discipline its great merit lies in its symbolic nature.
+It is this symbolic character of the classical languages and of the
+mathematics which fits them to be universal means of liberal training.
+The symbolic nature of the fossil fits it to become the exponent of
+training in the pure science of nature. The fossil is a mark which
+stands for something, and thus, in the nature of things, it asks
+for interpretation. As a symbol it stimulates minute and accurate
+observation, and kindles close and exhaustive thought; as a symbol it
+leaves us the ideas it has engendered after it is lost to memory as
+an observation. Thus the value of its study does not depend upon the
+retention in the memory of the facts brought before the mind, but in
+the training of the mental processes required in its interpretation.
+The study of this branch of geology exercises and develops all the
+faculties which are specially exercised in any scientific investigation.
+
+Another aspect in which it is an ideal means for such training comes
+from the fact that it is equally valuable at every stage of progress
+of the student. When first examined it means nothing to him. He knows
+nothing of organism, of strata, of geological time. The fossil gains
+meaning only as he is able to put meaning into it. The student must
+ask questions, and as step by step he answers his questions by more
+minute and wider examination, the fossil holds a fuller interpretation.
+His studies lead him to investigation of the whole field of nature,
+the rocks, the formation of deposits, the action of the elements, the
+conditions of life, the forms of organism, their functions and habits,
+the laws of growth, their adaptation to environment, the changes of
+events in time, the efforts of association and struggle for life, the
+principles of evolution and development--the migration and origin and
+extinction of organisms on the globe. Nothing in nature is without
+interest to him. Further than this the amount of good he gains is not
+measured by the number of fossils he studies, but by the wideness of
+his research. A handful of fossils from some one fossiliferous ledge
+may be the text for a year's study, and the methods acquired in the
+study may be the nucleus of a life's work. In this department of
+geology the possibilities for new discoveries, new developments of
+science are almost endless. As a single author thoroughly read develops
+a wealth of knowledge of the laws of language and thought, so geology
+may be studied by the use of a limited set of its phenomena and become
+the introduction to the exhaustive study of natural science.
+
+Another advantage attaching to geology as a science-study for the
+college curriculum, arises from the fact that it may be pursued deeply
+without the elaborate aid to the senses required in other sciences
+for making minute record or measurement of facts or phenomena. As in
+language and mathematics, it is essential to acquire a familiarity
+with the grammar, the dictionary and the symbols, formulas and rules
+of their usage before the finer training in the use of thought begins,
+so the vocabulary and the definitions of a science must be acquired
+before much use can be made of the higher discipline to be derived from
+scientific study. In language study this higher training comes from
+practice in making the minute analysis, in detecting the fine shades
+of meaning expressed in the literature itself. So it is important in
+selecting a science to be used as a disciplinary study that the facts
+and laws of nature with which it is concerned should be capable of
+clear and precise definition, and, moreover, that it should furnish a
+field for the study of the minute and intricate relationship existing
+between the different facts which are to be attained by personal
+inspection of the objects themselves. In most of the sciences this
+deeper exercise of scientific thought requires for its successful
+pursuit artificial aids to the common senses of observation. Chemistry
+must have its purified acids and reagents, test tubes, and delicate
+scales for measurement of weight and volume. Mineralogy must have its
+chemical analyses, or optical measurements so fine that microscopes
+of highest power are essential tools for the investigation. Physics
+must have the most delicate measurements of time and space and weight.
+Botany, for the earlier stages of study, is fully equal to geology in
+these respects, but its scope is much less general. Zoölogy requires
+dissections calling for skill in manipulation, and in other respects
+is ill adapted to general classes. But precision in the intellectual
+processes of observation and reasoning can be cultivated in the use of
+geological facts to their highest and widest perfection, with scarcely
+any aids to the normal faculties of observation. A couple of hammers,
+a pocket lens, a chisel and a few pointed steel tools for revealing
+fossils, a tape line, compass and clinometer are the few equipments
+that will enable the geologist to carry his investigations to almost
+any degree of thoroughness.
+
+What has already been said applies to the study of the pure science
+of geology either in the field or in the laboratory. There is
+still another use to which this, as other sciences, may be put in
+disciplining the college student in directions not provided for by
+literary or mathematical studies,--the study of man as an investigator.
+In the pursuit of the study of geology, the first instruction must be
+received in didactic form, but after the text-book and lecture stage
+is passed, or while it is under way consultation of the literature
+of the sciences is appropriate. In the use of scientific literature
+the critical judgment is brought under training, and the varying
+interpretations of well known phenomena by expert scientists suggest
+the prominent part which the notions already in the mind play in
+the interpretation of the external facts observed. The experienced
+geologist will recall many cases of honest report of impossible facts
+by men who are unable to distinguish between what they saw and the
+false interpretations they made of these observations. One man will
+report that a live toad jumped out of the middle of a solid piece of
+coal, when it was heated in the stove; another will swear that he saw
+a fossil shark's tooth taken out of a ledge of Trenton limestone.
+It is evident that our memory of observation is not the revival of
+the object producing the sensation, but of the idea we framed of the
+sensation at the time. The study of original descriptions of objects of
+nature reveals the fact that the describer uses the ideas he already
+has in his mind as he does the standard foot-rule in his hand for
+measuring that which he describes, and it is by the study of scientific
+literature and the comparison of views of many scientists that this
+highest discipline of the observational faculties is attained--the
+power to determine the personal equation of error for the observer,
+and thus see through his descriptions a truer representation of the
+facts than the observer himself saw. Geological literature is admirably
+adapted for this higher discipline, and in no field of science (I think
+not in astronomy itself), has wider and more comprehensive thought been
+applied than in geology. While other branches of science have been
+developed and become more narrow and special in their treatment of the
+facts concerned, geology still stands as the most comprehensive of all
+the sciences of nature.
+
+                                                        H. S. Williams.
+
+  =Yale College=, November 30, 1892.
+
+
+
+
+THE NATURE OF THE ENGLACIAL DRIFT OF THE MISSISSIPPI BASIN.
+
+
+It is of some importance, both to the practical work of the field
+and the theoretical deductions of the study, to determine the nature
+and amount of the drift that was carried forward in the body of the
+ancient continental glaciers, and brought out on their terminal slopes
+and at length deposited at their frontal edges, and to distinguish it
+from that which was pushed or dragged or rolled along at the bottom of
+the ice.[10] It may be helpful to indulge in a speculative discussion
+at the outset to prepare the way for the specific evidence and the
+inferences to which it leads.
+
+[10] Debris, which may be imbedded in the basal layer of the ice
+during some part of its transportation, but which is brought down to
+the bottom and subjected to basal action in the latter part of its
+course, and ultimately becomes a part of the basal deposit, is not here
+included in the englacial drift.
+
+Whenever a prominence of rock is overridden and enveloped by a
+glacier of the free-moving continental type, one of two things takes
+place; either that part of the ice which passes over the summit of
+the prominence flows down its lee slope, carrying whatever debris it
+dislodges down to the rear base, and thence onward along the bottom
+of the ice, or else the currents which pass on either side of the
+prominence close in behind it before the corresponding current which
+passes over the summit reaches the point of their junction, in which
+case the summit current is forced to pass off more nearly horizontally
+into the body of the ice, carrying with it whatsoever debris it has
+dislodged from the summit of the prominence and embodied within its
+base. The law of the phenomena appears to be that whenever the height
+of the prominence is less than one-half the base, measured transversely
+to the movement of the ice, the summit current will follow down the lee
+slope; but whenever the height of the prominence is more than one-half
+the transverse base, the lateral currents will close in on the lee,
+and the summit current will flow off into the body of the ice. This
+simple law is, however, subject to very considerable modifications from
+several different sources which may be grouped under (1) differences
+in the friction arising from basal contact, and (2) differences of
+internal friction and mobility. The lateral currents will expose more
+surface to the sides and base of the hill and the adjoining plain, and
+will be more subject to conflicting currents, while, on the other hand,
+being deeper currents, they will presumably be more fluent. These and
+other qualifying conditions will go far to vitiate the application
+of the law, but its statement may have some value as representing a
+general conception of the phenomena. When the height of the prominence
+becomes great relative to the total thickness of the ice, the fluency
+of the summit current may be much reduced relative to that of the
+central parts of the lateral currents. When the prominence reaches the
+surface, blocks dislodged from it are borne away on the surface of the
+glacier, and constitute superglacial drift. Blocks dislodged from near
+the summit, but below the surface of the ice, are presumably carried
+onward in the upper zone of the glacier; while other blocks detached
+at various but sufficient heights on the side of the prominence are
+doubtless borne around into the lee and carried forward in the same
+vertical plane as the summit stream, so that there comes to be a
+vertical zone set with boulders moving on from the lee side of the
+nunatak.
+
+Lofty ledges or plateaus, with vertical or undercut faces, furnish
+similar means for the lodgment of debris within the body of the ice.
+
+In these and doubtless in other ways it appears that there came to be
+lodged directly within the body of the Pleistocene glaciers at some
+considerable distances above their bases, blocks derived from rock
+prominences that rose with sufficient steepness above the general
+surface of the country over which the ice passed. The lodgment of
+debris on the lateral borders of glaciers is neglected here because
+it has little or no applicability to the phenomena of the upper
+Mississippi basin. It is also doubtful whether any prominences
+protruded through the ice except near the thin edge, when advancing and
+retreating, and these are too inconsiderable to merit attention.
+
+It is obvious, upon consideration, that blocks detached from summits
+or from the sharp angles of out-jutting ledges or plateaus might
+suffer some glacial abrasion in the process of their dislodgment and
+transposition along the crest or projecting angle, but that in general
+such abrasion would be small, and, in most cases, nearly or quite
+absent. The debris so incorporated in the body of the ice would be,
+for the most part, angular, and, as it was brought forward in the ice,
+it would probably suffer very little abrasion. If it continued to move
+forward in the plane in which it started, descending only so much as
+the bottom wastage of the ice required, it would be brought out to
+the terminal slope of the ice sheet by virtue of the melting away of
+the ice above, and thence it would be carried on down the terminal
+slope as superglacial debris, and dropped at the frontal edge. If this
+be the true and full history, there would be no commingling of this
+englacial matter with the subglacial debris. It is evident, that the
+englacial matter brought forward from the crest of one prominence would
+be intermingled with that brought forward from other prominences lying
+in a line with it, or lying so near it that the lateral spreading of
+the debris would lead to commingling. It is also clear that variations
+in the direction of currents would tend to the same result, so that
+englacial matter from different prominences of the same general region
+might be commingled. So also englacial material, by crevassing and by
+the descent of streams from the surface to the base, would be carried
+down to the bottom and mingled with the subglacial debris. So also
+blocks broken away from the base of the prominence which yielded the
+englacial erratics might be moved forward along the bottom parallel
+with the englacial material above, and lodged at any point along the
+line. It is therefore to be expected that the basal deposits will
+contain the same rock species as the englacial, but if there be no
+process by which the basal material is carried upward the reverse will
+not be the case, and there will be a clear distinction between the
+englacial deposit and the subglacial deposit, in composition as well as
+physical state.
+
+Not a few glacialists, however, advocate in somewhat differing forms
+and phases the doctrine that basal material is carried upward into
+the body of the glacier and at length reaches the surface, and that
+at the extremity of the ice this is commingled with any erratics that
+may be englacial or superglacial by original derivation. This doctrine
+appears to have had its origin in the endeavor to explain the very
+common fact that glacial drift has been carried from lower to higher
+altitudes. Erratics are often found lodged several hundred feet higher
+than the outcrop from which they were derived. It has never seemed to
+me, however, that this phenomenon necessarily was different in kind
+from that which takes place in the bottom of every stream; at least I
+have not come in contact with any instances that seemed to require a
+different explanation, except those connected with kames and eskers
+that require a special explanation in any case. We are so accustomed
+to view streams from above, and so accustomed to study the extinct
+glaciers from the bottom, that we are liable to overlook the community
+of some of the simpler processes involved alike in both phenomena. The
+dictum that water never runs up hill is measurably true of the surface
+currents of the ice as well as water, but it altogether fails when
+applied to the basal currents of either. It is probable that there is
+no natural stream of any length in which, at some part of its course,
+basal debris is not carried from lower to higher altitudes and lodged
+there. If the bed of any stream were made dry and the debris in it
+critically examined, it would be found that at numerous points the
+silts or sands or gravels had been carried from the bottom of some
+basin in its bed to the higher rim or bar or reef that bordered it
+on the downstream side. So I conceive that, on a grander scale, the
+natural result of the flow of the basal ice of a continental glacier
+over the inequalities of the country was the lifting of material from
+some of the lower horizons and its lodgment on the crests of ridges or
+the slopes or summits of mountains that lay athwart its course.
+
+So again, it is certain that a considerable part of the peripheral
+drainage of glaciers takes place through tunnels beneath the ice.
+It is reasonable to suppose that during the winter season, when the
+drainage is slack, these tunnels tend to collapse in greater or less
+degree, under the continued pressure of the ice and the "fattening" of
+the glacier, so that in the early part of the next melting season the
+contracted tunnels may be over-flooded by glacial waters. To the extent
+that these tunnels become incompetent the water would become ponded
+back in the crevasses and moulins by which the surface-water gains
+access to them. They thus come to have something of the force of water
+flowing in tubes, and may be presumed to be capable of forcing rounded
+material to some considerable height, and of carrying ice-imbedded
+boulders to any point reached by the stream. These tunnels probably
+undulate with the bottom, and lodgment along them takes place wherever
+enlargement permits.
+
+Without, therefore, appealing to any upward cross currents within
+the ice itself, it is possible to explain the transportation of the
+drift from lower to higher altitudes. I have never seen phenomena of
+this kind that seemed to call for any other explanation than these. I
+am not prepared to say that there are no such phenomena. One of the
+purposes of this article will have been accomplished, if it shall call
+forth a critical statement of phenomena that require the assumption
+of internal upward movements of the ice to account for them, and of
+the criteria which distinguish such phenomena from those that may be
+referred to upward basal movements such as are common to all streams
+or to the exceptionally conditioned subglacial streams. That there are
+upward internal movements in most streams is as much beyond question
+as the existence of upward basal currents in rivers and glaciers, but
+they are dependent chiefly upon the velocity of the current and the
+irregularity of the bottom. Theoretically, as I understand, a stream
+moving in a straight course on a perfectly smooth bottom would not
+develop an upward cross current. Each lower layer would move slower
+than that above it by reason of basal friction, but they would move
+on in parallel lines. But if irregularity of bottom be introduced the
+parallelism is obviously destroyed, and if the velocity be high so that
+the momentum of the particles becomes great relative to their cohesion,
+irregular internal movements will result, and these will often be of a
+rotary nature in vertical planes bringing the basal parts of the fluid
+to the surface or the reverse. For this reason rapid streams abound in
+rotary currents, while slow streams do not.
+
+Now it is quite obvious that a stream of water moving at a rate of
+three or four feet per day, or even fifty or sixty feet per day, would
+not develop perceptible upward currents, and certainly would not
+lift the lightest silt from its bottom. I do not think there are any
+theoretical grounds for believing that internal glacial currents are
+developed, which flow from base to surface, carrying bottom debris to
+the top.
+
+One of the most remarkable expressions of the drift phenomena of the
+Upper Mississippi region consists of belts of boulders stretching
+for great distances over the face of the country, and disposing
+themselves in great loops after the fashion of the terminal moraines
+of the region with which they are intimately connected. Besides this,
+there are numerous patches of boulders of more or less irregular form
+and uncertain relations. The whole of these have not been studied
+in detail, but a sufficient portion of them have received careful
+examination to justify the drawing of certain conclusions from them.
+Those which have been most studied lie in Ohio, Indiana, Illinois,
+Michigan, Wisconsin, Iowa and Dakota. Those of the first three States
+have been most carefully traced and their constitution is such as to
+give them the greatest discriminative value. To these our discussion
+will be limited chiefly.[11]
+
+[11] Parts of these tracts were long since described by Bradley of
+the Illinois Survey. (Geol. Surv. Ill., Vol. IV. p. 227). Collet of
+the Indiana Survey (An. Rep. 1875, p. 404) and Orton and Hussey of
+the Ohio Survey (Geol. Surv. Ohio, Vol. III., pp. 412, 414 and 475).
+The relationship of these tracts to morainic lines and to each other
+I worked out some years since (Third An. Rep. U. S. G. S. pp. 331,
+332, 334) but I owe many details and some important additions to my
+associate, Mr. Leverett.
+
+Emerging from the dunes at a point north of the Iroquois river in
+Jasper county, northwestern Indiana, a well characterized belt of
+surface boulders stretches westward to the State line, just beyond
+which it curves about to the south and then to the east, and re-enters
+Indiana a little south of the northwest corner of Benton county. It
+soon turns abruptly to the south and reaches the Wabash river near the
+centre of Warren county. The immediate valley of the Wabash is thickly
+strewn with boulders from the point where the belt reaches it to the
+vicinity of West Point on the western line of Tippecanoe county. The
+uplands, however, do not give any clear indication of the continuity
+of the belt, and the connection is not altogether certain. There is an
+inner well-marked belt that branches away from this in the central part
+of Benton county and runs southeasterly into the northwestern quarter
+of Tippecanoe county, beyond which only scattered boulders occur, which
+leaves its precise connections also in doubt. But starting from West
+Point, which is less than a dozen miles from the point where the two
+belts cease to be traceable with certainty, a well-defined belt, one
+or two miles wide, runs southeasterly across the southwestern corner
+of Tippecanoe county and the northeastern quarter of Montgomery county
+to the vicinity of Darlington, beyond which its connection is again
+obscure, although boulders occur frequently between this point and the
+northwestern corner of Brown county, where boulders are very abundant.
+So also, patches of exceptionally abundant boulders occur in the west
+central part of Clinton county. These may be entitled to be regarded
+as a connecting link between the train which enters northwestern
+Tippecanoe county and that of northwestern Boone county, as scattered
+boulders of the surface type, but of not very exceptionally frequent
+occurrence, lie between them. However this may be, a belt of much
+more than usually frequent surface boulders stretches southeasterly
+to the vicinity of Indianapolis, and probably connects with a very
+well-marked belt lying near the south line of the southeast quarter
+of Marion county and in the northeastern part of Johnson county.
+There is also a well-defined tract in southeastern Hendricks county,
+running east and west, without evident connection with the foregoing
+tracts, though it may be the equivalent of the Darlington belt. There
+is also a somewhat unusual aggregation in the form of irregular belts
+in southeastern Johnson county, in the vicinity of Nineveh, and in
+southern Shelby county. The belt south of Indianapolis is probably to
+be correlated by scattered boulders only slightly more abundant than
+those of the adjacent region, but of the surface type, stretching
+northeasterly to near the center of the west half of Henry county,
+where a well-marked belt again sets in. From this point the tract runs
+northeasterly nearly to the north limit of the county, where it turns
+easterly and runs in the vicinity of the line between Randolph and
+Wayne counties to near the Ohio line, where it curves to the southeast
+entering Ohio near the northwest corner of Preble county. In its
+southeasterly course across that county it is phenomenally developed as
+has been well shown by the descriptions of Professor Orton. Soon after
+entering Montgomery county it curves about to a northeasterly course,
+and crossing the great Miami river, a few miles above Dayton, holds
+its northeast course across the southeastern part of Miami county,
+the northwestern part of Champaign county, and thence on to about the
+center of Logan county, where it curves about and runs in a direction a
+little east of south to near the southeast corner of Champaign county,
+beyond which it ceases to be a specially notable phenomenon.
+
+In the region between the Wabash and Kankakee rivers, in northern
+Indiana, there are numerous tracts of irregular form over which surface
+boulders in phenomenal abundance are scattered. These are particularly
+noticeable in southern Jasper county; in the vicinity of Wolcott, Monon
+and Chalmers in White county; near Star City in Pulaski county; in
+the southeastern corner of Stark county, and very generally along the
+great interlobate moraines, lying parallel with the Eel river, and
+some others of the Saginaw glacial lobe. These are so associated with
+the inter-tangled morainic phenomena of that region as not to admit of
+convenient and brief description in their genetic relationships.
+
+The well-defined tracts have a most significant distribution. The first
+part described is associated with the terminal moraine that marked
+the margin of a lobe of ice that moved westward along the axis of the
+Iroquois basin to a point a few miles beyond the Indiana-Illinois line.
+The portion that runs southward to the Wabash is associated with the
+moraine that follows the same course, and runs at right angles over the
+older moraines of the Lake Michigan lobe. The tract in Tippecanoe and
+Montgomery counties, that in south Marion county, and that in Henry and
+Randolph counties, in the eastern part of the state, are associated
+with the terminal moraines that form a broad loop with the West White
+river basin lying in its axis. In western Ohio the belt is intimately
+associated with a moraine that bordered the Miami lobe of the ice
+sheet, and the south-trending portion in eastern Logan and Champaign
+counties lies on the western margin of the Scioto lobe.
+
+The relationship of these tracts to terminal moraines is very clear and
+specific. They constitute marginal phenomena of the ancient ice sheet.
+Their distribution completely excludes their reference to floating ice,
+for they not only undulate over the surface utterly negligent of any
+horizontal distribution, but they are disposed in loops in crossing the
+basins of the region, and the convexities of these loops are turned
+down stream. These basins for the most part open out in southerly or
+westerly directions which makes it improbable that ice-bearing bodies
+of water occupied them. But if this were not fatal, certainly the
+fact that the convexities of the boulder belts are turned down stream
+and cross the centers of the basins is precisely contrary to the
+distribution they must have assumed if they were due to floating ice
+in bodies of water occupying the basins. I hold it, therefore, to be
+beyond rational question that these tracts were deposited as we find
+them by the margins of the glacial lobes that invaded the region.
+
+If these boulder belts were of the same nature as the average boulders
+of the till-sheets beneath them, then the simple fact of unusual
+aggregation might be plausibly referred to the accidents of gathering
+and deposition. But they are very clearly distinguished from the
+average boulders of the till by several characteristics.
+
+1. They are superficial. Sometimes they rest completely on the surface,
+sometimes they are very slightly imbedded, sometimes half buried,
+sometimes they protrude but a slight portion, and sometimes they are
+entirely concealed, but lie immediately at the surface. In all cases
+the aggregation is distinctly superficial. Where they are buried, the
+burying material is usually of different texture and composition from
+the subjacent till, and appears to be distinct in origin from it. The
+superficiality of the tract is very obvious almost everywhere, and is
+especially so in regions where the subjacent till is of the pebble-clay
+rather than boulder-clay order, for the comparative absence of boulders
+below emphasizes the contrast. Throughout most of the region the
+subjacent till is not of a very bouldery type, so that the distinction
+is generally a marked one.
+
+2. The boulders of the belts are almost without exception derivatives
+from the crystalline terranes of Canada. Those of the great tract
+especially under consideration were derived from the typical Huronian
+rocks of the region north of Lake Huron, and from granitic and
+gneissoid rocks referable to the Laurentian series of the same region.
+These last, however, cannot be sharply distinguished from the granitic
+rocks derived from other parts of the Laurentian terrane. The Huronian
+rocks are very easily identified because of the peculiarities of some
+of the species. Among these the one most conspicuously characterized
+is a quartz-and-jasper conglomerate. The matrix is usually a whitish
+quartzite. This is studded with pebbles of typical red jasper and of
+duller rocks of jasperoid nature, which grade thence into typical
+quartzite pebbles. With these are mingled crystalline pebbles of other
+varieties. Another peculiar erratic comes from the "slate conglomerate"
+of Logan. It consists of a slaty matrix through which are scattered
+rather distantly pebbles of granitic, quartzitic and other crystalline
+rocks. This is one of the forms of the "basal conglomerate" of Irving.
+Other varieties of this "basal conglomerate" are present. In addition
+to these very peculiar rocks, a quartzite of a very light greenish
+semi-translucent hue has a wide distribution along the tract. It is
+readily distinguishable from the numerous other quartzites of the drift
+of the interior. Some years since, on returning from my first field
+examination of a portion of this belt, I sent a typical series of chips
+from the characteristic erratics to Professor Irving, who had recently
+returned from the study of the original Huronian region. He returned a
+suite of chippings that matched them perfectly throughout, all of which
+were taken _in situ_ in the region north of Lake Huron.
+
+Among the boulders of the belt are occasionally found specimens of
+impure limestone or of limy sandstone that might perhaps be referred
+doubtfully to some member of the paleozoic series; but on the other
+hand, might with equal or greater probability perhaps be referred to
+the similar rocks of the Huronian series. These are quite rare, never
+forming, so far as my observations go, as much as one per cent. of
+the series. In the several definite enumerations made to determine
+the percentage of the doubtful specimens, the result never exceeded
+a fraction of one per cent. In the most extensive enumeration the
+result was about one-half of one per cent. Aside from these doubtful
+specimens there are practically no boulders in the belts that can be
+referred to any of the paleozoic rocks that intervene in the 500 miles
+between the parent series north of Lake Huron and the tract over which
+the boulders are now strewn. Occasionally there may be seen erratics
+from the paleozoic series at or near the surface, but they are not
+usually so disposed on the surface as to appear to be true members of
+the superficial boulder tract. There is, therefore, the amplest ground
+for the assertion that these boulder tracts are of distant derivation,
+and that they are essentially uncommingled with derivatives from the
+intermediate region.
+
+3. The boulders of this series are much more angular than those of
+the typical till sheets. Some of them, indeed, are rounded, but the
+rounding is generally of the type which boulders derived by surface
+degradation and exfoliation present. They rarely have the forms that
+are distinctively glacial. Quite a large percentage are notably
+angular, and have neither suffered glacial rounding nor spherical
+exfoliation. Some few are glacially worn and scratched, but the
+percentage of these is small.
+
+The tracts therefore present these four salient characteristics: (1)
+the boulders are derived from distant crystalline terranes (400 to 500
+miles) and are essentially uncommingled with rock from the intervening
+paleozoic terranes; (2) they are essentially superficial, and the
+associated earthy material has a texture differing from that of the
+subglacial tills; (3) they are notably angular and free from glacial
+abrasion, except in minor degree; (4) the tracts are so associated with
+terminal moraines and so related to the topography of the region, that
+there is no rational ground for doubt that the boulders were borne to
+their present places by the glaciers that produced the correlative
+moraines.
+
+In contrast to these superficial boulder formations, the till sheets
+below are made up of a very large percentage of glacial clay whose
+constitution shows that it was produced in part by the grinding down
+of the paleozoic series. In this are imbedded boulders and pebbles
+that were derived from the paleozoic series as indicated by their
+petrological character, and, in many instances, demonstrated by
+contained fossils. While a small part of the boulders contained in the
+till are angular or but slightly worn, the larger part are blunted,
+bruised, scratched and polished by typical glacial action. This obvious
+grinding of the boulders, taken in connection with the clay product
+resulting from the grinding, affords a clear demonstration that the
+deposit was produced at the base of the ice by its pushing, dragging,
+rolling action.
+
+The two formations, therefore, stand in sharp contrast; the one
+indicating the passive transporting action of the ice in bearing from
+their distant homes north of the lakes the crystalline boulders and
+dropping them quietly on the surface, the other indicating the active
+dynamic function of the ice in rubbing, bruising and scoring the
+material at its base. The one seems to me a clear instance of englacial
+and superglacial transportation; the other an equally clear example of
+subglacial push, drag and kneading.
+
+Now if it were the habit of an ice-sheet of this kind to carry material
+from its bottom to the surface by internal movement, it would seem
+that the distance of 400 to 500 miles which intervened between the
+source of the crystallines and the place of their deposit would have
+furnished ample opportunity for its exercise, and that there would
+have been commingled with the englacial and superglacial material many
+derivatives from the intermediate region, and these derivatives should
+have borne the characteristic markings received by them while at the
+base of the ice. The very conspicuous absence of such commingling,
+and the absence or phenomenal rarity of anything that even looks like
+such a commingling, appears to me to testify in quite unmistakable
+terms to the distinctness of the methods of transportation. In view
+of the great territory over which this particular belt is spread,
+and the greater territory which is embraced in the other tracts not
+here specially considered, there is left little ground for doubt
+that this distinctness of englacial from basal transportation was
+a prevailing fact and not an exceptional one. This is supported
+by concurrent evidence derived from the territory west of Lake
+Michigan. This territory unfortunately does not bear erratics that
+have equally distinct characteristics, but, so far as my observation
+goes, the phenomena are alike throughout. I am therefore brought to
+the conclusion that, in the interior at least, there was no habitual
+lifting of boulders from the base of the ice sheets to the surface,
+nor any habitual commingling of basal with englacial and superglacial
+material, except, of course, as it took place by virtue of the falling
+of the latter through crevasses to the base, and by mechanical
+intermixture of the two at the edge of the ice.
+
+The amount of englacial till under this view is little more than that
+which was lodged in the body of the ice in its passage over the knobs
+and ridges of the hilly and semi-mountainous regions of the north. To
+this is perhaps to be added occasional derivatives from the more abrupt
+prominences of the paleozoic region and the superficial dust blown upon
+the ice from the surrounding land, which was probably the chief source
+of the silty material intermingled with the superficial boulders. The
+total amount is thus quite small, though important in its significance.
+
+The eskers and kames of the region are made up of derivatives from
+the basal material as shown by (1) the local origin of the material
+in large part, (2) the mechanical origin of the sands and silts, (3)
+the not infrequent glacial markings of the pebbles and boulders, and
+(4) the disturbed stratification of the beds.[12] If I am correct
+in respect to the kind and amount of the englacial and superglacial
+material, it is obvious that eskers and kames, such as are found in the
+interior, could not be derived from englacial or superglacial sources.
+The term englacial as here used does not include such materials as
+may be lodged in the basal stratum of the ice and brought down to the
+actual bottom by basal melting.
+
+[12] See "Hillocks of Angular Gravel and Disturbed Stratification," Am.
+Jour. Sci. Vol. XXVII., May 1884, pp. 378-390.
+
+The conclusions drawn from the phenomena of the plains of the interior
+are not necessarily applicable to more hilly or mountainous regions.
+
+                                                    =T. C. Chamberlin.=
+
+
+
+
+=_Studies for Students._=
+
+
+DISTINCT GLACIAL EPOCHS, AND THE CRITERIA FOR THEIR RECOGNITION.[13]
+
+[13] Read before the American Geological Society at Ottawa, Dec., 1892.
+
+
+I. =Introduction.=
+
+It has long been evident that writers on glacial geology are not at
+one concerning some of the important questions which underlie the
+interpretation of the history of the glacial period. Certain recent
+publications have served to emphasize the differences between them.
+There are two questions, at least, concerning which there must be
+agreement, or at any rate a common understanding, before existing
+differences can be eliminated or justly evaluated. When the answers
+to these questions have been agreed upon, or when the positions of
+the contending parties are clearly understood, it may be found that
+some of the apparent antagonisms have no better basis than differences
+in definition. Stated interrogatively, the two questions referred to
+are these: 1. What constitutes a glacial epoch as distinct from other
+glacial epochs? and 2. What are the criteria for the recognition of
+distinct glacial epochs, if such there were?
+
+
+II. =The Idea of a Glacial Epoch.=
+
+It is conceivable that, after the development and extension of a
+continental ice-sheet, it might be wholly wasted away. The maximum
+extension of such an ice-sheet would mark the culmination of a glacial
+epoch. If subsequently another ice-sheet of considerable dimensions
+were accumulated, its development and extension would constitute a
+second glacial epoch. These successive ice-sheets might be so related
+to each other in time, in position, and in the sequence of geological
+events, as to be regarded as separate epochs of the same glacial
+period.[14] On the other hand they might be so widely separated from
+each other in time, in position, and in the sequence of geological
+events, as to make their reference to separate glacial periods more
+appropriate. In any case their separation would be sufficiently marked
+to necessitate their reference to separate ice epochs. So far we
+believe there would be no disagreement.
+
+[14] The terms period and epoch are here used in the sense in which
+they have been used most commonly in the literature of glacial geology
+in the United States.
+
+If, instead of entirely disappearing, the first ice-sheet suffered
+great reduction of volume and area, and if this reduction were followed
+by a second great expansion of the ice, might the time of such
+expansion be regarded as a second glacial epoch of the common glacial
+period? To this question, too, as thus stated, we apprehend there would
+be but one answer, and that affirmative.
+
+It seems certain that the edge of the continental ice-sheet was subject
+to more or less extensive oscillations, as are the ends of glaciers
+and the edges of ice-sheets to-day. How much of an oscillation is
+necessary, and under what attendant conditions must it take place, in
+order that the recession of the ice-edge shall mark an interglacial and
+its re-advance a distinct glacial epoch? When the question takes this
+specific form, and when inquiry is made concerning the quantitative
+value of the different elements entering into the problem, we reach
+the battled ground. It is the battled ground, partly because it is
+the ground of misunderstanding. It is the ground of misunderstanding,
+partly because glacialists are not agreed as to the meaning of certain
+terms in common use by them.
+
+Four elements seem to enter into the idea of an ice epoch as distinct
+from other ice epochs. These are (1) the distance to which the ice
+retreated between successive advances; (2) the duration of the retreat,
+or the time which elapsed between successive ice extensions; (3) the
+temperature of the region freed from ice during the time between maxima
+of advance; and (4) the intervention between successive advances, of
+changes interrupting the continuity of geological processes.
+
+(1.) It would be arbitrary to name any definite distance to which
+the ice must recede in order to constitute its re-advance a distinct
+ice epoch. It would be not so much a question of miles as a question
+of proportions. Considering this point alone, we presume it would
+be agreed that an ice-sheet should have suffered the loss of a very
+considerable proportion of its mass, and that it should have dwindled
+to proportions very much less than those subsequently attained, before
+its re-advance could properly be called a separate glacial epoch. To be
+specific, if the North American ice-sheet, after its maximum extension,
+retreated so far as to free the whole of the United States from ice,
+we should be inclined to regard a re-advance as marking a distinct
+ice epoch of the same glacial period, if in such re-advance the ice
+reached an extension comparable with that of the earlier ice-sheet.
+Especially should we be inclined to refer the second ice advance to a
+second glacial epoch, if it, as well as the preceding retreat, were
+accompanied by favoring phases of some or all the other three elements
+entering into the notion of a glacial epoch. In this statement we
+do not overlook the fact that a northerly region--as Labrador or
+Greenland--might be continuously covered with ice throughout the time
+of the two glaciations of the more southerly regions. But this is not
+regarded as a sufficient reason for discarding the notion of duality.
+Greenland has very likely been experiencing continuous glaciation since
+a time antedating that of our first glacial deposits. The renewal
+to-day of glaciation comparable in extent to that of the glacial period
+would certainly be regarded as a distinct glacial epoch, if not a
+distinct glacial period, even though Greenland's glaciation may not
+have been interrupted. Scandinavia and Switzerland have probably not
+been freed from ice since the glacial period. Their snow and ice fields
+are probably the direct descendants of the ice fields of the glacial
+period. An expansion of the existing bodies of ice in these countries
+to their former dimensions, would constitute a new glacial epoch, if
+not a new glacial period. Analogous subdivisions in pre-Pleistocene
+formations have been frequently recognized.
+
+(2) The application of the time element is hardly susceptible of
+quantitative statement. We are inclined to think that it would be
+generally agreed that, with a given amount of recession of the ice, its
+re-advance would be more properly regarded as a distinct glacial epoch
+if the interval which had elapsed since the first advance were long.
+Whether a longer time between the separate advances might reduce the
+amount of recession necessary in order to constitute the second advance
+a second epoch, we are not prepared to assert; but we are inclined to
+think it might.
+
+(3) The third element is perhaps somewhat more tangible than the
+second. If, during the retreat of the ice, the climate of a region
+which was twice glaciated became as temperate as that of the present
+day in the same locality, we should be inclined to regard the preceding
+and succeeding glaciations as distinct ice epochs, especially if the
+intervening recession were great and its duration long.
+
+Unfortunately for simplicity and ease of determination, there are
+difficulties in determining with precision how far the ice retreated
+between successive maxima of advance, how long the interval during
+which it remained in retreat, and the extent to which the climate was
+ameliorated, as compared with that which went before and that which
+followed.
+
+(4) If changes of any sort which interrupt the continuity of geological
+processes intervened between successive maxima of advance of the ice,
+the separation of the later advance from the earlier, as a distinct
+ice epoch, would be favored. How great the intervening changes should
+be in order to constitute the re-advance a distinct ice epoch, is a
+point concerning which there might be difference of opinion. But it is
+altogether possible that such changes might intervene as alone to give
+sufficient basis for the separation. Orographic movements, resulting
+either in continental changes of altitude or attitude are among the
+events which might come in to separate one ice epoch from another.
+Changes of this sort have often furnished the basis for the major
+and minor divisions of time in other parts of geological history, so
+that there can be no question as to their adequacy, if they were of
+sufficient magnitude. We hold that the intervention of orographic or
+other important geologic changes might reduce to a minimum the amount
+of recession, the duration of the recession, and the warmth of the
+intervening climate necessary to constitute the separate ice advances
+separate ice epochs. The absence of great orographic or other changes
+in glaciated regions between successive advances of the ice would be
+no proof that such advances should not be regarded as separate epochs.
+Divisions of equal importance have often been made without evidence of
+such changes.
+
+From the foregoing discussion, brief as it is, it will be seen that
+within certain narrow limits the definition of a glacial epoch, as
+distinct from other glacial epochs, must be more or less arbitrary.
+It is less important that an arbitrary definition should be accepted,
+than that the same meaning should be attached to technical terms in
+common use among geologists. In the interest of harmony and of a common
+understanding, and without the violation of any truth of science, we
+believe it would be well if the conception of a glacial epoch, as
+framed by those who are our leaders in position and in fact, were made
+the basis for our usage of the term.
+
+
+III. =The Criteria of Distinct Glacial Epochs.=
+
+If there have been differences of opinion concerning the nature of ice
+epochs, as distinct from each other and from ice periods, there has
+been a failure to adequately apprehend the nature, the extent, and the
+meaning of the real criteria on which the final recognition of separate
+ice epochs, if such there were, must be based.
+
+Such criteria are several in number. They are of unequal value. In some
+instances a single one of them might be quite sufficient to establish
+the fact of two ice epochs. In other cases, single criteria which might
+not be in themselves demonstrative, have great corroborative weight,
+when found in association with others. In all cases, much discretion
+must be used in the interpretation of these criteria. They may be
+enumerated under several specific heads.
+
+(1) _Forest Beds._ Beds of vegetal deposits or old soils are frequently
+found between layers of glacial drift. This is one of the criteria
+most commonly cited, because it is of common occurrence and easy of
+recognition. The advocates of the unity of the glacial period maintain
+that such beds of organic matter might become interbedded with morainic
+debris during minor oscillations of the ice's edge. The phenomena of
+existing glaciers make it evident that forest beds or soils might
+be enclosed by the deposits of an oscillating ice edge. By repeated
+oscillations of the ice's edge during the general retreat of the ice,
+such vegetal beds might become interstratified with glacial drift more
+or less frequently over all the area once covered by the ice, and from
+which it has now disappeared. The mere presence of vegetable material
+between beds of drift is therefore no proof of distinct ice epochs.
+This does not destroy the value of the vegetal beds as a criterion for
+the recognition of distinct ice epochs, but it makes caution necessary
+in its application. It does not follow that, since _some_ inter-drift
+forest-beds do not prove interglacial epochs, _none_ do. The question
+is not how forest-beds might originate, but how existing forest-beds
+did originate.
+
+Where the plant-remains found in the relations indicated are so well
+preserved as to make identification of the species possible, we have
+a means of determining, with some degree of accuracy, the climatic
+conditions which must have obtained at the place where the plants grew
+during the time of their life. If these interbedded plant-remains are
+of such a character as to indicate a temperate climate, we can not
+suppose that they grew at the immediate edge of the ice, and therefore
+that they were buried beneath its oscillating margin. To be specific,
+if the inter-drift plant remains in any given locality of the area
+once covered by ice are such as to indicate a climate _as warm as the
+present in the same locality_, the ice must have receded so far to the
+northward that its re-advance might, in our judgment, appropriately be
+regarded as a separate ice epoch.
+
+It has been suggested in opposition that temperate conditions may
+obtain even up to the edge of the ice, and that interbedded vegetal
+remains indicating temperate climate do not prove any considerable
+recession of the ice. The phenomena about existing glaciers have been
+appealed to in support of this demurrer. But the objection is not well
+taken. The climatic conditions which obtain about the borders of small,
+local glaciers, are not a safe guide as to climatic conditions which
+obtained about the margin of a continental ice-sheet, any more than the
+climatic conditions which obtain about a small inland lake are a safe
+criterion as to the climatic conditions about a sea-coast. The general
+principles of climatology, as well as specific facts concerning plant
+distribution, seem to us to indicate that the climate about the border
+of a continental ice-sheet must have been arctic.
+
+It is evident that the greater the distance north of the overlying
+drift remains of temperate plants are found, the more conclusive
+becomes the evidence. Plant remains indicating temperate climate at
+the very margin of the drift sheet which overlies them, would be less
+conclusive than similar evidences one hundred miles to the northward.
+It might be difficult to prove in any given instance that the ice which
+deposited the drift overlying plant remains advanced one hundred miles,
+or any other specific distance, south of any particular underlying
+forest bed. If the forest bed were continuous for the whole distance,
+the case would be clear. It would also be conclusive if the continuity
+of the drift overlying a forest bed at any point with that of a
+remote point to the south, could be demonstrated. In spite of these
+difficulties in its application, the vegetal beds constitute a valuable
+criterion in making the discriminations under consideration, when they
+are properly applied. Under proper circumstances the criterion may be
+conclusive when taken alone, and it may have corroborative significance
+when not itself conclusive.
+
+The absence of forest beds and of all traces of vegetal deposits
+whatsoever between beds of drift, is no proof of the absence of
+recurrent ice epochs, since the second advance of the ice might have
+destroyed all trace of the preëxistent soil and its vegetal life. It
+is always possible, too, that such beds exist, even if they have not
+been discovered. It would have been anticipated that they would not be
+abundant, or wide spread. The absence of forest beds is therefore at
+best no more than negative evidence.
+
+(2) _Remains of Land Animals._ Bones of mammalia or remains of other
+land animals, occurring in relations similar to those in which forest
+beds occur, may have a like significance. Their value as a criterion of
+separate glacial epochs is subject to essentially the same limitations
+as forest beds.
+
+(3) _Inorganic Products formed during a time of Ice Recession._
+The recession of the ice after a maximum of advance would leave
+a land surface more or less affected with marshes and ponds. In
+such situations, bog iron ore might accumulate, if conditions were
+favorable. Such ore beds, buried by the drift of a later ice advance,
+would have a significance comparable to that of forest beds, except
+that they would give less definite information as to climate, and would
+be correspondingly less trustworthy. Should such ore beds be found in
+such relations as to prove that the underlying and overlying bodies
+of drift were deposited by ice sheets which extended great distances
+further south, their significance would be enhanced. From the thickness
+of the ore beds some inference might be drawn as to the length of time
+concerned in their accumulation. But because of the variable rate
+at which bog ore may accumulate, such inference should be used with
+caution.
+
+Concretions of iron oxide might be formed in the marshes or in
+ill-drained drift areas where accumulations of greater extent were
+not made. A subsequent incursion of the ice might incorporate these
+nodules with its drift, wearing and striating them as other stones,
+and depositing them as constituent parts of the later drift. Such
+iron nodules in the later drift would mean a recession and re-advance
+of the ice with some considerable interval between, although not
+necessarily an interval sufficiently warm or long to be regarded as
+an interglacial epoch.[15] Calcareous concretions, like those of the
+loess, would possess a like significance, in like relations. While in
+themselves these inorganic products of a time of ice recession might
+fail to be conclusive of separate ice epochs, they might have much
+corroborative significance when associated with other phenomena. An
+inter-till iron ore bed, associated with a forest bed which indicated a
+warm climate, would be most significant.
+
+[15] This point concerning iron nodules was suggested to the writer by
+Mr. W. J. McGee.
+
+The absence of knowledge of ore beds between sheets of till, and the
+absence from an upper bed of till of concretions of iron and lime
+carbonate formed during a recession of the ice, would be no proof that
+interglacial epochs did not occur. These products were probably formed
+in relatively few localities. They stood good chance of destruction at
+the hands of the returning ice, and they may exist, where they have not
+been discovered, or where their significance has not been understood.
+Their absence is at best no more than negative evidence.
+
+(4) _Beds of Marine and Lacustrine Origin._ If between beds of glacial
+drift there be found beds of lacustrine or of marine origin, such beds
+would indicate a recession of the ice during their time of deposition.
+Their position would be a minimum measure of ice recession. If such
+lacustrine beds contain organic remains, they will bear testimony
+concerning the climatic conditions which existed where they occur,
+at the time of their deposition. If the fossils in such beds denote
+a temperate climate, or a climate as mild as that of the present day
+in the same region, the ice must have receded so far to the northward
+as, in our judgment, to constitute its re-advance a distinct ice
+epoch. This line of argument may be even stronger than that drawn
+from remains of terrestrial life, since the ice would probably affect
+the temperature of the sea to greater distances than that of the
+land, and affect it to a greater degree within a given distance. The
+argument becomes stronger the further north the inter-drift marine and
+lacustrine deposits occur, since the ice must always have receded to
+a position still further north. If marine or lacustrine beds lying far
+north of the later ice limit contain proof of temperate climate, the
+argument becomes conclusive.
+
+The absence of marine and lacustrine deposits between beds of drift,
+would be no proof that interglacial epochs did not occur. Lacustrine
+beds could be made only where there were lakes, and lakes would be the
+exception rather than the rule. Marine beds in similar positions would
+rarely be known, except where a definite succession of changes of level
+has taken place. Both classes of deposits, if once formed, would be
+subject to destruction by the over-riding ice of a later epoch, if such
+there were. Neither would be likely to be preserved at all points where
+formed, and both may exist at many points where their existence is
+not known. The absence of these beds is at best no more than negative
+evidence.
+
+(5) _Beds of Subaërial Gravel, Sand and Silt._ Layers of stratified
+drift between layers of ground moraine are of common occurrence in many
+regions. Under ordinary conditions their existence is not regarded as
+evidence that the underlying and overlying tills are to be referred
+to separate ice epochs. But it is conceivable that beds of stratified
+drift may, under the proper circumstances and relations, be strong
+evidence of separate ice epochs. The last stages of ice work in the
+glacial period were accompanied, in many regions, by the deposition
+upon adjacent land surfaces, of extensive bodies of gravel and sand,
+washed on beyond the ice by waters issuing from it. Except in valleys
+through which strong currents coursed, such deposits were apparently
+not carried far beyond the edge of the ice. But as the edge of the ice
+withdrew to the northward, sand plains may have extended themselves
+in the same direction, by additions to their ice-ward faces. It is
+conceivable that the process of subaërial plain building at the edge
+of a receding phase of ice, might be carried so far under favorable
+circumstances, as to result in the construction of plains of great
+extent. In this event, a subsequent ice-advance might overspread
+such plains in such wise as to bury, without destroying them, though
+such a course of events would certainly be exceptional. In order to
+constitute the interstratified gravel and sand evidence of separate
+ice-epochs, its continuity for great distances between beds of till,
+and in the direction of ice movement, would need to be demonstrated.
+In themselves, these beds, under the conditions indicated, would
+simply be a minimum measure of the amount of ice recession between
+the deposition of the underlying and overlying bodies of till. It is
+hardly likely, though possible, that the continuity of interbedded
+gravel and sand could be proved for a sufficient distance north of the
+southern limit of the less extensive bed of ground moraine, to alone
+constitute evidence of a recession of ice great enough to make it
+necessary to refer its re-advance to a new epoch. Beds of silt in like
+relations, deposited by waters beyond the edge of the ice, would have
+a like significance so far as the question here under consideration
+is concerned. Such beds of stratified drift might sometimes have
+corroborative value when their testimony, taken by itself, is
+inconclusive. If, for example, their surfaces are marked by forest
+beds, and especially by forest beds whose plants denote a warm climate,
+the association becomes most significant.
+
+In view of what has been said, it is evident that the absence of beds
+of subaërially stratified silt, sand, and gravel, between beds of till
+can not be brought in evidence against separate ice epochs. It would
+rarely be true that topographic and hydro-*graphic conditions would
+make possible the construction of plains of sufficient extent to serve
+as criteria for the purpose here indicated, and few of those formed
+would escape such a degree of destruction as to leave them demonstrably
+continuous. There is also the further possibility that such beds exist,
+even though their continuity be not known. To prove the continuity of
+a buried bed of stratified and incoherent drift, even if it existed,
+would be a most difficult task.
+
+(6) _Differential Weathering._ If, after covering a given region, the
+ice retreated, the drift which it left in the area which it previously
+covered would be subject to oxidation, leaching and disintegration.
+The depth to which this oxidation, leaching and disintegration would
+extend, would be dependent upon the length of time during which the
+drift was exposed, and upon the climate which affected the region
+during its exposure. The longer the exposure and the warmer the
+climate, the deeper would the weathering extend. If, subsequently,
+the ice extended over the same region, it might, in some places,
+override and bury the old surface without destroying it. The earlier
+oxidized and leached drift would thus come to be buried by the newer,
+unoxidized, unleached drift. If, therefore, beneath the newer drift
+of any given locality there be found a lower drift, the surface of
+which is oxidized and leached to a considerable depth, the evidence
+is strong that the lower drift was exposed for a long period of time
+before the upper drift was deposited upon it. Within certain limits a
+similar result might be brought about, it is true, if the ice, after
+having reached a certain maximum stage of advance, were to retreat for
+a short distance only and there remain for a very long period of time.
+A subsequent minor advance might bury the oxidized surface of the drift
+beyond the position of the long ice-halt. Under these conditions, the
+climate which would have obtained in the area of the drift exposed
+during the minor retreat would have been cold, and oxidation, leaching,
+and disintegration would have proceeded slowly. If they reached
+considerable depths, the time involved must have been very long. If
+this surface of oxidized and leached and disintegrated drift were found
+to reach far to the northward beneath the layer of newer and upper
+drift, it would indicate a great recession of the ice. We maintain that
+if it were found sufficiently far north of the margin of the overlying
+drift, and if its depth were sufficiently great, extending well down
+below any possible accumulation of superglacial till, it might be a
+positive criterion of so great a recession of the ice, protracted
+through so great an interval of time, as to constitute its new advance
+a separate ice epoch.
+
+There is much reason to believe that the soil developed under the
+influence of a warm climate differs in some respects from one developed
+from similar material under other conditions. The well-known fact that
+red and reddish soils are especially characteristic of low latitudes
+and warm climates is significant. If therefore a soil developed on
+the surface of one sheet of drift and buried by another, be found
+to possess, in addition to unmistakable marks of long exposure, the
+peculiar marks which seem to be characteristic of soils developed under
+high temperatures, the argument gains in strength.
+
+This argument from oxidation and weathering has another application.
+If in a later advance, following a protracted recession, the ice-sheet
+failed to reach the limit of its earlier advance, there would remain
+an area of drift deposited by the first ice-sheet, outside the drift
+deposited by the later. Now if the time interval between these two
+advances was great, and especially if during this interval the climate
+was mild, the oxidation and weathering of the older drift surface would
+be markedly different in degree from that of the newer. If, under
+these circumstances, the surface of the older sheet were found to be
+weathered and oxidized and reddened up to the border of the newer
+drift sheet, and if here there were found to be a sudden change in
+the character of the surface of the drift so far as depth and degree
+of oxidization and weathering is concerned, we should have strong
+evidence that the one sheet of drift was much older than the other.
+The statement sometimes urged that the drift which was deposited near
+the edge of the greatest ice advance would be largely made up of the
+residual materials which occupied the surface invaded by the ice,
+would not meet the case. For if it be granted that this statement is
+qualitatively good, we should find the greatest degree of weathering
+and oxidation at the extreme margin of the drift, and it should be
+found to be less and less on receding from this margin. There would in
+this case be no sudden transition from a deeply weathered and oxidized
+surface, to one which is fresh and unoxidized, along a definite line.
+We maintain that if the whole of the drift deposits are referable to
+one epoch, there should be no sudden transition in the surface of the
+drift from that which is deeply weathered to that which is not, the
+one surface being separated from the other by a definite and readily
+traceable line.
+
+It has been urged against the criterion of differential weathering
+that superglacial material is or may be thoroughly oxidized before
+its deposition, and that a layer of oxidized drift between layers of
+till may be no more than superglacial debris deposited during a minor
+recession of the ice.[16] We believe that this attempt to eliminate
+the value of this criterion rests partly on an exaggerated idea
+concerning the amount of superglacial material, but more especially
+on a failure to apprehend the real meaning of the argument for the
+validity of the criterion, and upon a failure to note the limitations
+imposed upon it by its advocates. It is not affirmed that a layer of
+oxidized drift between beds of unoxidized drift is _per se_ proof of
+two glacial epochs; but it is affirmed that if such layer of weathered
+drift can be shown to extend far below any possible superglacial till,
+into the subglacial till below, in such wise as to indicate that it
+is the result of subaërial exposure in a warm climate subsequent to
+its deposition and prior to the deposition of the overlying till,
+it constitutes the best possible evidence of an interglacial epoch,
+especially when accompanied by the corroborative testimony of other
+criteria. It is further affirmed that if the second sheet of drift
+failed to reach the limit of the first, and if the drift which was
+deposited by the first and never covered by the second ice-sheet, is
+more thoroughly and more deeply weathered than that deposited by the
+second, and especially if the two types of drift surface meet along
+a definite and readily traceable line, the argument becomes, in our
+judgment, irrefragable. In its application, this criterion would be
+infallible only in the hands of one who could distinguish between
+superglacial and superglacially oxidized material on the one hand, and
+material subaërially weathered after its deposition, on the other.
+
+[16] This point was urged at the reading of the paper at Ottawa, by
+Prof. C. H. Hitchcock, Mr. Upham, and others.
+
+In circumstances and relations where the weathering of the drift is
+not in itself conclusive, it might still have corroborative value in
+association with other lines of evidence.
+
+The absence of an oxidized and disintegrated zone of drift below a
+superficial layer which is not oxidized, would be no proof that there
+were not distinct ice epochs, since the ice of any later epoch, if such
+there were, might have planed off the surface of the drift left by its
+predecessor to the depth of the weathering. The preservation of such
+surfaces after a second ice invasion must be regarded as the exception
+rather than as the rule. There is always the possibility, too, that
+an oxidized and weathered zone marking the surface of an older drift
+sheet exists, where excavations have not opened full sections of drift
+to view. The absence of weathered zones of drift beneath the surface,
+or the absence of knowledge of their existence, is therefore at best
+no more than negative evidence. The absence of greater weathering of
+the drift outside the limit of the drift supposed to belong to a later
+epoch, would be positive evidence against the reference of the two
+sheets of drift concerned to different epochs.
+
+A specific part of the above line of evidence may be separately
+mentioned. One phase of weathering is the disintegration of boulders,
+and this is a point which can be readily applied even by those who are
+not geologists. If the boulders of one region are much more commonly
+disintegrated than those of another, and if the two regions are
+separated from each other by a well-marked boundary line, the inference
+lies close at hand that the boulders in the one case have been much
+longer exposed to disintegrating agencies than in the other. It is
+no answer to this argument to say that the materials lying at the
+very front of the drift deposits contain boulders which were derived
+from the disintegrated rock over which the ice has passed, and that
+they were therefore in a less firm state at the outset. In many cases
+these boulders have come from great distances, and coming from great
+distances they must have come in a firm and solid state, else they
+could not have suffered such extensive transportation, except indeed
+their position was superglacial throughout their whole journey. This
+argument has equal force when applied to the area covered by the two
+sheets of drift where two exist. If within the region of drift under
+investigation we find a surface layer of greater or less depth,
+the boulders of which are hard and fresh, and if beneath this we
+find another layer of drift, the stony material of which is largely
+disintegrated, at least in its upper parts, we have good evidence
+that the surface bearing the disintegrated boulders was exposed for
+a considerable length of time before the deposition of the overlying
+drift, which carries fresh boulders. Since the disintegration of
+boulders is only one phase of weathering, the limitations of this
+argument are identical with those already noted in connection with the
+general argument from differential weathering.
+
+(7) _Differential Subaërial Erosion._ If the drift deposited by one
+ice-sheet were to be exposed for a considerable interval of time, and
+if the ice in its subsequent advance failed to reach the limit of
+its first invasion, the two areas should show different amounts of
+subaërial erosion, since the one has been exposed to the action of air
+and water much longer than the other. The line which marks the limit
+of the later ice invasion should be the line of more or less sudden
+transition from an area without, where stream erosion has been greater,
+to an area within, where stream erosion has been less.
+
+The point here made can not be met by the suggestion that the greater
+erosion of the outer area was effected by the water issuing from the
+ice which had retreated to the position now marked by the border of the
+area of the lesser erosion. So far as we know, such waters would be
+depositing, not eroding. Furthermore, much of the erosion of the outer
+area would have such relation to drainage lines that waters issuing
+from the ice could never have reached the localities where it is shown.
+
+If the outer and older drift be found to have suffered ten times as
+much stream erosion as the inner and newer, it is fair to assume that
+it has been exposed something like ten times as long, if the conditions
+for erosion are equally favorable in the two regions. The argument has
+especial weight if it can be found that beneath the newer drift the
+surface of the older is such as to indicate that it was deeply eroded
+before the newer was placed upon it. The argument is stronger the
+farther from the margin of the newer drift such erosion on the surface
+of the underlying older drift can be proved to have taken place. In
+other words, if, in addition to the greater surface erosion of the
+older drift sheet as now exposed outside the limit of the newer drift,
+we find a notable unconformity between the newer and the older drift,
+and especially if this unconformity lie far enough north of the margin
+of the newer drift, the argument becomes conclusive.
+
+When differential erosion and drift unconformities are not in
+themselves conclusive, they may have great corroborative value in
+conjunction with differential weathering, forest beds, or other
+indications of separate ice epochs.
+
+The absence of observable unconformity between sheets of drift would
+be no proof that there were not distinct and widely separated ice
+epochs, since the later ice invasion might have so far modified the
+surface which it transgressed, as to destroy all patent evidences
+of unconformity. It would have been anticipated that distinct
+unconformities in the drift would be rare, even if there were distinct
+ice epochs, for the same reason that weathered zones and forest beds
+would be rare. But if the drift which lies outside a line supposed to
+mark the limit of a sheet of drift belonging to a later ice epoch, be
+not more eroded than that which lies within such line, the absence of
+greater erosion in the outer drift is positive evidence against the
+reference of the drift of the two areas to distinct ice epochs, if
+conditions for erosion in the two areas are equally favorable.
+
+(8) _Valleys Excavated Between Successive Depositions of Drift._ A
+closely related, but not identical, point may be found in the extent of
+the valley excavations which can be proved to have taken place between
+the deposition of the earlier and later drift. We do not refer to
+valleys excavated in the drift especially, but to those excavated in
+other formations as well. If it can be shown, for example, that after
+the deposition of an earlier drift sheet, and before the deposition
+of a later, valleys were excavated which extended not merely into the
+drift itself, but far beneath the drift into the underlying rock,
+these valleys would be conclusive evidence of a long interval between
+the deposition of the two bodies of drift. The argument is of especial
+force when such excavations in the rock beneath the drift can be shown
+to have taken place at great distances within the margin of the newer
+drift. For valleys in such situations imply that the ice had receded at
+least as far to the north as they lie, during the interval between the
+two drift depositions, and may be so situated as to show that the ice
+had wholly left the drainage basin where they occur.
+
+The absence of evidences of deep valley excavations in any given region
+during a supposed interglacial epoch, is no proof that such interval
+did not exist. The conditions may not have been everywhere favorable
+for erosion within the limits of any narrowly circumscribed area, and
+the absence of interglacial valleys would be only negative evidence
+against an interglacial epoch. The absence of such evidence everywhere
+would bear against the existence of an interglacial epoch of much
+duration in such wise as to be more than negative evidence.
+
+(9) _Different Directions of Movement._ If, after its maximum advance,
+the ice suffered merely a minor recession and then remained stationary,
+or nearly so, for a time, the general direction of its movement in a
+subsequent advance would probably be essentially the same as in the
+earlier. But if, after its maximum advance, the ice receded to a great
+distance, and especially if it entirely disappeared, a subsequent
+ice-sheet might have a very different direction of movement, since
+its center of accumulation and dispersion might be very different.
+It is conceivable that this center might shift during the history of
+a single ice-sheet. In this case there should be a gradual change in
+the direction of ice movement, not an abrupt one. If, therefore, there
+be found one sheet of drift made by an ice movement in one direction,
+overlaid by another sheet of drift deposited by ice moving in a very
+different direction, with an abrupt transition between them, such
+drift sheets would be presumptive evidence of distinct ice epochs. An
+exception would need to be made in the case of drift sheets along the
+margins of confluent or proximate ice lobes. In such cases, if the
+one lobe temporarily secured the advantage of the other, drift beds
+formed by movements from opposite directions might be found in vertical
+succession, without being evidence of separate ice epochs.
+
+It is no part of the purpose of this essay to point out the
+difficulties which might arise in the application of this criterion
+of diverse directions of ice movements. It is possible that gradual
+changes in the direction of movement might leave records which would
+seem to indicate abrupt changes instead. This possibility makes care
+necessary in the application of the criterion, but does not destroy its
+value. When not itself conclusive, this criterion may be so associated
+with differential weathering, differential erosion, forest beds, etc.,
+that their combined testimony makes but one conclusion possible.
+
+The absence of evidence of radically diverse directions of movement
+during the time of deposition of the various sheets of drift, would
+be no proof that there were not distinct epochs. In the first place,
+the movements of different epochs might be harmonious--a condition of
+things more probable than any other if the more common views of the
+causes of glaciation be correct. In the second place, if the movements
+were diverse, the deposits might still be so similar that their
+differentiation, when the one is buried, might not be easily made. In
+the third place, the later ice might have so far incorporated the older
+drift material with that which belonged more properly to it, as to have
+destroyed all definition between them.
+
+(10) _The Superposition of Beds of Till of Different Physical
+Constitution._ After the retreat of an ice-sheet, the surface of the
+country thus discovered would be largely mantled with drift. This drift
+would serve to protect the underlying rock from disintegration. But
+where there was little or no drift, the rock surface would be subject
+to all the disrupting agencies which affect surface rocks. The same
+would be true of all rock surfaces bared by subaërial erosion after the
+disappearance of the ice. Under these conditions, if a second sheet
+of ice invaded the region in question after it had been long exposed,
+it would find a surface prepared to yield large bowlders. The result
+would be the deposition of a new sheet of drift containing bowlders
+much larger than those which would have been proper to an ice-sheet
+overspreading a surface but recently abandoned. If, therefore, in
+the upper of two layers of subglacial till, bowlders of great size
+predominate, as compared with those of a lower homologous layer, they
+may be indicative of a great interval of time between the deposition
+of the upper and lower beds of drift. If the home of these bowlders
+be far north of the limit of the lesser sheet of drift, the distance,
+as well as the duration, of the ice retreat must have been great, and
+the reference of the two beds of till to distinct ice epochs would be
+favored. The case might be so strong as to make no other interpretation
+possible. Where in itself inconclusive, this criterion would have
+corroborative significance. In its application, the discrimination of
+subglacial and superglacial till would be imperative.
+
+The absence of physical dissimilarity between superposed layers of
+subglacial till would not be proof of the absence of separate glacial
+epochs. The phenomena constituting the criterion could hardly be
+expected to be of common occurrence. They would never be obtrusive, and
+may easily have escaped attention where they exist.[17]
+
+[17] The 10th criterion, in the order here named, was suggested by Mr.
+McGee in the discussion which followed the reading of the paper at
+Ottawa.
+
+(11) _Varying Altitudes and Attitudes of the Land._ Another line of
+argument has to do with the altitude and attitude of the land during
+the deposition of various members of the drift complex. If during
+the deposition of one part of the drift that part of the continent
+covered by the outer part of the ice was low, the drainage from it
+would be sluggish. If the deposits of this drainage persist to the
+present time, we may find in their character evidence of the nature
+of the drainage, and therefore of the attitude of the land. If at a
+later time of drift deposition the glacial drainage in the same region
+was more vigorous, the deposits made by the glacial streams would be
+correspondingly coarser. In these deposits, if they persist to the
+present day, we should find conclusive evidence of the swiftness of the
+streams. If it can be shown that during the deposition of one sheet of
+drift drainage was sluggish, and that during the deposition of a later
+body of drift the drainage was vigorous, these facts are evidence of an
+interval between the two times of drift deposition, sufficiently long
+to accomplish the corresponding changes in elevation or attitude. Since
+such changes of altitude and attitude are generally believed to have
+been accomplished slowly, the interval must be believed to have been of
+considerable duration.
+
+It is true that continental altitudes and attitudes might change during
+a single epoch of glaciation. If the change thus brought about resulted
+in increased slope, the more sluggish drainage of the earlier part
+of the epoch would be gradually transformed into the more vigorous
+drainage of the later part. In this case, if the evidence of both the
+earlier sluggish drainage and of the later vigorous drainage remain,
+there should also remain the evidence of the intermediate stages. If
+the deposits representing the intermediate condition of drainage do not
+exist, while those representing both extremes do, there would be the
+best of reason for believing that the intermediate phases of drainage
+did not exist during a glacial epoch, but during an interglacial
+epoch, when streams were not handling glacial debris, and when they
+were eroding rather than depositing. The deposits of the slow and of
+the swift drainage might occur in such relations as to prove, beyond
+peradventure, that intermediate stages of _glacial_ drainage never
+existed.
+
+If the sluggish drainage accompanied the maximum ice invasion, while
+the vigorous accompanied a lesser, the evidence of the swift streams
+might be found far north of the southern limit of the earlier drift.
+The farther north of the outer border of the older drift the gravel
+representing the vigorous drainage of the later and minor ice-sheet
+occurs, the further the ice must have retreated before the change from
+the one type of drainage to the other was effected. On the other
+hand, the farther north of the limit of the later ice advance the
+sluggish drainage accompanying the earlier ice-sheet may be traced,
+the farther must the ice have receded before the changes resulting in
+vigorous drainage occurred. Under certain relations, the retreat of the
+ice might be shown to have been great enough, before the orographic
+movements which altered the nature of the drainage, to constitute
+in our judgment, a re-advance a distinct ice epoch. If for example
+throughout the course of a long river whose basin was largely covered
+with ice, there be evidence that sluggish drainage obtained during the
+maximum ice advance, and during all stages of the ice retreat until the
+basin was free from ice, and if there be evidence of a vigorous glacial
+drainage in the same valley at a later time, with no gradations between
+the two types, we have proof positive of at least a great recession,
+and of a considerable elevation of the land after the ice had receded
+beyond the limits of the drainage basin and before it again reached
+it in its re-advance. We hold that these phases of glacial drainage
+deposits may be so related to each other, to the valleys in which
+they occur, and to more or less distinct bodies of glacier drift, as
+to prove so great a recession of ice between the diverse phases of
+drainage deposition, as to constitute the second advance a distinct ice
+epoch.
+
+The absence of evidence that the land stood at different elevations
+during different parts of the period of drift deposition, does not
+in any way militate against the theory of recurrent and distinct ice
+epochs. A constant attitude of the land is the thing to be assumed,
+until positive evidence to the contrary is adduced.
+
+(12) _Vigor and Sluggishness of Ice Action._ If it can be shown that
+during one epoch of glaciation, we will say the epoch of maximum ice
+extension, the ice action was relatively sluggish, while during a later
+and minor advance its action was vigorous, the difference of action
+might be regarded as presumptive evidence of distinct ice epochs.
+Evidence of the two phases of ice action here referred to are difficult
+of definition, but they have been independently noted by more than
+one glacialist. It is true that a forward oscillation of the ice edge
+might be more forceful than an earlier forward movement which might
+have reached a greater extension. In itself, therefore, this line of
+evidence can not be regarded as possessing great value.
+
+It has been indicated that under certain circumstances, and in certain
+relations, some of the foregoing criteria, taken singly, may be
+conclusive of glaciations so distinct from each other, as to make their
+reference to separate epochs proper. But where the facts and relations
+which constitute one of the criteria are found, the facts and relations
+constituting one or more of the others are likely to be found as
+well. Where two of the foregoing criteria are found to be coexistent,
+their joint force is greater than that of either one. If neither one
+be absolutely conclusive, the two may still be, since the one may
+exactly meet the deficiency of the other. If three or more concurrent
+lines of evidence exist in any locality, the case is still further
+strengthened. We maintain that several of the foregoing criteria may be
+so related to each other and to the formations concerned, as not only
+to make the recognition of separate ice epochs proper, but to make the
+failure of such recognition altogether unscientific. Even when a single
+line of evidence, or when double, or triple, or quadruple lines of
+evidence are not absolutely conclusive in ruling out every conceivable
+technical escape from the conclusion that there were separate ice
+epochs, their cumulative and corroborative force may still be such as
+to carry conviction scarcely less positive than that which mathematical
+demonstration would afford. In the nature of the case not all of these
+various lines of evidence could be expected to be found in any one
+locality, or perhaps in any one limited geographic area, but where one
+occurs, some or all of the others are liable to be found under favoring
+circumstance. The number of criteria, and the great extent of area
+where they may hope for application, afford great possibilities.
+
+From the foregoing discussion, it will be readily seen that the nature
+of the criteria and the limitations imposed upon their application by
+the difficulty of proving stratigraphic continuity in such a formation
+as the drift, necessitate the greatest care in their use, and reduce
+the value of hasty and inexpert conclusions to a minimum.
+
+
+IV. =Areas Where the Criteria find Readiest Application.=
+
+The foregoing criteria find their readiest application in regions where
+a later sheet of drift, suspected of belonging to a later ice epoch,
+failed to reach the border of an earlier sheet of drift, suspected of
+belonging to an earlier ice epoch. The 1st, 2d, 3d, 4th, 5th and 10th
+as enumerated above, find their application wholly within the area
+affected by the drift of the separate epochs, if such there were. While
+within this general area they may be looked for at any point, they
+are likely to be of rare occurrence, except along a somewhat narrow
+belt, say 50 to 100 miles, adjacent to the border of the lesser ice
+advance. The conditions for their occurrence and detection are greatly
+favored if the lesser drift sheet be the later. The 6th, 7th, 9th and
+12th criteria might hope for application within the same belt, but
+especially along a narrow zone on either side of the margin of the
+later drift sheet. It is along this zone that the types of surface are
+thrown into sharpest contrast, both as to material and topography. The
+8th and 11th criteria have still wider limits of application, both
+within and without the border of the lesser ice advance.
+
+                                                 =Rollin D. Salisbury.=
+
+
+
+
+                            =_Editorials._=
+
+
+It is the chief function of the national, state and provincial
+geological surveys to bring forth the great concrete facts relative
+to the structure and resources of their several fields. Within their
+special domains they also do an important work in the correlation
+of structures and formations, in the systematic aggregation of the
+facts, in the organizing of results, and in the development of the
+fundamental principles of geological science. To some extent they are
+permitted to do this beyond their own fields, but in the main the
+boundaries of these fields are the limits of their coördinations. They
+therefore leave a great function to be performed by some other agency
+in the coördination of interstate, international, and intercontinental
+factors. They are also restrained by their relationships to a somewhat
+too narrowly utilitarian public from devoting much direct attention
+to the solution of the deeper and broader problems that constitute
+the soul of science, though their contributions bear upon these in
+the most radical and important way. In the primary work of systematic
+observation, and the development of the immediate conclusions that
+spring therefrom, these surveys surpass all other agencies in the
+value of their contributions to the growth of the science, but in
+the secondary and ulterior work of correlation, in the synthetic
+aggregation and organization of results, and in the analytical and
+philosophical treatment of the whole, they need to be supplemented
+by agencies whose facilities and limitations lie in other lines,
+agencies whose relations and dependencies are complementary in nature.
+This secondary and ulterior work, in some degree, has been done by
+individual master students of systematic and philosophical geology, but
+to a very great extent it has not been done at all. It is a function
+which properly falls to universities, if the universities can only rise
+to meet it; for it is the function of universities, in the larger
+modern view, not only to rehearse science, nor merely even to educate
+young geologists, important as that is, but to develop science for
+science's own sake, and for its own inherent and permanent utilities
+as distinguished from its immediate applicabilities. To fulfill this
+function they must not only realize and appreciate it, but they must
+be equipped for field and experimental work, as well as library and
+laboratory study. Ideal correlations and academic systematizing are as
+apt to be hindrances as helps to the progress of science. While a few
+of the great universities of this country and Europe have made notable
+advances in these directions, the universities are, on the whole, far
+behind the great surveys in the performance of the work which properly
+falls to them. This is due not so much to a lack of appreciation of the
+function as to the lack of facilities.
+
+With the development of this higher function of the universities there
+goes a coördinate function for a university journal of geology, a
+journal whose special efforts shall be devoted to promoting the growth
+of systematic, philosophical, and fundamental geology, and to the
+education of professional geologists. No part of the wide domain can
+wisely be neglected by any journal, but there seems to be an open field
+for a periodical which specially invites the discussion of systematic
+and fundamental themes, and of international and intercontinental
+relations, and which in particular seeks to promote the study of
+geographic and continental evolution, orographic movements, volcanic
+coördinations and consanguinities, biological developments and
+migrations, climatic changes, and similar questions of wide and
+fundamental interest. This field is not likely to be successfully
+cultivated except by a systematic endeavor, pursued through a period of
+years, to bring together the latest and best summations of the results
+attained in the several national fields in a common medium, where they
+can be compared and discussed, and where tentative correlations will
+suggest themselves, out of which, in turn, working hypotheses will
+naturally spring, leading on to such direct investigations as the
+nature of each question invites. It would be presumptuous to assume
+that the =Journal of Geology= can cultivate with more than very partial
+success this field, but it especially invites contributions of this
+class.
+
+Another phase of geology which is thought to stand in much need of
+active cultivation is found in the clear and sharp analysis of its
+processes, the exhaustive classification of its phenomena, especially
+on genetic bases, the development of criteria of discrimination, the
+more complete evolution and formulation of its principles and the
+development of its working methods. The recent opening of new fields
+of research and the rapid progress of several new and important
+departments of the science give peculiar emphasis to this need. The
+rising generation of geologists, the hope of the science, should be
+schooled in these latest and most critical aspects of the science. A
+department of the =Journal=, entitled "Studies for Students," has been
+opened for the special cultivation of this field and for its adaptation
+to advanced students and progressive teachers of geology. Mere
+elementary presentations of processes and principles are not desired,
+but searching and critical expositions are solicited suited to the
+needs of young geologists who seek the highest professional equipment,
+and to progressive teachers who desire the fullest practicable command
+of the newest developments of the subject. These contributions may not
+be without their value to those who have already borne a considerable
+part of the heat and burden of life's professional day.
+
+It is our desire to open the pages of the =Journal= as broadly as a
+due regard for merit will permit, and to free it as much as possible
+from local and institutional aspects. It will have the very important
+advantage of being published under the auspices and guarantee of the
+University of Chicago, and will be free from the usual financial
+embarrassments attending the publication of a scientific magazine. This
+necessarily imposes upon the local editors the immediate responsibility
+for its editorship. Beyond this, it is hoped that its institutional
+relationship will disappear entirely in an earnest effort to promote
+the widest interests of the science. As an earnest of this wider
+effort several eminent geologists, representing some of the leading
+universities of this country, and some of the great geological
+organizations of Europe, have kindly consented to act as associate
+editors.
+
+                                                               T. C. C.
+
+[Illustration]
+
+Upon invitation of the World's Congress Auxiliary of the World's
+Columbian Exposition committees were appointed by the several sections
+of the American Association for the Advancement of Science at its
+Rochester meeting to coöperate with it in completing the organization
+of scientific congresses to be held at Chicago in connection with the
+forthcoming World's Fair. The committee appointed by the geological
+and geographical section consisted of Thomas C. Chamberlin, John C.
+Branner, Grove K. Gilbert, W. J. McGee, Rollin D. Salisbury, Eugene A.
+Smith, Charles D. Walcott, J. F. Whiteaves, Geo. H. Williams, H. S.
+Williams and N. H. Winchell.
+
+It has been arranged that this committee should undertake the work
+of preparing the scientific program for the Geological Congress. The
+committee have prepared a provisional schedule of topics, which they
+have submitted to the Advisory Council for revision. It has seemed
+to the committee that all contributions should be such as to have an
+international interest. Preferably, they should be subjects that can
+only be treated most advantageously in such a congress, especially
+those that involve the bringing together of data from different lands
+for comparison. The committee suggest the organization of the subjects
+under the following general classes:
+
+=First.= Such as shall show the present state of geological progress.
+It is believed that this can best be done by an exhibition of
+geological maps which shall show the latest and best results of
+official and other surveys. As such maps will be prepared, it is hoped,
+for the World's Fair, duplicates can be made at a slight expense for
+the use of the Congress. It is hoped that each country that has made
+any notable progress in mapping its geological formations will furnish
+for the Congress at least a general geological map, if not also special
+or analytical maps.
+
+=Second.= Such subjects as bear upon continental growth and
+intercontinental relations. It is proposed to make this a leading
+line of discussion during the Congress, in the belief that there is
+no subject more appropriate, and that there is none which better
+represents the present efforts of geologists or commands a more
+general interest. It is hoped that analytical maps will be prepared
+by the geologists of the several countries representing the stages of
+growth of these regions in each of the great eras from the Archean
+to the Pleistocene, and that such analytical maps may constitute a
+leading feature of the several presentations. Among the subjects upon
+which contributions are specially invited are the following: The
+correlation of continental and intercontinental orographic movements
+and geographic accretions by sedimentation; The coördination of periods
+of vulcanism in the different countries; The coördination of climatic
+states and changes; The correlation of faunal and floral variations
+and migrations. It is hoped that one session may be devoted to such
+coördination papers bearing upon each of the great subdivisions: viz.,
+Archean, Paleozoic, Mesozoic, Cenozoic, and Pleistocene.
+
+=Third.= Papers on Paleontological and Archeological Geology of
+international scope.
+
+=Fourth.= Contributions to Physical, Structural and Petrological
+Geology having international or general bearings.
+
+=Fifth.= Contributions to Economic Geology having general bearings.
+
+=Sixth.= Miscellaneous papers of especial and general interest.
+
+The foregoing groups are intended to embrace and coördinate the list of
+special themes announced in the circular issued by the local committee
+some months since, except such as may be best suited to popular
+presentation, for which special provision is to be made.
+
+It will be determined later, when the number and nature of the papers
+are ascertained, whether all will be arranged so as to form a
+continuous program, or whether sub-sections will be formed and two or
+more sessions held simultaneously.
+
+It is the desire of the World's Congress Auxiliary that a few addresses
+of a popular nature shall be given, with a view to stimulating an
+interest in the development of the science on the part of the public.
+
+                                                               T. C. C.
+
+[Illustration]
+
+Extra copies of the articles appearing under the head of Studies for
+Students will be printed and kept on sale for the use of teachers and
+advanced classes. The prices will be fixed as low as practicable, and a
+standing list published in the advertising columns of the =Journal=.
+
+
+
+
+                             =_Reviews._=
+
+
+  _On the Glacial Succession in Europe._ By Prof. =James Geikie=.
+       Transactions of the Royal Society of Edinburgh, Vol. XXXVII.,
+       Part I. (No. 9), 1892, pp. 127-149 (with a map).
+
+In this timely essay Prof. Geikie reaches the following conclusions:
+
+1. The record of the first glacial epoch is found in the Weyborn Crag
+of Britain, and the ground moraine beneath the "Lower Diluvium" of the
+continent. During this epoch, the direction of the ice movement in
+southern Sweden was from the south-east to the northwest. This first
+glacial epoch of which direct evidence is adduced was followed by an
+interglacial interval, during which the forest-bed of Cromer, the
+breccia of Hötting, the lignites of Leffe and Pianico, and certain beds
+in central France were deposited. During this interglacial epoch, the
+climate is believed to have been very mild.
+
+2. There followed a second epoch of glaciation, when the ice sheet of
+Britain became confluent with that of the continent. This was the epoch
+during which the ice sheet reached its southernmost extension. Its
+depositions are found in the lower boulder clays of Britain, the lower
+diluvium of Scandinavia and north Germany (in part), the lower glacial
+deposits of south Germany and central Russia, the ground moraines and
+high level gravel terraces of Alpine lands, and the terminal moraines
+of the outer zone. During this second glacial epoch, Alpine glaciers
+are believed to have attained their greatest development. This epoch
+of extreme glaciation was followed by an interglacial interval, during
+which Britain is believed to have been joined to the continent. During
+this interval, the climate became temperate. In Russia (near Moscow)
+there seems to be evidence that it was milder and more humid than that
+of the same region at the present day. Toward the close of the mild
+epoch, submergence seems to have been accompanied by an increasing
+degree of cold, which finally ended in another glacial epoch.
+
+3. The subsidence which marked the close of the second interglacial
+interval, marked likewise the inauguration of the third glacial
+epoch. Its work is represented in Britain by the upper boulder clay,
+in Scandinavia and Germany by the lower diluvium (in part), in central
+Russia by the upper glacial series, in Alpine lands by ground moraines
+and gravel terraces. The ice sheets of Scandinavia and Britain were
+again confluent, but did not extend quite so far south as during the
+second glacial epoch. This third glacial epoch is believed to have
+been followed by another interglacial interval, during which fresh
+water alluvia, lignite and peat accumulations were made. These are
+represented by the interglacial beds of north Germany, and by some
+of the so-called post-glacial alluvia of Britain. There were also
+marine deposits on the coasts of Britain and on the borders of the
+Baltic. During this interglacial interval, Britain is believed to
+have been continental. The climate was temperate, but in the course
+of time became more severe. This increasing severity seems to have
+been accompanied by submergence, which amounted to something like 100
+ft. below the present sea-level on the coasts of Scotland. The Baltic
+provinces of Germany were also invaded by the waters of the North Sea.
+
+4. There followed a fourth period of glaciation, during which the major
+part of the Scottish Highland was covered by an ice sheet. Local ice
+sheets existed in the southern uplands of Scotland and in mountain
+districts in other parts of Britain, and the great valley glaciers
+sometimes coalesced on the low lands. Icebergs floated out at the
+mouths of some of the highland sea-lochs. In some places, terminal
+moraines were deposited upon marine beds which were then in process of
+formation. These beds are now 100 ft. above the sea level. At this time
+Scandinavia was covered by a great ice sheet, which yielded icebergs
+to the sea along the whole west coast of Norway. The ground moraines
+and terminal moraines of the mountain regions of Britain represent the
+deposits of this ice epoch. The upper diluvium of Scandinavia, Finland,
+and north Germany represent the work of the contemporaneous, but not
+confluent, ice sheet of the continent. In the Alps, terminal moraines
+in the large longitudinal valleys were made at the same time.
+
+This fourth glacial epoch was followed by a fourth interglacial
+interval, during which fresh water alluvial deposits were made, and
+also the "lower buried forest and peat" of Britain and northwestern
+Europe. At this time, Scotland seems to have stood 45 to 50 feet lower
+than now, and Carse clays and raised beaches represent the work of the
+sea. During this interglacial interval, Britain is believed to have
+become again continental, while the climate became so far ameliorated
+as to allow the growth of great forests. Subsequently the insulation
+of Britain was effected, and this was followed by a climate which was
+probably colder than the present.
+
+5. The severity of the climate which marked the close of the fourth
+interglacial interval was such as to bring about local glaciation in
+some of the mountain valleys of Britain. Here and there the glaciers
+projected their moraines so far down the mountains that they rest on
+what is now the 45 to 50 feet beach. In the Alps, this fifth epoch of
+glaciation is represented by the so-called post-glacial moraines in
+the upper valleys. This is believed to have been the last appearance
+of glaciers in Britain. The dissolution of these glaciers was again
+followed by an emergence of the island, and by more genial climatic
+conditions.
+
+In support of his conclusions, Prof. Geikie cites some striking facts
+which are not so widely known as they should be. For example, Swedish
+geologists have found evidences that there was an ice sheet antedating
+that which deposited the "lower diluvium," and that during this earlier
+glaciation the direction of ice movement in southern Sweden was from
+the south-east to the north-west. The ground moraine deposited by this
+ice sheet is overlain by the "lower diluvium" which was produced by
+an ice movement from the north north-east to the south south-west, or
+nearly at right angles to the first. Again, near Moscow, there exist
+interglacial beds whose plant remains indicate a climate milder and
+more humid than that of the present time. These interglacial beds, it
+will be observed, occur in the region of the "lower diluvium" quite
+beyond the margin of the ice which produced the "upper diluvium" of
+Germany and Scandinavia. During this interglacial interval, Prof.
+Geikie maintains that no part of Russia could have been covered with
+ice. If, then, within the limits of the area covered by the "lower
+diluvium," and not by the "upper," distinct beds of glacial drift
+are separated by such beds as those cited, there can be no question
+but that such separation marks two distinct glacial epochs. If there
+was an earlier glaciation when the movement of the ice in Sweden was
+at right angles to that during which the lower part of the "lower
+diluvium" was produced, this also would seem to be good evidence of
+three ice epochs prior to the "upper diluvium." The epoch of the "upper
+diluvium" would then constitute the fourth glacial epoch, and this is
+the interpretation of Prof. Geikie.
+
+Outside the area of the European continental ice sheet, facts are
+adduced in striking confirmation of the multiple ice epoch theory.
+These facts are found in Switzerland, where evidences of multiple
+glaciation have been recognized, and in the Pyrenees where evidences
+of three separate ice epochs have been found. In France, evidences
+of an interglacial interval have been found in the region of the Puy
+de Dôme of such duration as to allow the excavation of valleys to a
+depth of 900 feet. The length of time which would be required for such
+stupendous erosion must certainly be regarded as sufficient to allow
+the preceding and succeeding glaciations to be considered as belonging
+to two distinct epochs.
+
+Another point of great significance and interest which Prof. Geikie's
+essay brings out, is the correlation in Britain between epochs of
+glaciation and epochs of subsidence on the one hand, and between
+interglacial intervals and epochs of elevation on the other. If Prof.
+Geikie's interpretation be well founded, and so far as we are able to
+judge from the facts presented this is the case, his conclusions would
+seem to be fatal to the hypothesis that glacial climate was produced by
+northern elevation.
+
+The map which Prof. Geikie gives, showing the limit of ice advance
+during the fourth glacial epoch, seems to us open to criticism. On the
+ground of personal observation, the writer believes that the ice sheet
+of the glacial epoch here represented did not extend notably, if at
+all, beyond the Baltic Ridge.[18]
+
+[18] See _American Journal of Science_, May, 1887. In a recent letter,
+Prof. Geikie indicates that he is convinced, from subsequent personal
+observation, that his map is erroneous so far as the limit of the ice
+of this epoch is concerned. The mapping given was based on the opinion
+of others.
+
+Prof. Geikie is an advocate of Dr. Croll's astronomical theory of
+glacial climate, and thinks that even five is not the full number of
+glacial epochs belonging to the Pleistocene period. He believes there
+may have been a series of glacial epochs increasing in severity to a
+maximum represented by what is now designated as the second glacial
+epoch. This maximum was followed by a series of epochs of diminishing
+severity, represented by what he designates the third, fourth and fifth
+epochs. The essay is a timely contribution to glacial geology.
+
+                                                 =Rollin D. Salisbury.=
+
+
+
+
+          =_Analytical Abstracts of Current Literature._=[19]
+
+[19] Abstracts in this number are prepared by Henry B. Kummel, Chas. E.
+Peet, J. A. Bownocker.
+
+
+  _The Sub-Glacial Origin of Certain Eskers._ By =William Morris
+       Davis=, Harvard University. (Proceedings of the Boston Society
+       of Natural History, Vol. XXV., May 18, 1892).
+
+A critical discussion of the conditions under which it is conceived
+certain eskers and sand plateaus (plains) were formed. The Auburndale
+district, ten miles east of Boston, presents three classes of modified
+drift deposits;--sand plateaus, eskers, and kames. These deposits are
+well exposed.
+
+The sand plateaus have the characteristics of delta deposits of
+glacial streams,--even surfaces, well-bedded sands and gravels, the
+beds sloping outward from the "head" at an angle of 12° to 20°, and in
+close agreement with the slope of the plateau front, a lobate margin,
+deposits distinctly coarser at the head than near the front, and a
+series of nearly horizontal roughly cross-bedded gravels overlying the
+sloping beds.
+
+The eskers are essentially of the same material as that of the plateau,
+often so poorly stratified as to render differentiation of the beds
+difficult. The interstices between the pebbles are often unfilled,
+although there is abundance of fine material in adjoining layers.
+This "open work" is taken to indicate rapid deposition, and seems to
+preclude the supposition that the gravels have settled down from a
+superglacial position, or been traversed by currents of any volume.
+In several instances the eskers can be followed to direct union with
+sand plateaus. Towards its lower end the esker frequently "gives out
+branches" and "the adjacent lowland surface becomes more or less
+encumbered with sand mounds or kames," indicating a decayed margin of
+the ice.
+
+Prof. Davis' conclusions are:
+
+"1. The eskers and sand plateaus of Auburndale and Newtonville were
+formed by running water just inside and outside of the ice margin in
+the closing stage of the last glacial epoch.
+
+"2. The ice-sheet was a stagnant, decaying mass at the time of their
+formation, as is shown by the ragged outline of its margin.
+
+"3. Eskers and sand plateaus are genetically connected; the term,
+feeding-esker, is fully warranted by the relation of the two in
+position, structure, and composition.
+
+"4. The sand plateaus were made rapidly; this is proved by the absence
+of disordered beds at their heads, where space would have been opened
+by the backward melting of the ice had the forward growth of the
+plateau been slow. The eskers were also made rapidly, as is shown by
+their 'open-work gravels.'
+
+"5. The diversion of the feeding streams to other outlets left the
+plateaus and the eskers without further energetic action as the ice
+melted away from them.
+
+"6. The present form and structure of the eskers are more accordant
+with the supposition of a subglacial origin than of a superglacial
+origin; but it is not intended to imply that other eskers of more
+irregular form and different structure could not have been deposited in
+superglacial channels."
+
+                                                               H. B. K.
+
+                   *       *       *       *       *
+
+
+  _Studies in Structural Geology._ By =Bailey Willis=, U. S. Geol.
+       Surv. (Transactions of the American Institute of Mining
+       Engineers, June, 1892).
+
+The paper aims "to present some of the results of observation of the
+geologists of the Appalachian division during the past three years
+on the subject of structural geology in the Appalachian province."
+The structural features are all of one type but of different phases,
+comprised in four great districts. 1) the district of close folding,
+2) a district whose chief structural characteristic is cleavage, 3) a
+district of open folding, 4) a district of faulting and folding. The
+answer to the questions, Why did the strata bend in the district of
+open folding, and why did they break in the district of faulting, is
+that the thrust affected them according to their rigidity under their
+respective conditions of superincumbent load. "We know that load up
+to a certain point restrains fracture in material under thrust." In
+the district of open folding the Devonian limestone is the most rigid
+of the strata and "the one which would most effectively transmit the
+compressing thrust and would control the resulting structure." In the
+district of open folding this limestone was prevented from breaking
+and faulting by a load of superincumbent strata exerting a pressure of
+10,000 to 23,000 pounds per square inch, while in the faulted district
+a load of 5,000 to 10,000 pounds per square inch permitted the strata
+to break and fault.
+
+The answer to the question, Why did the compression affect this
+zone, is given. "It becomes apparent on study of sections that where
+compression raised a great arch there previously existed a bend from
+a nearly horizontal to a descending position in the principal stratum
+transmitting the thrust. Greater anticlines and synclines originated in
+upward and downward convexity of initial dips, due to unequal deposits
+of sediments which depress underlying strata in proportion to their
+weight. Such folds may be called original." The Pottsville, Mahanoy,
+Shamokin and Wyoming coal basins of Pennsylvania belong to this class.
+
+Experiments have recently been carried on in the office of the United
+States Geological Survey reproducing the different forms of folding.
+The experiments differed from other experiments in that 1) the
+materials used to simulate the stratified rocks varied in consistency
+from brittle to plastic, according to the depth at which deformation is
+supposed to take place; 2) the compression was exerted under a movable
+load representing the weight of superincumbent strata; 3) the strata
+rested on a yielding base to simulate the condition of support of any
+arc of the earth's crust. The following are the conclusions from the
+experiments:
+
+1. "When a thrust tangentially affects a stratified mass, it is
+transmitted in the direction of the strata, and by each stratum
+according to its inflexibility. At any bend the force is resolved into
+components, one radial, the other tangential to the dip beyond the
+bend; the radial component, if directed downward, tends to depress the
+stratum and displace its support.
+
+2. "A thrust so resolved can only raise an anticline or arch which is
+strong enough to sustain the load lifted by its development; such an
+arch may be called competent; and since strength is a function of the
+proportions of a structure, it follows that, for a given stratum, the
+size of a competent anticline will vary inversely as the load; or for a
+given load the size will vary as the thickness of the effective stratum.
+
+3. "The superincumbent load borne by a competent anticline is
+transferred to the supports of the arch at the points of inflection of
+the limbs.
+
+4. "When a competent arch is raised by thrust from one side, the load
+transferred may so depress the resulting syncline further from the
+force that an initial dip will be produced in otherwise undisturbed
+strata; this dip will rise to a bend from which a new anticline may be
+developed. This anticline is a result of the first, and may be called
+'subsequent' in distinction to original folds. Since subsequent folds
+are simply competent structures, their size will be determined by
+conditions of thickness and load, and for like conditions they should
+be equal; and they must, in consequence of conditions of development,
+be parallel to the original fold and to each other. An example of an
+original fold with its subsequent anticlines is the Nittany arch and
+the group of parallel anticlines which lie southeast of it, extending
+northeast from the Broad Top basin."
+
+                                                               C. E. P.
+
+                   *       *       *       *       *
+
+
+  _The Catskill Delta in the Post-Glacial Hudson Estuary._ By =William
+       Morris Davis=. (From the Proceedings of the Boston Society of
+       Natural History, Vol. XXV., 1891).
+
+The post-Tertiary trenches of the Hudson and its tributaries are in the
+main filled with clay beds, which, covered by a thin deposit of sand,
+rise in terraces 130, 150, or even 180 feet above tide-water. These
+clays are the result of a late glacial or post-glacial submergence of
+the valley, but their upper surface does not indicate the amount of
+their submergence, as they are bottom deposits. Delta deposits made by
+the tributary streams, where they entered the Hudson estuary, would
+indicate the amount of submergence.
+
+Such deposits are found on the Catskill a mile north of Cairo, and
+eroded remnants are traceable for three or four miles down stream.
+The surface is characterized by great numbers of water-worn stones
+up to fifteen or eighteen inches in diameter. The lobate margin,
+where present, is poorly defined. These deposits range from 290 feet
+(aneroid) above tide, up river, to 270 feet further down. One-tenth of
+a cubic mile of material seems to have been washed into the Catskill
+trench at the point of this delta between the time of the ice departure
+and the elevation of the land. Subsequent terracing has removed half
+that amount.
+
+The course of the Catskill at Leeds, where it crosses a ledge of hard
+Corniferous limestone is probably of post-glacial superimposed origin,
+but the preglacial valley cannot be definitely fixed.
+
+                                                               H. B. K.
+
+                   *       *       *       *       *
+
+
+  _Geological Survey of Alabama.--Bulletin 4._ By =C. Willard Hayes=.
+       (Report of the Geology of Northeastern Alabama and Adjacent
+       Portions of Georgia and Tennessee).
+
+This report covers an area of 5950 miles, two-thirds in Alabama.
+Topographically it falls into three divisions: 1) the Cumberland
+and other plateaus of the northwest; 2) in the center, anticlinal
+valleys--Browns and Wills, with the synclinal mountains--Sand and
+Lookout; 3) the monoclinal mountains, the "flatwoods" (Coosa shales)
+and the chert hills (Knox limestone) of the southeast. The drainage of
+the first is radial from the center of the plateau to the Tennessee;
+that of the second, once consequent upon the folded structure, is now
+adjusted to the strike of the soft beds.
+
+The formations are Cambrian, Silurian, Devonian and Carboniferous.
+Total thickness is from 13,000 to 18,000 feet in the east, but
+decreases westward. Hard sandstones of the Carboniferous form the
+cappings of the plateaus and synclinal mountains. In the anticlinal
+and monoclinal valleys the Silurian and Cambrian appear. The rocks
+pass from the nearly horizontal beds of the plateau region, by narrow
+unsymmetrical anticlines with steeper dip on the northwest side, and
+by broad shallow synclines, to the complicated folds of the southeast.
+The axes of these latter folds dip more or less abruptly northward and
+southward, causing the ridges to assume zigzag courses. Synclines are
+often crossed by anticlines.
+
+Thrust faults exist, some of great magnitude, and traceable for 200
+to 300 miles. By the "Rome thrust fault" the Cambrian shales have
+been shoved four to five miles over upon the Carboniferous shales.
+Most of the overthrust strata have been worn away, but tongues of
+Cambrian shale still remain to all appearances lying conformably upon
+the Carboniferous strata. Transverse thrust faults terminate Gaylor's
+ridge, Dirt Seller Mountain, and Lookout Mountain on the south.
+
+                                                               H. B. K.
+
+                   *       *       *       *       *
+
+
+  _The Correlation of Moraines with Raised Beaches of Lake Erie._
+       By =Frank Leverett=, U. S. Geol. Surv. (Wisconsin Academy of
+       Science. Vol. VIII., 1891).
+
+References have been made in Geological literature to the beaches of
+the eastern portion of the Lake Erie basin, but up to the time of
+Mr. Leverett's work none of the beaches had been completely traced.
+Mr. Gilbert had discovered that several of the raised beaches do not
+completely encircle Lake Erie, and supposed that their eastern termini
+represent the successive positions of the front of the continental
+glacier during its retreat northeastward across the Lake Erie basin.
+Mr. Leverett verifies this theory by demonstrating that certain
+moraines are the correlatives of the beaches. They are as follows:
+
+I. The Van Wert or upper beach and its correlative moraine, the
+Blanchard ridge. II. The Leipsic or second beach and its correlative
+moraines. III. The Belmore, or third beach and its correlative moraine.
+
+I. The Van Wert beach extends eastward from the former southwestward
+outlet of Lake Erie near Fort Wayne, Indiana, to Findlay, Ohio, where
+it joins the Blanchard moraine. Through Indiana and Ohio its altitude
+is quite uniformly 210 feet above Lake Erie.
+
+While the Van Wert beach was forming, the ice front was the
+northeastern shore of the lake as far east as Findlay, Ohio, its
+position being marked by the Blanchard moraine. East of Findlay, where
+the Van Wert beach joins it, the moraine is of the normal type. But
+west of Findlay, it presents peculiarities of topography and structure,
+resulting from the presence of lake water beneath the ice margin.
+The water was shallow and incapable of buoying up the ice-sheet,
+and producing icebergs. The motion of the water under the ice-sheet
+produced a variable structure. This is the only instance of a moraine
+demonstrably formed in lake water.
+
+II. The Leipsic, or second beach, was formed after the ice had
+retreated from its position marked by the Blanchard moraine. Its
+altitude is 195 to 200 feet above Lake Erie. It has its terminus near
+Cleveland, where it connects with the western end of a moraine.
+
+III. The Belmore beach and its correlative moraine. Between the Leipsic
+beach and the present shore of Lake Erie are several beaches. One of
+these, the Belmore beach, terminates near Cleveland, while the others
+extend into southwestern New York, and probably connect with moraines,
+though this connection has not been traced. The general altitude of
+the Belmore beach in Ohio is 160 to 170 feet above Lake Erie. Unlike
+the Van Wert and Leipsic beaches, it does not directly connect with a
+moraine at its eastern end, but a gap of ten miles intervenes. Terraces
+at Cleveland, Mr. Leverett thinks, make a connection between the
+eastern end of the beach and the western end of the moraine at Euclid,
+Ohio.
+
+                                                               C. E. P.
+
+                   *       *       *       *       *
+
+
+  _The Climate of Europe During the Glacial Epoch._ By =Clement Reid=.
+       (Natural Science. Vol. I, No. 6, 1892).
+
+_Temperature of the Sea._--The temperature of the English Channel was
+similar to that where the isotherm of 32° F. is now situated. The
+winter temperature can scarcely have been 20° colder than at present.
+The Mediterranean was perhaps 5° colder than now.
+
+_Temperature of the Land (air)._--It does not appear that the climate
+of the lowlands of southern Europe can have been 20° lower than the
+present mean; 10° or perhaps less appear to have been the refrigeration
+in the Mediterranean region. The temperature at the southern margin of
+the ice-sheet was about 20° colder than at present. The temperature
+increased rapidly towards the south. Recent observations seem to show
+that throughout central Europe there was a period of _dry_ cold,
+causing the country to resemble the arid regions of central Asia.
+
+                                                               J. A. B.
+
+                   *       *       *       *       *
+
+
+  _On the Glacial Period and the Earth-Movement Hypothesis._ By
+       =James Geikie=, Edinburgh, Scotland. (Read before the Victoria
+       Institute, London).
+
+Geologists generally admit that there have been at least two glacial
+epochs, separated by one well-marked interglacial period. The closing
+stage of the Pleistocene period was one of cold conditions in
+northwestern Europe, accompanied by land depressions. After this came a
+genial climate with a union of the British islands among themselves and
+also with the continent. This was followed by a cold, humid condition.
+
+Upham maintains that the whole of North America north of the Gulf of
+Mexico stood at least three thousand feet higher at the beginning of
+the glacial epoch than at present. Fiords were formed before glacial
+times and so can not be cited as evidence of high land during the
+glacial period. An elevation of land in the northern part of North
+America and Europe could not produce glaciation in their southern
+parts. The deflection of the Gulf Stream by the sinking of the Panama,
+Professor Geikie argues, could not produce the conditions which
+prevailed during the glacial epoch. The Earth-Movement hypothesis, he
+believes, accounts neither for the widespread phenomena of the ice-age,
+nor for the remarkable interglacial climates. Some maintain that the
+warm interglacial period was produced by the rise of the Panama land,
+the sinking of the lands to the north, and the turning of the Gulf
+Stream from the Pacific into the Atlantic. Why then, asks Professor
+Geikie, do we not have such a climate now?
+
+                                                               J. A. B.
+
+
+
+
+                         =_Acknowledgments._=
+
+
+The following papers have been donated to the library of the Geological
+Department of the University of Chicago, mainly by their authors:
+
+=Abbe, Cleveland.=
+
+  --On the Production of Rain. 8 pp. 1892.
+
+=Ami, Henry M.=, M.A., F.G.S.
+
+  --On Canadian Extinct Vertebrates. 4 pp.--Ottawa Naturalist.
+
+  --On the Geology of Quebec and Environs. 26 pp., 1 pl.--Bull. Geol.
+       Soc. Am., vol. 2, pp. 477-502.
+
+  --On the Geology of Quebec City, Canada. 4 pp.--Canadian Record Sci.,
+       April, 1891.
+
+  --Additional Notes on Ganiograptus Thureani, McCoy, from the Levis
+       Formation Canada. 2 pp.--Canad. Record Sci., Oct. 1889.
+
+  --Reviews of Reports and Papers on Canadian Geology and Paleontology.
+       8 pp.--Ottawa Naturalist, Oct.-Dec. 1892.
+
+  --Notes and Descriptions of some new or hitherto unrecorded species
+       of Fossils from the Cambro-Silurian (Ordovician) Rocks of the
+       Province of Quebec. 15 pp.--Canadian Record of Sci., April, 1892.
+
+  --Review of Catalogue of the Fossil Cephalopoda of the British
+       Museum, Part 8, Nautiloidea. By Arthur H. Foord, F.G.S. 3
+       pp.--Canadian Record of Sci., Sept. 1891.
+
+  --On the Sequence of Strata forming the Quebec Group of Logan and
+       Billings, with Remarks on the Fossil Remains found therein. 4
+       pp.--Ottawa Naturalist, June, 1892.
+
+=Andeæ, A. and A. Osann.=
+
+  --Beiträge zur Geologie des Blattes Heidelberg. 39 pp., III., 2
+       pl.--Aus den Mittheilungen der Grossh. Badischen Geologischen
+       Landesanstalt, II Bd. VII-XI.
+
+=Baltzer, A.=
+
+  --Beiträge zur Geognosie der Schweizer-Alpen über die Frage,
+       ob der Granit-Gneiss der nördlichen Gränzregion der
+       Finsteraarhorn-Centralmass eruptiv sei oder nicht, und über
+       damit zusammenhängende Probleme. 41 pp., 2 pl.--Neues Jahrbuch
+       für Mineralogie, 1878.
+
+  --Beiträge zur Geognosie der Schweizer-Alpen. Ueber die Marmorlager
+       am Nordrand des Finsteraarhorn-massivs. 20 pp., 2 pl.--Aus dem
+       Neuen Jahrbuch für Mineralogie, 1877.
+
+  --Ueber den Hautschild eines Rochen aus der marinen Molasse. 4 pp., 1
+       pl.--Aus den Mittheilungen der Naturforschenden Gesellschaft in
+       Bern.
+
+  --Ueber den natürlichen Verkohlungsprozess. 23 pp.--Aus der
+       Vierteljahrs-schrift der zürcherischen naturforschenden
+       Gesellschaft.
+
+  --Randerscheinungen der centralgranitischen Zone in Aarmassiv. 18
+       pp., 1 pl.--Aus dem Neuen Jahrbuch, 1885. II Band.
+
+  --Beiträge zur Geognosie der Schweizer-Alpen. Ein Beitrag zur
+       Kenntniss der Glarnerschlinge. 20 pp., 1 pl.--Aus dem Neuen
+       Jahrbuch für Mineralogie, Geol. und Pal. 1876.
+
+  --Geologische Skizze des Wetterhorns in Berner Oberland. 14 pp., 2
+       pl., Zeit. der Deut. geolog. Gesell, 1878.
+
+  --Geognostich-chemische Mittheilungen über die neuesten Eruptionen
+       auf Vulcano und die Producte derselben. 29 pp., 3 pl.--Zeit. d.
+       Deut. Geolog. Gesell, 1875.
+
+  --Ueber Bergstürze in den Alpen. 50 pp., 1 pl.--Aus dem Jahrbuch des
+       S.A.C. (X. Jahrgang) Zürich, 1875.
+
+=Baker, Frank C.=
+
+  --Notes on a Collection of Shells from the Mauritius; with a
+       consideration of the Genus Magilus of Montfort. 22 pp., 1
+       pl.--Proc. Rochest. Acad. Sci., Vol. 2, 1892.
+
+  --Catalogue and Synonomy of the Recent Species of the Family of
+       Muricidæ, First Paper. 20 pp.--Proc. Rochest. Acad. Sci., Vol.
+       I, 1891.
+
+  --Description of New Species of Muricidæ with Remarks on the Apices
+       of Certain Forms. 9 pp., 1 pl.--Proc. Rochest. Acad. Sci., Vol.
+       I, 1891.
+
+=Barrois, Charles.=
+
+  --Sur la présence de fossiles dans le terrain azoique. 4 pp.--Comptes
+       Rendus des Séances de L'Académie des Sciences, Aug. 8, 1892.
+
+=Beecher, C.E., Ph.D.=
+
+  --The Development of some Silurian Brachiopods. 8 pl., 96 pp.--N. Yr
+       State Mus., Vol. I, No. I, Oct. 1892.
+
+  --Brachiospongidæ, a Memoir on a Group of Silurian Sponges. 28 pp., 6
+       pl. Memoirs of the Peabody Mus., Vol. II, Part I, 1889.
+
+  --Insecta by Alpheus Hyatt and J. M. Arms.--Am. Jour. Sci., March,
+       1891.
+
+  --New Types of Carboniferous Cockroaches from the Carboniferous
+       Deposits of the United States; (2) New Carboniferous Myriapoda
+       from Ill.; (3) Illustrations of the Carboniferous Arachnida
+       of N. A., of the orders Anthracomarti and Pedipalpi; (4) The
+       Insects of the Triassic Beds at Fairplay, Col., Samuel H.
+       Scudder. 2 pp.--Am. Jour. Sci., Jan., 1891.
+
+  --Some Abnormal and Pathologic Forms of Fresh Water Shells from the
+       Vicinity of Albany, N. Y. 2 pp., 2 pl.--36th Rep. N. Y. State
+       Mus. of Nat. Hist.
+
+  --The Development of a Paleozoic Poriferous Coral. Symmetrical Cell
+       Development in the Favositidæ. 12 pp., 7 pl.--Trans. Conn. Acad.
+       Sci., Vol. 8, 1891.
+
+  --On Leptænisca, a New Genus of Brachiopod from the L. Helderberg
+       Group. N. A. Species of Strophalosia. 8 pp., 1 pl.--Am. Jour.
+       Sci., Sept., 1890.
+
+  --Ceratiocaridæ from the Chemung and Waverly Groups at Warren, Penn.
+       22 pp., 2 pl.--Rep. of Prop., PPP, 2d Geol. Surv. Penn., 1884.
+
+  --A Spiral Bivalve from the Waverly Group of Penn. 4 pp., 1
+       pl.--39th An. Rep. N. Y. State Mus., 1886.
+
+  --On the Lingual Dentition and Systematic Position of Pyrgula. 8 pp.,
+       1 pl. Jour. N. Y. Mic. Soc., Jan., 1890.
+
+  --On the Occurrence of U. Silurian Strata near Penobscot Bay, Maine.
+       6 pp., Ill.--Am. Jour. Sci., May, 1892.
+
+  --Koninckina and Related Genera. 9 pp., 1 pl.--Am. Jour. Sci., Sept.,
+       1890.
+
+  --Development of the Brachiopoda, Part I, Introduction. 14 pp., 1
+       pl.--Am. Jour. Sci., Apr., 1892.
+
+  --Development of the Brachiopoda. Part II, Classification of the
+       Stages of Growth and Decline. 22 pp., 1 pl.--Am. Jour. Sci.,
+       Aug., 1892.
+
+=Beachler, Chas. S.=
+
+  --Keokuk Group of the Miss. Valley. 8 pp.--Am. Geol., Aug., 1892. 3
+       copies.
+
+  --The Rocks at St. Paul, Indiana and Vicinity. 2 pp.--Am. Geol.,
+       Mch., 1891. 3 copies.
+
+=Bigelow, Frank H.=
+
+  --Notes on a new Method for the Discussion of Magnetic Observations.
+       40 pp., 2 pl.--Bull. Weather Bureau, 1892.
+
+=Boehm, Georg.=
+
+  --Ueber den Fussmuskeleindruck bei Pachyerisma. 2 pp.--Berichte der
+       Naturforschenden Gesellschaft in Freiburg i. B., 1892. VI. 3.
+
+  --Megalodon, Pachyerisma und Diceras. 24 pp. 9 wood cuts.--Aus den
+       Berichten der Naturforschenden Gesellschaft VI. 2. zu Freiburg
+       i. B., 1891.
+
+  --Lithiotis Problematica. 16 pp., 3 pl.--Naturforschenden Gesell. in
+       Freiburg, Band II. Heft 3.
+
+  --Ueber das Alter der Kalke des col dei Schiosi. 4 pp.--Der Deut.
+       Geolog. Gesell, 1887.
+
+  --Ein Beitrag zur Kenntniss der Kreide in den Venetianer Alpen. 16
+       pp., 4 pl. 3 cuts.--Aus den Berichten der Naturforschenden
+       Gesellschaft zu Freiburg i. B. Band VI. Heft 4.
+
+  --Die Bivalven der Schichten des Diceras Muensteri (Diceraskalk) von
+       Kelhein. 8 pp.--Zeit. Deut. Geol. Gesell. 1881.
+
+  --Ueber die Fauna der Schichten mit Durga im Departement der Sarthe.
+       12 pp., 1 pl. 2 wood cuts.--Zeit. der Deut. geol. Gesell. Bd.
+       XL., 1888.
+
+  --Die Facies der grauen Kalke von Venetien im Departement der Sarthe.
+       6 pp.--Aus der Zeit. der Deut. geol. Gesell, 1887.
+
+  --Südalpine Kreideablagerungen. 6 pp.--Aus der Zeit. d. Deut. geol.
+       Gesell, Bd., 33, 2 Heft.
+
+  --Ueber eine Anomalie im Kelche von Millericrinus mespiliformis. 5
+       pp., Ill. Zeit. der Deut. Geol. Gesell., Bd. 43, Heft 3.
+
+=Bowerman, A.=
+
+  --The Chinook Winds and other Climatic Conditions of the Northwest. 6
+       pp.--Hist. and Sci. Soc'y of Manitoba, Apr. 22, 1886.
+
+=Blanford, W. T.=, LL.D., F.R.S.
+
+  --On Additional Evidence of the Occurrence of Glacial Conditions
+       in the Paleozoic Era, and in the Geological Age of the Beds
+       Containing Plants of the Mesozoic Type in India and Australia.
+
+=Brigham, Albert P.=
+
+  --A Chapter in Glacial History with Illustrative Notes from Central
+       New York.--Trans. Oneida Hist. Society, 1889-91.
+
+  --The Geology of Oneida County. 18 pp.--Trans. Oneida Hist. Society,
+       1887-88.
+
+  --Rivers and the Evolution of Geographic Forms. 21 pp., Ill.--Am.
+       Geog. Soc'y, Mch., 1892.
+
+=Chamberlin, T. C.=
+
+  --Hillocks of Angular Gravel and Disturbed Stratification. 12 pp.,
+       Ill.--Am. Jour. Sci., May, 1884.
+
+=Carter, Prof.= O. C. S.
+
+  --Ores, Minerals and Geology of Montgomery County, Pennsylvania, with
+       map.--Hist. of Mont. Co.
+
+  --Artesian Wells in the Lowest Trias at Norristown. 7 pp.--Proc. Am.
+       Phil. Soc., May 1, 1891.
+
+=Carpenter, Commander A.=, R. N.
+
+  --Soundings Recently Taken off Barren Island Narcondam, Pl.--Records
+       Geol. Sur. Ind., Vol. XX, Part 1, 1887.
+
+=Clarke, F. W.=
+
+  --The Meteoric Collection in the U. S. Nat. Mus. A Catalogue of
+       Meteorites Represented. Nov. 1, 1886. 13 pp. Ill., 1 pl.
+
+  --Some Nickel Ores from Oregon, Ill. 7 pp.--Am. Jour. Sci., June,
+       1888.
+
+  --Tschemak's Theory of the Chlorite group and its Alternative. 10
+       pp.--Am. Jour. Sci., March, 1892.
+
+  --On Nephrite and Jadeite. 15 pp. 1 pl. Proc. U. S. Nat. Mus. XI,
+       1888.
+
+  --Studies in the Mica Group. 6 pp.--Am. Jour. Sci., Aug., 1889.
+
+  --A New occurrence of Gyrolite. 2 pp.--Am. Jour. Sci., Aug., 1887.
+
+  --Experiments upon the Constitution of the Natural Silicates. 25
+       pp.--Am. Jour. Sci., Oct., Nov., Dec., 1890.
+
+  --Mica. 6 pp.--Min. Resources of the U. S., 1883-4.
+
+  --Note on the Constitution of Ptilolite and Mordenite.--Am. Jour.
+       Sci., Aug., 1892.
+
+  --On Some Phosphides of Iridium and Platinum on Cadmium Iodide.
+       Some Sp. Gr. Determinations. Researches on the Tartrates of
+       Antimony.--Am. Chem. Jour. Vol. V., No. 4.
+
+  --The Fractional Analysis of Silicates. 7 pp.--Jour. Am. Chem. Soc.,
+       Vol. XII, No. 10.
+
+  --A Theory of the Mica Group. 10 pp.--Am. Jour. Sci., Nov. 1889.
+
+=Clarke F. W. (and J. S. Diller.)=
+
+  --Topaz from Stoneham, Maine. 7 pp.--Am. Jour. Sci., May, 1888.
+
+  --Turquois from New Mexico. 7 pp.--Am. Jour. Sci., Sept., 1886.
+
+=Clarke F. W. (and Charles Catlett.)=
+
+  --A Platiniferous Nickel Ore from Canada. 3 pp.--Am. Jour. Sci.,
+       May, 1889.
+
+=Clarke F. W. (and E. A. Schneider.)=
+
+  --On the Constitution of Certain Micas, Vermiculites and Chlorites.
+       10 pp.--Am. Jour. Sci., Sept., 1891.
+
+=Cohen, E.=
+
+  --Ueber einige eigenthümliche Melaphyr-Mandelsteine aus Süd-Afrika.
+       15 pp. Map, 1 pl.--Aus dem Neuen Jahrb. Min., 1875. Mandelsteine
+       Aus Den Maluti-Bergen, Süd-Africa, 1 p. Ibid., 1880, Bd. I.
+
+  --Ueber Laven von Hawaii und einigen anderen Inseln des Grossen
+       Oceans nebst einigen Bemerkungen ueber glasige Gesteine im
+       allgemeinen. 30 pp.--Aus dem Neuen Jahrb. Min. Geol. und Pal.
+       1880, Bd. II.
+
+  --Goldführende Conglomerate in Süd-Afrika. 3 pp.--Mit. des naturw.
+       Vereins für Neu-Vorpommern und Ruegen, 1887.
+
+  --Ueber die Trennung von Thonerde, Eisenoxyd und Titansäure. 2
+       pp.--Aus Neuem Jahrb. für Min. 1884.
+
+  --Chemische Untersuchung des Meteoreisens von S. Juliao de Moreira,
+       Portugal, sowie einiger anderen hexaëdrischen Eisen. 12 pp.--Aus
+       dem Neuen Jahrbuch für Mineralogie, 1889, Bd. I.
+
+  --Zusammenstellung petrographischer Untersuchungsmethoden nebst
+       Angabe der Literatur. 36 pp.--Aus den Mit. aus dem naturw.
+       Verein für Neu-Vorpommern und Ruegen in Greifswald.
+
+  --Ueber die Entstehung des Seifengoldes. 20 pp.--Mit. des naturw.
+       Vereins für Neu-Vorpommern und Ruegen, 1887.
+
+  --Geonostisch-petrographische Skizzen aus Süd-Afrika. 48 pp. 1
+       pl.--Aus dem Neuen Jahrbuch, Min. 1874.
+
+  --Ueber einige Vogesengesteine. 6 pp.--Aus dem Neuen Jahrb. Min.
+       Geol. und Pal., 1883, Bd. I.
+
+  --Andalusitführende Granite. 3 pp.--Aus dem Neuen Jahrb. Min. 1887,
+       Bd. II.
+
+  --Nekrolog von Jonas Gustaf Oscar Linnarsson. 2 pp.--Aus dem Neuen
+       Jahrb. Min. 1882. Bd. I.
+
+  --Versammlung des Oberrhein, geologischen Vereins zu Duerkheim,
+       bayr. Rheinpfalz, am 13, 14 und 15 April, 1882. Ueber einen
+       Aventurinquartz aus Ostindien.
+
+  --Berichtigung bezüglich des "Olivin-Diallag-Gesteins" von
+       Schriesheim im Odenwald. 2 pp.--Aus dem Neuen Jahrb. Min. 1885,
+       Bd. I.
+
+  --Ueber Pleochroitische Höfe in Biotit. 5 pp.--Aus den Neuen Jahrb.
+       Min. 1888, Bd. I.
+
+  --Kersantit von Laveline. 2 pp.--Aus den Neuen Jahrb. Min. 1879.
+
+  --Das Labradoritführende Gestein der Küste von Labrador. 3 pp.--Aus
+       den Neuen Jahrb. Min. 1885, Bd. I.
+
+  --Ueber eine verbesserte Methode der Isolirung von
+       Gesteinsgemengtheilen vermittelst Flussäure. 3 pp.--Mit. des
+       naturw. Vereines für Neu-Vorpommern und Ruegen, 1888.
+
+  --Die Gold production Transvaal in Jahre 1889.
+
+  --Ueber eine Pseudomorphose nach Markasit aus der Kreide von Arcona
+       auf Ruegen. 4 pp.--Aus den Sitzungsberichten des naturw. Vereins
+       für Neu-Vorpommern und Ruegen, 1886.
+
+  --Das Obere Weilerthal und das Zunächst Angrenzende Gebirge.
+       150 pp.--Abhandlungen zur Geologischen Speciakarte von
+       Elsass--Lothringen.
+
+  --Ueber den Granat der süd-afrikanischen Diamantfelder und ueber den
+       Chromgehalt der Pyrope. 4 pp.--Aus der Mit. des naturw. Vereins
+       für Neu-Vorpommern und Ruegen, 1888.
+
+  --Ueber Speckstein, Pseudophit und dichten Muscovit aus Süd-Afrika. 6
+       pp.--Aus dem Neuen Jahrb. Min. 1887, Bd. I.
+
+  --Titaneisen von den Diamantfeldern in Süd-Afrika. 2 pp.--Aus dem
+       Neuen Jahrb. Min. 1877.
+
+  --Ueber den Meteoriten von Zsadany, Temesvar Comitat, Banat. 10
+       pp.--Aus den Verhandlungen des Naturhist-Med. Vereins zu
+       Heidelberg. II Bd., 2 Heft.
+
+=Cohen E.= und =W. Deecke=.
+
+  --Ueber Geschiebe aus Neu-Vorpommern und Ruegen. 84 pp.--Aus den
+       Mitt. des naturwiss. Vereines für Neu-Vorpommern und Ruegen,
+       1881.
+
+  --Sind die Stoerungen in der Lagerung der Kreide an de Ostküste von
+       Jasmund (Ruegen) durch Faltungen zu erklären? 10 pp. 3 pl.--Aus
+       den Mit. des naturwiss. Vereins für Neu-Vorpommern und Ruegen,
+       1889.
+
+  --Ueber das Krystalline Grundgebirge der Inseln Bornholm.
+
+=Cohen E.= und =E. Weinschenk=.
+
+  --Meteoreisen-Studien. 32 pp.--Annalen des K. K. Naturhistorischen
+       Hofmuseums. Bd. VI. Heft 2, 1891.
+
+=Cross, Whitman.=
+
+  --The Post-Laramie Beds of Middle Park, Colo. 27 pp.--Proc. Colo.
+       Sci. Soc., Oct. 3, 1892.
+
+  --Post-Laramie Deposits of Colorado. 22 pp.--Am. Jour. Sci., July,
+       1892.
+
+  (and L. G. Eakins).
+
+  --A New Occurrence of Ptilolite.--Am. Jour. Sci., Aug., 1892.
+
+=Crosskey, H. W.=
+
+  --On a section of Glacial drift recently explored in Icknield Street,
+       Birmingham. 8 pp., 3 pl.--Proc. Birm. Phil. Soc. Vol. III, p.
+       209.
+
+  --Notes on some of the Glacial Phenomena of the Vosges Mountain, with
+       an account of the Glacier of Kertoff. 12 pp.--Jan. 9, 1879.
+
+  --Recent Researches into the Post-Tertiary Geology of Scotland. 12
+       pp.--Phil. Soc., Glasgow, Dec. 7, 1868.
+
+  --On the Tellino Calcarea Bed at Chappel Hall, near Airdrie.
+
+  --Some additions to the Fauna of the Bridlington (post-Tertiary) Bed.
+       6 pp.--Proc. Birmingham Phil. Soc. Vol. II, part II, June 9,
+       1891.
+
+  --Report of the Committee of the B. A. A. S. appointed for the
+       purpose of recording the position, height above sea-level,
+       character, etc. of Erratic blocks of Eng. Wales and Ire.--Brit.
+       Assoc. 1873, 1878, 1882, 1883, 1884, 1885, 1886, 1887, 1888,
+       1891.
+
+  (and =David Robertson=).
+
+  --The Post-tertiary Fossiliferous Beds of Scotland. 16 pp., 1
+       pl.--Trans. Geol. Soc. Glasgow, Vol. IV, Part III, page 241. 8
+       pp., Vol. V., Part I, page 29.
+
+=Davis W. M.=
+
+  --The Convex Profile of Bad Land Divides.--Sci., Oct. 28, 1892.
+
+  --The Deflective Effect of the Earth's Rotation. 8 pp.--Am. Met.
+       Jour., April, 1885.
+
+  --The Subglacial Origin of Certain Eskers. 23 pp.--Proc. Boston Soc'y
+       of Nat. Hist. Vol. XXI, May, 1892.
+
+  --Outline of a Course in Elementary Descriptive and Physical
+       Geography for Grades IV. and V. in the Cambridge Grammar School,
+       1892-3. 4 pp.
+
+  --Outline of Elementary Meteorology. A synopsis of course "Geology I"
+       at Harvard College, 1892-3.
+
+=Dawson, Geo.= M.D., D. Sc., F.G.S.
+
+  --Recent observations in the Glaciation of Br. Columbia and Adjacent
+       Regions. 4 pp., 1 pl.--Geol. Mag., Aug., 1888.
+
+=Dawson, Sir Wm. J.=
+
+  --The Geological History of Plants. 2 pp.--Botanical Gazette, Vol.
+       XIII., No. 6.
+
+=Deeche, W.=
+
+  --Der Monte Vulture in der Basilicata (Unteritalien) 78 pp. 1 Map., 1
+       pl.--Aus dem Neuen Jahrb. Min. Geol. und Pal. Beilageband VII.
+
+=Dewey, Frederic P.=
+
+  --A Preliminary Catalogue of the Systematic Collection in Economic
+       Geology and Metallurgy in the U. S. National Museum. 256
+       pp.--Bull. U. S. Nat. Mus. No. 42.
+
+  --Plan to Illustrate Resources of the U. S. and their Utilizations,
+       at the World's Industrial and Cotton Centennial Exposition
+       of 1884-85 at New Orleans. 8 pp. Proc. U. S. Nat. Mus. 1884,
+       Appendix.
+
+  --Photographing the Interior of a Coal Mine. 8 pp., 4 pl.--Am. Inst.
+       Min. Eng., July, 1887.
+
+  --Some Canadian Iron Ores. 12 pp.--Trans. Am. Inst. Min. Eng., Vol.
+       XII. 1884.
+
+  --Report of the Department of Metallurgy in the U. S. National
+       Museum. 4 pp.--Report to the Nat. Mus., 1888-89.
+
+  --The Department of Metallurgy and Economic Geology in the U. S. Nat.
+       Mus. 26 pp.--Am. Inst. Min. Eng., Sept., 1890.
+
+  --Hampe's Method of Determination Cu_{2}O in Metallic Copper. 6
+       pp.--Proc. U. S. Nat. Mus., 1888.
+
+  --Porosity of Specific Gravity of Coke. 16 pp.--Trans. Am. Inst. Min.
+       Eng., June, 1888.
+
+  --The Lewis and Bartlett Bag-Process of collecting Lead Fumes at the
+       Lone Elm Works, Joplin, Mo. 32 pp., Ill.--Am. Inst. Min. Eng.,
+       Feb., 1890.
+
+  --Note on the Nickel-Ore of Russell Springs, Logan Co., Kan.--Am.
+       Inst. Min. Eng.
+
+  --Note on the Falling Cliff Zinc Mine. 2 pp.--Am. Inst. Min. Eng.,
+       May, 1891.
+
+  --The Heroult Process of Smelting Aluminum Alloys. 8 pp.--Am. Inst.
+       Min. Engin., Feb., 1890.
+
+  --Pig Iron of Unusual Strength. 18 pp.--Am. Inst. Min. Eng., Oct.,
+       1888.
+
+=Diller, J. S.=
+
+  --Geology of the Taylorville Region of California. 25 pp.,
+       Ill.--Bull. Geol. Soc. Am., Vol. 3. pp. 369-394.
+
+  --Peridotite of Elliott County, Kentucky. 32 pp., Ill.--Bull. U. S.
+       G. S., No. 38.
+
+  --Notes on the Geology of Northern Cal. 224 pp.--Bull. U. S. G. S.,
+       No. 33.
+
+  --Fulgurite from Mt. Thielson, Oregon. 7 pp., Ill.--Am. Jour. Sci.,
+       Oct., 1884.
+
+  --Notes on the Peridotite of Elliot County, Ky. 5 pp.--Am. Jour.
+       Sci., Aug., 1886.
+
+  --A Late Volcanic Eruption in Northern Cal. and its Peculiar Lava.
+       33 pp., XVII pl., 4 cuts.--Bull. U. S. G. S., 79, 1891.
+
+=Emmons, S. F.=
+
+  --Abstract of a Report upon the Geology and Mining Industry of
+       Leadville, Colorado. 90 pp., with maps.--Ann. Rep. U. S. G. S.,
+       1880-81.
+
+  --Orographic Movements in the Rocky Mountains. 22 pp.--Bull. Geol.
+       Soc'y Am., Vol. I., pp 245-86.
+
+  --Notes on the Geology of Butte, Montana. 14 pp.--Trans. Am. Inst.
+       Min. Eng., July, 1887.
+
+  --The Genesis of Certain Ore Deposits. 22 pp.--Trans. Am. Inst. Min.
+       Eng., March, 1886.
+
+  --Structural Relations of Ore Deposits. 36 pp.--Am. Inst. Min. Eng.,
+       Feb., 1888.
+
+  --Notes on the Gold Deposits of Montgomery County, Maryland. 22
+       pp.--Am. Inst. Min. Eng., Feb., 1890.
+
+  --On Glaciers in the Rocky Mountains. 16 pp.--Proc. Col. Sci. Soc'y,
+       1887.
+
+  --Preliminary Notes on Aspen, Col. 26 pp.--Proc. Col. Sci. Soc'y,
+       1887.
+
+  --Fluor-Spar Deposits of Southern Ill. 24 pp, map.--Am. Inst. Min.
+       Eng., Baltimore Meeting, Feb., 1892.
+
+  --The Mining Work of the U. S. Geol. Survey. 13 pp.--Trans. Am. Inst.
+       Min. Eng., Washington Meeting, Feb., 1892.
+
+  --On the Origin of Fissure Veins. 20 pp.--Proc. Col. Sci. Soc'y, 1887.
+
+=Emmons, S. F.= (and =G. E. Becker=).
+
+  --Geological Sketches of the Precious Metal Deposits of the Western
+       United States, with notes on Lead Smelting at Leadville. 296
+       pp.--Tenth Census U. S., Vol. XIII "Statistics and Technology of
+       the Precious Metals."
+
+=Emerson, George H.=
+
+  --Observations on Crystals and Precipitations in Blowpipe Beads. 18
+       pp., Ill.--Proc. Am. Acad. of Arts and Sci., March, 1865.
+
+=Fisher, Rev. O.=
+
+  --Mr. Mallet's Theory of Volcanic Energy Tested. 18 pp.--Phil. Mag.,
+       Oct., 1875.
+
+  --Review of Captain Dutton's Critical Observations on Theories of the
+       Earth's Physical Evolution. 8 pp.--Geol. Mag., Aug., 1876.
+
+  --On the Possibility of Changes in the Latitude of places on the
+       Earth's Surface. Being an appeal to Physicists. 7 pp.--Geol.
+       Mag., July, 1878.
+
+  --On Theories to Account for Glacial Submergence. 8 pp.--Phil. Mag.,
+       Oct., 1892.
+
+  --On Dynamo Metamorphism. 2 pp.--Geol. Mag., July, 1890.
+
+  --On the Warp, its Age and Probable Connection with the last
+       Geological Events. 12 pp., Ill.--Quart. Jour. Geol. Soc'y, Nov.,
+       1866.
+
+  --On Implement-bearing Loams in Suffolk. 5 pp.--Proc. Cambridge Phil.
+       Soc'y, Vol. III, Pt. VII.
+
+  --On the Brocklesham Beds of the Isle of Wight Basin. 30 pp.--Proc.
+       Geol. Soc'y, May, 1862.
+
+  --On a Mammaliferous Deposit at Barrington, near Cambridge. 11 pp.,
+       Ill.--Quart. Journ. Geol. Soc'y, Nov., 1879.
+
+  --On the Denudation of Soft Strata. 4 pp.--Quart. Journ. Geol. Soc'y,
+       Feb., 1861.
+
+  --On the Occurrence of Elephas Meridonalis at Dervlish, Dorset. 8
+       pp., Ill.--Quart. Journ. Geol. Soc'y, Nov., 1888.
+
+  --Glacial Action and Raised Sea-Beds. 4 pp., Ill.--Geol. Mag., April,
+       1873.
+
+  --On the Origin of the Estuary of the Fleet in Dorsetshire.
+
+  --On the Brick-pit at Lexden, near Colchester (with notes on the
+       Coleoptera, by T. U. Wollaston). 9 pp., Ill.--Quart. Journ.
+       Geol. Soc'y of London, 1863.
+
+  --On Faulting, Jointing and Cleavage. 72 pp., Ill.--Geol. Mag., May,
+       1884.
+
+  --Remarks upon Mr. Mallet's Strictures on the Mathematical Test
+       applied to his Theory of Volcanic Energy, by Mr. O. Fisher. 6
+       pp.--Phil. Mag., Feb., 1876.
+
+  --On the Phosphatic Nodules of the Cretaceous Rock of Cambridgeshire.
+       14 pp., 1 pl.--Quart. Journ. Geol. Soc'y, Feb., 1873.
+
+  --On Faults. Reply to Professor Blake's Criticisms. 3 pp.--Geol.
+       Mag., Sept., 1884.
+
+  --"Uniformity" and "Vulcanicity." 3 pp.--Geol. Mag., March, 1875.
+
+  --The Cause of Slaty Cleavage. 4 pp.--Geol. Mag., April, 1885.
+
+  --On the Thermal Conditions and on the Stratification of the
+       Antarctic Ice. 13 pp.--Phil. Mag., June, 1879.
+
+  --On Cleavage and Distortion. 11 pp.--Geol. Mag., Sep., 1884.
+
+  --On the Ages of the "Trail" and "Warp." 7 pp.--Geol. Mag., May, 1867.
+
+  --Review of Dutton's Grand Cañon, Colorado. 4 pp.--Geol. Mag., July,
+       1883.
+
+  --On the Theory of the Erosion of Lake Basins by Glaciers. 2
+       pp.--Geol. Mag., June, 1876.
+
+  --Oblique and Orthogonal Sections of a Folded Plane. 4 pp.,
+       Ill.--Geol. Mag., Jan., 1891.
+
+  --On the Cromer Cliffs. 4 pp., Ill.--Geol. Mag., April, 1880.
+
+  --On Some Natural Pits on the Heaths of Dorsetshire. 2 pp.--Quart.
+       Journ. Geol. Soc'y, London, 1858.
+
+  --On Cirques and Toluses. 4 pp.--Geol. Mag., Jan., 1872.
+
+  --On a Worked Flint from the Buck-Earth of Crayford, Kent. 2
+       pp.--Geol. Mag., June, 1872.
+
+=Frazer, Dr. Persifor.=
+
+  --General Notes on the New Orleans Industrial and Cotton Exhibition.
+       20 pp.--Journal Franklin Institution, June, 1885.
+
+  --The Eozoic and Lower Paleozoic in South Wales and their Comparison
+       with their Appalachian Analogues. 18 pp.--Am. Inst. Min. Engin.,
+       Feb., 1883.
+
+  --Geological and Mineral Studies in Nuevo Leon and Coahuilla, Mexico.
+       36 pp., =III=, and maps.--Am. Inst. Min. Engin., Feb., 1884.
+
+  --Trap Dykes in the Archaean Rocks of Southeastern Pennsylvania. 4
+       pp.--Am. Phil. Soc., Oct. 17, 1884.
+
+  --Classification of Coals. 22 pp.--Trans. Am. Inst. Min. Engin., Vol.
+       VI, 1879.
+
+  --Descriptive Table of Elements. 2 pp.--1891.
+
+  --The late International Geological Congress at Berlin. 4 pp.--Am.
+       Phil. Soc'y, Nov. 20, 1885.
+
+  --Report of the American Committee of the International Congress of
+       Geologists. 5 pp.--Proc. A. A. A. S., Vol. XXXV, August, 1886.
+
+  --General Notes on the Geology of York County, Penn. 20 pp.--Colored
+       maps.
+
+  --On the Physical and Chemical Characteristics of a Trap occurring at
+       Williamson's Point, Penn. 8 pp., 1 colored plate. Read before
+       Am. Phil. Soc'y, Dec. 20, 1878.
+
+  --An Hypothesis of the Structure of the Copper Belt of the South
+       Mountain. 4 pp., Ill.--Trans. Am. Inst. Min. Engin., June, 1883.
+       Read at the Roanoke, Va., Meeting.
+
+  --A Broader Field for the U. S. Geological Survey. 4 pp.--Journ.
+       Franklin Instit., Sept., 1888.
+
+  --The Peach Bottom Slates of the Lower Susquehanna, with sections of
+       the Right and Left Banks. 5 pp., 3 pl.--Am. Inst. Min. Eng.,
+       Oct., 1883.
+
+  --Reply to a paper entitled "Notes on the Geology of Chester Valley
+       and Vicinity." 8 pp.--Journ. Franklin Inst., April, 1884.
+
+  --Mr. Theodore D. Rand's Criticism of Vol. C_{4} Geology of Chester
+       County, Penn. 6 pp.--Journ. Franklin Inst., Oct., 1883.
+
+  --Archaean Characters of the Rocks of the Nucleal Ranges of the
+       Antilles. 1 p.--Brit. Assn., 1888.
+
+  --Notes on Fresh-Water Wells of the Atlantic Beach. 4 pp.--Journ.
+       Franklin Inst., Sept., 1890.
+
+  --The Position of the American New Red Sandstone. 8 pp.--Trans. Am.
+       Inst. Min. Engin., Vol. V.
+
+  --On the Traps of the Mesozoic Sandstone in York and Adams Counties,
+       Penn. 13 pp., 4 pl.--Am. Phil. Soc'y, April 16, 1875.
+
+  --The Whopper Lode, Gunnison County, Colo. 10 pp.--Am. Inst. Min.
+       Engin., Aug., 1880.
+
+  --Some Copper Deposits of Carroll County, Md. 8 pp., 1 pl.--Am. Inst.
+       Min. Engin., Aug., 1880.
+
+  --A Convenient Device to be Applied to the Hand Compass. 1 p.--Am.
+       Phil. Soc'y, Dec. 5, 1884.
+
+  --The Approaches to a Theory of the Causes of Magnetic Declination.
+       16 pp.--Am. Phil. Soc'y, Apr. 6, 1877.
+
+  --On Improvement in the Construction of the Hypsometric Aneroid.--Am.
+       Phil. Soc'y, March 2, 1883.
+
+  --An Exfoliation of Rocks near Gettysburg. 2 pp.--Am. Phil. Soc'y,
+       Dec. 4, 1874.
+
+  --Note on the New Geological Map of Europe. 6 pp.--Trans. Am. Inst.
+       Min. Engin.
+
+  --Some Supposed Fossils from the Susquehanna River, just South of the
+       Pennsylvania-Maryland Line. 3 pp., 1 pl.--Proc. Am. Phil. Soc'y
+       XVIII, Sept. 18, 1879.
+
+  --Missing Ores of Iron. 12 pp., Ill.--Trans. Am. Inst. Min. Engin.,
+       Vol. VI, 1879.
+
+  --The Peach Bottom Slates of Southeastern York and Southern Lancaster
+       Counties, Penn. 5 pp., 1. pl.--Trans. Am. Inst. Mining Engin.,
+       1883.
+
+  --A Speculation on Protoplasm. 7 pp.--Am Nat., July, 1876.
+
+  --A Mirror for Illuminating Opaque Objects for the Projecting
+       Microscope. 2 pp.--Am. Phil. Soc'y, Feb. 20, 1880.
+
+  --The Progress of Chemical Theory; Its Helps and Hindrances. 37
+       pp.--Journ. Franklin Instit., Apr., May and June, 1891.
+
+  --Mineral Formulæ. 6 pp.--Proc. Acad. Nat. Sci., Phila., July 7, 1874.
+
+  --Notes from the Literature on the Geology of Egypt, and Examination
+       of the Syenitic Granite of the Obelisk which Lieut. Comd'r
+       Gorringe, U. S. N., brought to New York. 27 pp., 4 pl.--Trans.
+       Am. Inst. Mining Engin., 1883.
+
+  --Report of Committee on the International Congress of Geologists. 3
+       pp.--Proc. A. A. A. S., Vol. XXXIX, 1890.
+
+  --On Certain Trap Rocks from Brazil. 3 pp.--Proc. Acad. Sci., Phila.,
+       1876.
+
+  --An Unjust Attack. 8 pp.--Am. Geol., Jan., 1889.
+
+  --The Philadelphia Meeting of the International Congress of
+       Geologists. 10 pp., Am. Geol., June, 1890.
+
+  --Report of the Berlin International Geological Congress. 13 pp.--Am.
+       Jour. Sci., XXX, December, 1885.
+
+  --Mesozoic Sandstone of the Atlantic Slope. 9 pp.--Am. Nat., May,
+       1879.
+
+  --Archæan-Paleozoic Contact near Philadelphia, Penn. 6 pp., 1
+       pl.--Proc. A. A. A. S., Vol. XXXIII, Sept., 1884.
+
+  --Report of the Sub-Committee of the Berlin Congress of Geologists on
+       the Archæan. 80 pp.
+
+  --Crystallization. 11 pp., Ill.--Journal Franklin Inst., Aug., 1885.
+
+  --Origin of the Lower Silurian Limonites of York and Adams Counties,
+       6 pp.--Am. Phil. Soc'y, March 19, 1875.
+
+  --The Northern Serpentine Belt in Chester County, Pa. 8 pp.--Trans.
+       Am. Inst. Min. Engin., 1883.
+
+  --The Persistence of Plant and Animal Life under Changing Conditions
+       of Environment. 13 pp.--Am. Nat., June, 1890.
+
+  --International Congress of Geologists, 1886. 109 pp., 1 pl.
+
+  --International Congress of Geologists, Reports of the Sub-Committee
+       appointed by the American Committee. 239 pp., 1888.
+
+  --Other Short Articles.
+
+=Frisbie, Dr. J. F.=
+
+  --Glacial Moraines. 16 pp.
+
+  --Mountain Building and Mountain Sculpture. 13 pp.
+
+  --The Franconia Flume, the Causes that led to its Formation. 8 pp.
+
+  --Planet Building. 11 pp., 1 pl.
+
+  --   "      "      17 pp., 2 pl.
+
+=Geikie, Sir Archibald=, LL.D., D.Sc, F.R.S.E., P.G.S.
+
+  --Address to the Geological Section of the British Association. 23 pp.
+
+  --Address by Sir Archibald Geikie, President of British Association
+       for the Advancement of Science. 1892. 24 pp.
+
+  --Progress of the Geological Survey in Scotland. 10 pp.--Proc. Royal
+       Soc'y, Edinburgh, Vol. II, Session 1864-5.
+
+  --On the Tertiary Volcanic Rocks of the British Islands. 4 pp.--Proc.
+       Royal Soc'y, Edinburgh, 1866-67.
+
+  --The History of Volcanic Action during the Tertiary Period in the
+       British Islands (Abstract). 5 pp.--Proc. Royal Soc'y, Edin.,
+       1888.
+
+  --Address delivered at the 36th Anniversary Meeting of the Edinburgh
+       Geological Society. Also Notes for a Comparison of the Volcanic
+       Geology of Central Scotland with that of Auvergne and the Eifel.
+       16 pp.--Trans. of the Edinburgh Geological Society, 1869-70,
+       Vol. II, Part I.
+
+  --On Modern Denudation. 38 pp.--Trans. Geol. Soc'y of Glasgow, Vol.
+       III, p. 153.
+
+  --On Denudation now in Progress. 6 pp.--Geol. Mag., Vol. I, No. 6,
+       June, 1868.
+
+  --Earth Sculpture and the Huttonian School of Geology. The Inaugural
+       Address Delivered at the 40th Anniversary Meeting of the
+       Edinburgh Geological Society, Nov. 6, 1873.
+
+  --Recent Researches into the Origin and Age of the Highlands of
+       Scotland and the West of Ireland. 19 pp.
+
+  --Royal Institute of Great Britain, 1889.
+
+  --The Cañons of the Far West.--Ibid., April 6, 1883. 4 pp.
+
+  --Rock-Weathering, as illustrated in Edinburgh Churchyards. 15 pp., 1
+       pl.--Proc. Royal Soc'y, Edinburgh, Vol. X., April 19, 1880.
+
+  --The Ancient Glaciers of the Rocky Mountains. 7 pp.--Am. Nat. Jan.
+       1881.
+
+  --The Ice Age in Britain.--Science Lectures for the People. 17 pp.
+
+  --The Old Man of Hoy. 6 pp., 1 pl.--Report Brit. Assoc., 1871.
+
+  --On the Old Red Sandstone of the South of Scotland. 12 pp., 1
+       pl.--Quarterly Journal Geol. Soc'y, Aug. 1860.
+
+  --On the Geology of Strath, Skye, (with descriptions of some Fossils
+       from Skye, by T. Wright, M.D., F.R.S.E.) 36 pp., 1 pl.
+
+  --The History of Volcanic Action in the Area of the British Isles.
+       119 pp.--Quarterly Journal of the Geological Society of London,
+       Vol. XLVIII, 1892.
+
+  --On the Supposed Pre-Cambrian Rocks of St. David's. 66 pp., 3
+       pl.--Quarterly Journal of the Geological Society, Aug. 1883.
+
+  --On the Tertiary Volcanic Rocks of the British Islands. 31 pp., 1 pl.
+
+  --The Geological Origin of the Present Scenery of Scotland. 21 pp.
+       Ill.--The Journal of Travel and Natural History.
+
+  --On the Age of the Altered Limestone of Strath, Skye.--13 pp.
+       Ill.--Quart. Journal Geol. Soc'y, 1888.
+
+  --Address of the President of the Geological Society of London, Feb.
+       20, 1891. 126 pp.
+
+  --The Origin of Coral Reefs. 13 pp. Ill.--Proc. Royal Physical Soc'y.
+       Vol. VIII, p.; 1884.
+
+  --The "Pitchstone" of Eskdale, a retrospect and comparison of
+       Geological Methods. Ibid, Vol V, 1880.
+
+=Genth, F. A.=
+
+  --Ueber Nordamerikanische Tellur-und Wismuth-Mineralien. 14
+       pp.--Journal für Praktische Chemie, 1874.
+
+  --Ueber Lansfordit, Nesquehonit und Pseudomorphosen von Nesquehonit
+       nach Lansfordit. (F. A. Genth und S. L. Penfield). 18 pp., 1
+       pl.--Zeit. für Krystallographie, 1890.
+
+  --Contributions to Mineralogy. 18 pp., 1 pl. Read before Am. Phil.
+       Soc'y, Oct. 2, 1885.
+
+  --do. 21 pp. Read before Am. Phil. Soc'y, March 18, 1887.
+
+  --Investigation of Iron Ores and Limestones from Blair and Huntingdon
+       counties, Pa. 26 pp.--Read before the Am. Phil. Soc'y, Feb. 6,
+       1874.
+
+  --Contributions to Mineralogy. 6 pp.--Am. Jour. Sci., Sept. 1889; 4
+       pp. Jan., 1890.
+
+  --do. with Crystallographic notes by S. L. Penfield. 9 pp.--Am. Jour.
+       Sci., Sept., 1890; 10 pp. May, 1891: 6 pp. March, 1892.
+
+  --On American Tellurium and Bismuth Minerals. 9 pp.--Am. Phil. Soc'y,
+       Aug. 21, 1874.
+
+  --On Herderite. 7 pp. Read before Am. Phil. Soc'y, Oct. 17, 1884.
+
+  --On Lansfordite, Nesquehonite, a New Mineral and Pseudomorphs of
+       Nesquehonite after Lansfordite. 17 pp., 1 pl.--Am. Jour. Sci.,
+       Feb., 1890.
+
+  --The Minerals of North Carolina.--Bulletin 74, U. S. G. S. 120 pp.
+
+  --The Minerals and Mineral Localities of North Carolina. 122
+       pp.--Geol. of North Carolina, Vol. II, 1881.
+
+  --First Annual Report of Dr. F. A. Genth, Chemist of the Pennsylvania
+       Board of Agriculture. 32 pp., 1878.
+
+  --Second Preliminary Report on the Mineralogy of Pennsylvania, with
+       Analyses of Mineral Spring Waters. 38 pp.
+
+  --Ueber einige Tellur-und Vanad-Mineralien. 13 pp.--Zeit. für
+       Krystallographie, etc., 1877.
+
+  --On the Equivalent of Cerium by the late Dr. Charles Wolf. 10
+       pp.--Am. Jour. Sci., May, 1868.
+
+  --Contributions to Mineralogy, No. 54; (with Crystallographic Notes
+       by S. L. Penfield). 9 pp.--Am. Jour. Sci., Nov., 1892.
+
+  --On Penfieldite, a new species. 1 pp.--Am. Jour. Sci., Sept., 1892.
+
+  --Mineralogische Mittheilungen, by F. A. Genth (with Crystallographic
+       Notes by S. L. Penfield). 10 pp. Ill.--"Zeit. für Krystallog."
+       XVIII, 6, (1891).
+
+  --Examination of the North Carolina Uranium Minerals. 7 pp.--Am.
+       Chem. Jour. Vol. I, Nos. 2 and 3.
+
+  --On some American Vanadium Minerals. 6 pp.--Am. Jour. Sci., July,
+       1876.
+
+  --On an undescribed Meteoric Iron from East Tennessee. 4 pp., 2
+       pl.--Proc. Acad. Nat. Sci. Phila., Dec. 28, 1886.
+
+  --Lansfordit, ein neues Mineral, 2 pp.
+
+  --On the Vanadates and Iodyrite, from Lake Valley, Sierra Co., New
+       Mexico. 13 pp. Read before Am. Phil. Soc'y Apr. 17, 1885.
+
+  --Contributions to Mineralogy.--Am. Jour. Sci., Sept. 1859; March,
+       1862, May, 1868.
+
+  --Meteorology. 6 pp.
+
+  --Meteorology. 4 pp.--Am. Jour. Sci., Nov., 1861.
+
+  --Re-examination of the Tetradymite from Field's Gold Mine, Georgia.
+
+  --On Pyrophyllite from Schuylkill Co., Penn. Read before Am. Phil.
+       Soc'y, July 18, 1878.
+
+  --Mineralogische Mittheilungen. 31 pp., 2 pl.--Zeit. für
+       Krystallographie, 1885.
+
+  --Jarosite from Utah. 1 p.--Am. Jour. Sci., Jan., 1890.
+
+  --On Two Minerals from Delaware Co., Pa. 3 pp.--Proc. Acad. Sci. of
+       Phila., 1889.
+
+  --Contributions from the Laboratory of the University of Pennsylvania.
+
+=Gilbert, G. K.=
+
+  --The Colorado Plateau Region considered as a Field for Geological
+       Study. 27 pp.--Am. Jour. Sci., July and August, 1876.
+
+  --The Strength of the Earth's Crust. 5 pp.--Bull. Geol. Soc. Am. Vol.
+       I, 1889.
+
+  --The History of the Niagara River. 24 pp., 8 pl.--Sixth An. Rept. of
+       Com. of State Reservation at Niagara, 1889.
+
+  --The Work of the International Congress of Geologists. 22 pp.--Am.
+       Jour. Sci., Dec, 1887.
+
+  --The Sufficiency of Terrestrial Rotation for the Deflection of
+       Streams. 6 pp.--Nat. Acad. Sci., 1884.
+
+=Gordon, C. H.=
+
+  --Observations on the Keokuk Species of Agaricocrinus. 7 pp., 1
+       pl.--Am. Geol., May, 1890.
+
+  --On the Brecciated Character of the St. Louis Limestone. 9 pp., 2
+       pl.--Am. Nat., April, 1890.
+
+  --Proceedings of the Iowa Academy of Sciences for 1887, 1889, 1889.
+       101 pp.
+
+  --Quaternary Geology of Keokuk, Iowa, with Notes on the Underlying
+       Rock Structure. 8 pp., 2 pl.
+
+=Grant, Uly. S.=
+
+  --Notes on the Molluscan Fauna of Minnesota. 4 pp.--16th An. Rept.
+       Geol. and Nat. Hist. Survey, Minn. (1887).
+
+  --Account of a Deserted Gorge of the Mississippi near Minnehaha
+       Falls. 6 pp., 1 pl.
+
+  --Conchological Notes. 12 pp.--14th An. Rept. Geol. and Nat. Hist.
+       Survey, Minn.
+
+  --The Stratigraphical Position of the Ogishke Conglomerate of
+       Northeastern Minnesota. 8 pp.--Am. Geol. Vol. X, July, 1892.
+
+  --Report of Geological Observations made in Northeastern Minnesota
+       during the Summer of 1888. 67 pp.--Geol. and Nat. Hist. Survey
+       of Minn.; part IV. 17th An. Rept.
+
+=Hall, C. W.=
+
+  --Notes on a Geological Excursion into Central Wisconsin. 18 pp., 1
+       pl.
+
+=Hallock, William.=
+
+  --Chemical Action between Solids. 4 pp.--Am. Jour. Sci., May, 1889.
+
+  --The Flow of Solids or the Behavior of Solids under High Pressure. 8
+       pp.--Bull. U. S. G. S., No. 55.
+
+  --Ueber die Lichtgeschwindigkeit in verschiedenen Quartzflächen. 3
+       pp.--Annalen der Physik und Chemie, 1881. Bd. XII.
+
+  --Preliminary Report of Observations at the Deep Well at Wheeling, W.
+       Va.--Proc. A. A. A. S., 1891, vol. XL.
+
+=Harden, John Hy.=, M. E.
+
+  --Rock Salt Deposit of Huron and Bruce Counties, Ontario, Canada. 6
+       pp.--Proc. Engineer's Club. Phila., Vol. I, No. 3.
+
+  --The Construction of Maps in Relief. 23 pp., Ill., 1 pl.--Trans. Am.
+       Inst. Min. Eng., 1887.
+
+=Harpe, Phil. de la.=
+
+  --Description des Nummulites appartenant à la Zone supérieure des
+       Falaises de Biarritz. 20 pp., 1 pl.--Bulletin de la Société de
+       Borda, 1879.
+
+  --Une Échelle des Nummulites ou Tableau de la distribution
+       stratigraphique des Espèces de Nummulites. 5
+       pp.--"Verhandlungen" de la Soc. Helv. des Sc. Nat., session de
+       St. Gall, 1879.
+
+  --Note sur les Nummulites des Alpes occidentales. 6 pp.--Extrait des
+       actes de la Soc. Helv. des Sc. Nat., 1877.
+
+  --Note sur les Nummulites des environs de Nice et de Menton. 22 pp.,
+       1 pl.--Bulletin de la Société Geologique de France, Octobre,
+       1877.
+
+  --Ossements appartenant à L'Anthracotherium Magnum recueillis dans
+       les Lignites des environs de Lausanne. 14 pp.--Bulletin de la
+       Soc. vaud. des Sc. Nat., 1854.
+
+  --Note sur la Géologie des environs de Louèche-les-Bains. 32 pp., 1
+       pl.--Bulletin de la Soc. vaud. des Sc. Nat., 1877.
+
+  --Étude sur les Nummulites du Comté de Nice suivie d'une Échelle des
+       Nummulites ou Tableau de la distribution stratigraphique des
+       Espèces de ce genre. 44 pp., 1 pl.--Bulletin de la Soc. vaud.
+       des Sc. Nat.
+
+  --Nummulites des Alpes Francaises. 26 pp.--Bulletin de la Soc. vaud.
+       Sc. Nat. XVI, 82.
+
+  --Description des Nummulites des Falaises de Biarritz. 16 pp., 1
+       pl.--Extrait du Bulletin de la Société de Borda, 1881.
+
+  --Description des Nummulites appartenant à la Zone inférieure des
+       Falaises de Biarritz des environs de la Villa Bruce jusqu'à
+       Handia. 44 pp.--Bulletin de la Société de Borda, 1881.
+
+  --Description des Nummulites appartenant à la Zone moyenne des
+       Falaises de Biarritz. 8 pp., Ill.--Bulletin de la Société de
+       Borda, 1880.
+
+=Hayes, C. Willard.=
+
+  --The Overthrust Faults of the Southern Appalachians. 14 pp., 2
+       pl.--Bulletin Geol. Soc. Am., Vol. II, pp. 141-154.
+
+  --Report on the Geology of Northeastern Alabama and Adjacent Portions
+       of Georgia and Tennessee. 84 pp., 1 pl., 1 map.--Bulletin No. 4,
+       Geol. Surv. of Alabama.
+
+  --An Expedition through the Yukon District. 46 pp., 3 maps.--Nat.
+       Geog. Mag.
+
+=Heyes, J. F.=, M.A.
+
+  --Aspects of Imperial Federation. 8 pp.
+
+  --Scientific Aspects of Imperial Unity.--European Mail.
+
+  --The Recognition of Geography. 7 pp.
+
+
+(_Further acknowledgments of pamphlets and of specimens will be made in
+the next issue._)
+
+
+       *       *       *       *       *
+
+
+Transcriber Note
+
+
+Illustrations were moved so as to not split paragraphs. Minor errors
+were corrected.
+
+
+
+
+
+End of the Project Gutenberg EBook of The Journal of Geology,
+January-February 1893, by Various
+
+*** END OF THE PROJECT GUTENBERG EBOOK 59611 ***