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diff --git a/2922.txt b/2922.txt new file mode 100644 index 0000000..f4a80d1 --- /dev/null +++ b/2922.txt @@ -0,0 +1,1008 @@ +Project Gutenberg's The Past Condition of Organic Nature, by Thomas H. Huxley + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Past Condition of Organic Nature + Lecture II. (of VI.), Lectures To Working Men, at the + Museum of Practical Geology, 1863, On Darwin's work: "Origin + of Species". + +Author: Thomas H. Huxley + +Posting Date: January 4, 2009 [EBook #2922] +Release Date: November, 2001 + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK CONDITION OF ORGANIC NATURE *** + + + + +Produced by Amy E. Zelmer + + + + + +THE PAST CONDITION OF ORGANIC NATURE + +Lecture II. (of VI.), Lectures To Working Men, at the Museum of +Practical Geology, 1863, On Darwin's work: "Origin of Species". + + +by Thomas H. Huxley + + + + +IN the lecture which I delivered last Monday evening, I endeavoured to +sketch in a very brief manner, but as well as the time at my disposal +would permit, the present condition of organic nature, meaning by +that large title simply an indication of the great, broad, and general +principles which are to be discovered by those who look attentively at +the phenomena of organic nature as at present displayed. The general +result of our investigations might be summed up thus: we found that the +multiplicity of the forms of animal life, great as that may be, may be +reduced to a comparatively few primitive plans or types of construction; +that a further study of the development of those different forms +revealed to us that they were again reducible, until we at last brought +the infinite diversity of animal, and even vegetable life, down to the +primordial form of a single cell. + +We found that our analysis of the organic world, whether animals or +plants, showed, in the long run, that they might both be reduced into, +and were, in fact, composed of, the same constituents. And we saw +that the plant obtained the materials constituting its substance by +a peculiar combination of matters belonging entirely to the inorganic +world; that, then, the animal was constantly appropriating the +nitrogenous matters of the plant to its own nourishment, and returning +them back to the inorganic world, in what we spoke of as its waste; and +that finally, when the animal ceased to exist, the constituents of its +body were dissolved and transmitted to that inorganic world whence they +had been at first abstracted. Thus we saw in both the blade of grass and +the horse but the same elements differently combined and arranged. We +discovered a continual circulation going on,--the plant drawing in the +elements of inorganic nature and combining them into food for the animal +creation; the animal borrowing from the plant the matter for its own +support, giving off during its life products which returned immediately +to the inorganic world; and that, eventually, the constituent materials +of the whole structure of both animals and plants were thus returned to +their original source: there was a constant passage from one state of +existence to another, and a returning back again. + +Lastly, when we endeavoured to form some notion of the nature of the +forces exercised by living beings, we discovered that they--if +not capable of being subjected to the same minute analysis as the +constituents of those beings themselves--that they were correlative +with--that they were the equivalents of the forces of inorganic +nature--that they were, in the sense in which the term is now used, +convertible with them. That was our general result. + +And now, leaving the Present, I must endeavour in the same manner to put +before you the facts that are to be discovered in the Past history of +the living world, in the past conditions of organic nature. We have, +to-night, to deal with the facts of that history--a history involving +periods of time before which our mere human records sink into utter +insignificance--a history the variety and physical magnitude of whose +events cannot even be foreshadowed by the history of human life and +human phenomena--a history of the most varied and complex character. + +We must deal with the history, then, in the first place, as we should +deal with all other histories. The historical student knows that his +first business should be to inquire into the validity of his evidence, +and the nature of the record in which the evidence is contained, that +he may be able to form a proper estimate of the correctness of the +conclusions which have been drawn from that evidence. So, here, we must +pass, in the first place, to the consideration of a matter which may +seem foreign to the question under discussion. We must dwell upon the +nature of the records, and the credibility of the evidence they contain; +we must look to the completeness or incompleteness of those records +themselves, before we turn to that which they contain and reveal. The +question of the credibility of the history, happily for us, will not +require much consideration, for, in this history, unlike those of human +origin, there can be no cavilling, no differences as to the reality and +truth of the facts of which it is made up; the facts state themselves, +and are laid out clearly before us. + +But, although one of the greatest difficulties of the historical student +is cleared out of our path, there are other difficulties--difficulties +in rightly interpreting the facts as they are presented to us--which +may be compared with the greatest difficulties of any other kinds of +historical study. + +What is this record of the past history of the globe, and what are the +questions which are involved in an inquiry into its completeness or +incompleteness? That record is composed of mud; and the question which +we have to investigate this evening resolves itself into a question +of the formation of mud. You may think, perhaps, that this is a +vast step--of almost from the sublime to the ridiculous--from the +contemplation of the history of the past ages of the world's existence +to the consideration of the history of the formation of mud! But, +in nature, there is nothing mean and unworthy of attention; there +is nothing ridiculous or contemptible in any of her works; and this +inquiry, you will soon see, I hope, takes us to the very root and +foundations of our subject. + +How, then, is mud formed? Always, with some trifling exception, which +I need not consider now--always, as the result of the action of water, +wearing down and disintegrating the surface of the earth and rocks with +which it comes in contact--pounding and grinding it down, and carrying +the particles away to places where they cease to be disturbed by this +mechanical action, and where they can subside and rest. For the ocean, +urged by winds, washes, as we know, a long extent of coast, and every +wave, loaded as it is with particles of sand and gravel as it breaks +upon the shore, does something towards the disintegrating process. And +thus, slowly but surely, the hardest rocks are gradually ground down to +a powdery substance; and the mud thus formed, coarser or finer, as the +case may be, is carried by the rush of the tides, or currents, till it +reaches the comparatively deeper parts of the ocean, in which it can +sink to the bottom, that is, to parts where there is a depth of about +fourteen or fifteen fathoms, a depth at which the water is, usually, +nearly motionless, and in which, of course, the finer particles of this +detritus, or mud as we call it, sinks to the bottom. + +Or, again, if you take a river, rushing down from its mountain sources, +brawling over the stones and rocks that intersect its path, loosening, +removing, and carrying with it in its downward course the pebbles and +lighter matters from its banks, it crushes and pounds down the rocks and +earths in precisely the same way as the wearing action of the sea waves. +The matters forming the deposit are torn from the mountain-side and +whirled impetuously into the valley, more slowly over the plain, thence +into the estuary, and from the estuary they are swept into the sea. The +coarser and heavier fragments are obviously deposited first, that is, +as soon as the current begins to lose its force by becoming amalgamated +with the stiller depths of the ocean, but the finer and lighter +particles are carried further on, and eventually deposited in a deeper +and stiller portion of the ocean. + +It clearly follows from this that mud gives us a chronology; for it is +evident that supposing this, which I now sketch, to be the sea bottom, +and supposing this to be a coast-line; from the washing action of the +sea upon the rock, wearing and grinding it down into a sediment of mud, +the mud will be carried down, and at length, deposited in the deeper +parts of this sea bottom, where it will form a layer; and then, while +that first layer is hardening, other mud which is coming from the same +source will, of course, be carried to the same place; and, as it is +quite impossible for it to get beneath the layer already there, it +deposits itself above it, and forms another layer, and in that way you +gradually have layers of mud constantly forming and hardening one above +the other, and conveying a record of time. + +It is a necessary result of the operation of the law of gravitation that +the uppermost layer shall be the youngest and the lowest the oldest, and +that the different beds shall be older at any particular point or spot +in exactly the ratio of their depth from the surface. So that if they +were upheaved afterwards, and you had a series of these different layers +of mud, converted into sandstone, or limestone, as the case might be, +you might be sure that the bottom layer was deposited first, and that +the upper layers were formed afterwards. Here, you see, is the first +step in the history--these layers of mud give us an idea of time. + +The whole surface of the earth,--I speak broadly, and leave out minor +qualifications,--is made up of such layers of mud, so hard, the majority +of them, that we call them rock whether limestone or sandstone, or other +varieties of rock. And, seeing that every part of the crust of the earth +is made up in this way, you might think that the determination of the +chronology, the fixing of the time which it has taken to form this crust +is a comparatively simple matter. Take a broad average, ascertain how +fast the mud is deposited upon the bottom of the sea, or in the estuary +of rivers; take it to be an inch, or two, or three inches a year, or +whatever you may roughly estimate it at; then take the total thickness +of the whole series of stratified rocks, which geologists estimate at +twelve or thirteen miles, or about seventy thousand feet, make a sum +in short division, divide the total thickness by that of the quantity +deposited in one year, and the result will, of course, give you the +number of years which the crust has taken to form. + +Truly, that looks a very simple process! It would be so except for +certain difficulties, the very first of which is that of finding how +rapidly sediments are deposited; but the main difficulty--a difficulty +which renders any certain calculations of such a matter out of the +question--is this, the sea-bottom on which the deposit takes place is +continually shifting. + +Instead of the surface of the earth being that stable, fixed thing that +it is popularly believed to be, being, in common parlance, the very +emblem of fixity itself, it is incessantly moving, and is, in fact, +as unstable as the surface of the sea, except that its undulations are +infinitely slower and enormously higher and deeper. + +Now, what is the effect of this oscillation? Take the case to which +I have previously referred. The finer or coarser sediments that are +carried down by the current of the river, will only be carried out a +certain distance, and eventually, as we have already seen, on reaching +the stiller part of the ocean, will be deposited at the bottom. + +Let C y (Fig. 4) be the sea-bottom, y D the shore, x y the sea-level, +then the coarser deposit will subside over the region B, the finer over +A, while beyond A there will be no deposit at all; and, consequently, no +record will be kept, simply because no deposit is going on. Now, suppose +that the whole land, C, D, which we have regarded as stationary, goes +down, as it does so, both A and B go further out from the shore, which +will be at y1; x1, y1, being the new sea-level. The consequence will be +that the layer of mud (A), being now, for the most part, further than +the force of the current is strong enough to convey even the finest +'debris', will, of course, receive no more deposits, and having attained +a certain thickness will now grow no thicker. + +We should be misled in taking the thickness of that layer, whenever it +may be exposed to our view, as a record of time in the manner in which +we are now regarding this subject, as it would give us only an imperfect +and partial record: it would seem to represent too short a period of +time. + +[Illustration: Fig.4.] + +Suppose, on the other hand, that the land (C D) had gone on rising +slowly and gradually--say an inch or two inches in the course of a +century,--what would be the practical effect of that movement? Why, that +the sediment A and B which has been already deposited, would eventually +be brought nearer to the shore-level, and again subjected to the wear +and tear of the sea; and directly the sea begins to act upon it, it +would of course soon cut up and carry it away, to a greater or less +extent, to be re-deposited further out. + +Well, as there is, in all probability, not one single spot on the whole +surface of the earth, which has not been up and down in this way a great +many times, it follows that the thickness of the deposits formed at any +particular spot cannot be taken (even supposing we had at first obtained +correct data as to the rate at which they took place) as affording +reliable information as to the period of time occupied in its deposit. +So that you see it is absolutely necessary from these facts, seeing that +our record entirely consists of accumulations of mud, superimposed one +on the other; seeing in the next place that any particular spots on +which accumulations have occurred, have been constantly moving up and +down, and sometimes out of the reach of a deposit, and at other times +its own deposit broken up and carried away, it follows that our record +must be in the highest degree imperfect, and we have hardly a trace +left of thick deposits, or any definite knowledge of the area that they +occupied, in a great many cases. And mark this! That supposing even +that the whole surface of the earth had been accessible to the +geologist,--that man had had access to every part of the earth, and had +made sections of the whole, and put them all together,--even then his +record must of necessity be imperfect. + +But to how much has man really access? If you will look at this Map you +will see that it represents the proportion of the sea to the earth: this +coloured part indicates all the dry land, and this other portion is the +water. You will notice at once that the water covers three-fifths of the +whole surface of the globe, and has covered it in the same manner ever +since man has kept any record of his own observations, to say nothing of +the minute period during which he has cultivated geological inquiry. +So that three-fifths of the surface of the earth is shut out from us +because it is under the sea. Let us look at the other two-fifths, +and see what are the countries in which anything that may be termed +searching geological inquiry has been carried out: a good deal of +France, Germany, and Great Britain and Ireland, bits of Spain, of +Italy, and of Russia, have been examined, but of the whole great mass of +Africa, except parts of the southern extremity, we know next to nothing; +little bits of India, but of the greater part of the Asiatic continent +nothing; bits of the Northern American States and of Canada, but of +the greater part of the continent of North America, and in still larger +proportion, of South America, nothing! + +Under these circumstances, it follows that even with reference to that +kind of imperfect information which we can possess, it is only of about +the ten-thousandth part of the accessible parts of the earth that has +been examined properly. Therefore, it is with justice that the most +thoughtful of those who are concerned in these inquiries insist +continually upon the imperfection of the geological record; for, I +repeat, it is absolutely necessary, from the nature of things, that +that record should be of the most fragmentary and imperfect character. +Unfortunately this circumstance has been constantly forgotten. Men of +science, like young colts in a fresh pasture, are apt to be exhilarated +on being turned into a new field of inquiry, to go off at a hand-gallop, +in total disregard of hedges and ditches, losing sight of the real +limitation of their inquiries, and to forget the extreme imperfection of +what is really known. Geologists have imagined that they could tell us +what was going on at all parts of the earth's surface during a given +epoch; they have talked of this deposit being contemporaneous with +that deposit, until, from our little local histories of the changes at +limited spots of the earth's surface, they have constructed a universal +history of the globe as full of wonders and portents as any other story +of antiquity. + +But what does this attempt to construct a universal history of the globe +imply? It implies that we shall not only have a precise knowledge of the +events which have occurred at any particular point, but that we shall +be able to say what events, at any one spot, took place at the same time +with those at other spots. + +Let us see how far that is in the nature of things practicable. Suppose +that here I make a section of the Lake of Killarney, and here the +section of another lake--that of Loch Lomond in Scotland for instance. +The rivers that flow into them are constantly carrying down deposits of +mud, and beds, or strata, are being as constantly formed, one above the +other, at the bottom of those lakes. Now, there is not a shadow of +doubt that in these two lakes the lower beds are all older than the +upper--there is no doubt about that; but what does 'this' tell us about +the age of any given bed in Loch Lomond, as compared with that of any +given bed in the Lake of Killarney? It is, indeed, obvious that if +any two sets of deposits are separated and discontinuous, there is +absolutely no means whatever given you by the nature of the deposit of +saying whether one is much younger or older than the other; but you may +say, as many have said and think, that the case is very much altered if +the beds which we are comparing are continuous. Suppose two beds of mud +hardened into rock,--A and B-are seen in section. (Fig. 5.) + +[Illustration: Fig. 5.] + +Well, you say, it is admitted that the lowermost bed is always the +older. Very well; B, therefore, is older than A. No doubt, 'as a whole', +it is so; or if any parts of the two beds which are in the same vertical +line are compared, it is so. But suppose you take what seems a very +natural step further, and say that the part 'a' of the bed A is younger +than the part 'b' of the bed B. Is this sound reasoning? If you find any +record of changes taking place at 'b', did they occur before any events +which took place while 'a' was being deposited? It looks all very plain +sailing, indeed, to say that they did; and yet there is no proof of +anything of the kind. As the former Director of this Institution, Sir +H. De la Beche, long ago showed, this reasoning may involve an entire +fallacy. It is extremely possible that 'a' may have been deposited ages +before 'b'. It is very easy to understand how that can be. To return +to Fig. 4; when A and B were deposited, they were 'substantially' +contemporaneous; A being simply the finer deposit, and B the coarser +of the same detritus or waste of land. Now suppose that that sea-bottom +goes down (as shown in Fig. 4), so that the first deposit is carried +no farther than 'a', forming the bed Al, and the coarse no farther +than 'b', forming the bed B1, the result will be the formation of two +continuous beds, one of fine sediment (A A1) over-lapping another of +coarse sediment (B B1). Now suppose the whole sea-bottom is raised up, +and a section exposed about the point Al; no doubt, 'at this spot', the +upper bed is younger than the lower. But we should obviously greatly err +if we concluded that the mass of the upper bed at A was younger than +the lower bed at B; for we have just seen that they are contemporaneous +deposits. Still more should we be in error if we supposed the upper bed +at A to be younger than the continuation of the lower bed at Bl; for +A was deposited long before B1. In fine, if, instead of comparing +immediately adjacent parts of two beds, one of which lies upon another, +we compare distant parts, it is quite possible that the upper may be any +number of years older than the under, and the under any number of years +younger than the upper. + +Now you must not suppose that I put this before you for the purpose of +raising a paradoxical difficulty; the fact is, that the great mass of +deposits have taken place in sea-bottoms which are gradually sinking, +and have been formed under the very conditions I am here supposing. + +Do not run away with the notion that this subverts the principle I +laid down at first. The error lies in extending a principle which is +perfectly applicable to deposits in the same vertical line to deposits +which are not in that relation to one another. + +It is in consequence of circumstances of this kind, and of others that I +might mention to you, that our conclusions on and interpretations of +the record are really and strictly only valid so long as we confine +ourselves to one vertical section. I do not mean to tell you that there +are no qualifying circumstances, so that, even in very considerable +areas, we may safely speak of conformably superimposed beds being older +or younger than others at many different points. But we can never be +quite sure in coming to that conclusion, and especially we cannot +be sure if there is any break in their continuity, or any very great +distance between the points to be compared. + +Well now, so much for the record itself,--so much for its +imperfections,--so much for the conditions to be observed in +interpreting it, and its chronological indications, the moment we pass +beyond the limits of a vertical linear section. + +Now let us pass from the record to that which it contains,--from the +book itself to the writing and the figures on its pages. This writing +and these figures consist of remains of animals and plants which, in the +great majority of cases, have lived and died in the very spot in which +we now find them, or at least in the immediate vicinity. You must all of +you be aware--and I referred to the fact in my last lecture--that there +are vast numbers of creatures living at the bottom of the sea. These +creatures, like all others, sooner or later die, and their shells and +hard parts lie at the bottom; and then the fine mud which is being +constantly brought down by rivers and the action of the wear and tear of +the sea, covers them over and protects them from any further change +or alteration; and, of course, as in process of time the mud becomes +hardened and solidified, the shells of these animals are preserved +and firmly imbedded in the limestone or sandstone which is being thus +formed. You may see in the galleries of the Museum up stairs specimens +of limestones in which such fossil remains of existing animals are +imbedded. There are some specimens in which turtles' eggs have been +imbedded in calcareous sand, and before the sun had hatched the young +turtles, they became covered over with calcareous mud, and thus have +been preserved and fossilized. + +Not only does this process of imbedding and fossilization occur with +marine and other aquatic animals and plants, but it affects those land +animals and plants which are drifted away to sea, or become buried in +bogs or morasses; and the animals which have been trodden down by their +fellows and crushed in the mud at the river's bank, as the herd have +come to drink. In any of these cases, the organisms may be crushed or be +mutilated, before or after putrefaction, in such a manner that perhaps +only a part will be left in the form in which it reaches us. It is, +indeed, a most remarkable fact, that it is quite an exceptional case +to find a skeleton of any one of all the thousands of wild land animals +that we know are constantly being killed, or dying in the course of +nature: they are preyed on and devoured by other animals or die in +places where their bodies are not afterwards protected by mud. There are +other animals existing in the sea, the shells of which form exceedingly +large deposits. You are probably aware that before the attempt was made +to lay the Atlantic telegraphic cable, the Government employed vessels +in making a series of very careful observations and soundings of the +bottom of the Atlantic; and although, as we must all regret, up to the +present time that project has not succeeded, we have the satisfaction +of knowing that it yielded some most remarkable results to science. +The Atlantic Ocean had to be sounded right across, to depths of several +miles in some places, and the nature of its bottom was carefully +ascertained. Well, now, a space of about 1,000 miles wide from east to +west, and I do not exactly know how many from north to south, but at +any rate 600 or 700 miles, was carefully examined, and it was found that +over the whole of that immense area an excessively fine chalky mud is +being deposited; and this deposit is entirely made up of animals whose +hard parts are deposited in this part of the ocean, and are doubtless +gradually acquiring solidity and becoming metamorphosed into a chalky +limestone. Thus, you see, it is quite possible in this way to preserve +unmistakable records of animal and vegetable life. Whenever the +sea-bottom, by some of those undulations of the earth's crust that I +have referred to, becomes upheaved, and sections or borings are made, +or pits are dug, then we become able to examine the contents and +constituents of these ancient sea-bottoms, and find out what manner of +animals lived at that period. + +Now it is a very important consideration in its bearing on the +completeness of the record, to inquire how far the remains contained +in these fossiliferous limestones are able to convey anything like an +accurate or complete account of the animals which were in existence +at the time of its formation. Upon that point we can form a very clear +judgment, and one in which there is no possible room for any mistake. +There are of course a great number of animals--such as jelly-fishes, +and other animals--without any hard parts, of which we cannot reasonably +expect to find any traces whatever: there is nothing of them to +preserve. Within a very short time, you will have noticed, after they +are removed from the water, they dry up to a mere nothing; certainly +they are not of a nature to leave any very visible traces of their +existence on such bodies as chalk or mud. Then again, look at land +animals; it is, as I have said, a very uncommon thing to find a land +animal entire after death. Insects and other carnivorous animals very +speedily pull them to pieces, putrefaction takes place, and so, out of +the hundreds of thousands that are known to die every year, it is the +rarest thing in the world to see one imbedded in such a way that its +remains would be preserved for a lengthened period. Not only is this the +case, but even when animal remains have been safely imbedded, certain +natural agents may wholly destroy and remove them. + +Almost all the hard parts of animals--the bones and so on--are composed +chiefly of phosphate of lime and carbonate of lime. Some years ago, I +had to make an inquiry into the nature of some very curious fossils +sent to me from the North of Scotland. Fossils are usually hard bony +structures that have become imbedded in the way I have described, and +have gradually acquired the nature and solidity of the body with which +they are associated; but in this case I had a series of 'holes' in some +pieces of rock, and nothing else. Those holes, however, had a certain +definite shape about them, and when I got a skilful workman to make +castings of the interior of these holes, I found that they were the +impressions of the joints of a backbone and of the armour of a great +reptile, twelve or more feet long. This great beast had died and got +buried in the sand; the sand had gradually hardened over the bones, but +remained porous. Water had trickled through it, and that water being +probably charged with a superfluity of carbonic acid, had dissolved all +the phosphate and carbonate of lime, and the bones themselves had thus +decayed and entirely disappeared; but as the sandstone happened to have +consolidated by that time, the precise shape of the bones was retained. +If that sandstone had remained soft a little longer, we should have +known nothing whatsoever of the existence of the reptile whose bones it +had encased. + +How certain it is that a vast number of animals which have existed +at one period on this earth have entirely perished, and left no trace +whatever of their forms, may be proved to you by other considerations. +There are large tracts of sandstone in various parts of the world, in +which nobody has yet found anything but footsteps. Not a bone of any +description, but an enormous number of traces of footsteps. There is no +question about them. There is a whole valley in Connecticut covered with +these footsteps, and not a single fragment of the animals which made +them has yet been found. Let me mention another case while upon that +matter, which is even more surprising than those to which I have yet +referred. There is a limestone formation near Oxford, at a place called +Stonesfield, which has yielded the remains of certain very interesting +mammalian animals, and up to this time, if I recollect rightly, there +have been found seven specimens of its lower jaws, and not a bit of +anything else, neither limb-bones nor skull, or any part whatever; not +a fragment of the whole system! Of course, it would be preposterous +to imagine that the beasts had nothing else but a lower jaw! +The probability is, as Dr. Buckland showed, as the result of his +observations on dead dogs in the river Thames, that the lower jaw, not +being secured by very firm ligaments to the bones of the head, and being +a weighty affair, would easily be knocked off, or might drop away from +the body as it floated in water in a state of decomposition. The jaw +would thus be deposited immediately, while the rest of the body would +float and drift away altogether, ultimately reaching the sea, and +perhaps becoming destroyed. The jaw becomes covered up and preserved +in the river silt, and thus it comes that we have such a curious +circumstance as that of the lower jaws in the Stonesfield slates. So +that, you see, faulty as these layers of stone in the earth's crust +are, defective as they necessarily are as a record, the account of +contemporaneous vital phenomena presented by them is, by the necessity +of the case, infinitely more defective and fragmentary. + +It was necessary that I should put all this very strongly before you, +because, otherwise, you might have been led to think differently of the +completeness of our knowledge by the next facts I shall state to you. + +The researches of the last three-quarters of a century have, in truth, +revealed a wonderful richness of organic life in those rocks. Certainly +not fewer than thirty or forty thousand different species of fossils +have been discovered. You have no more ground for doubting that these +creatures really lived and died at or near the places in which we find +them than you have for like scepticism about a shell on the sea-shore. +The evidence is as good in the one case as in the other. + +Our next business is to look at the general character of these fossil +remains, and it is a subject which it will be requisite to consider +carefully; and the first point for us is to examine how much the +extinct 'Flora' and 'Fauna' as a 'whole'--disregarding altogether +the 'succession' of their constituents, of which I shall speak +afterwards--differ from the 'Flora' and 'Fauna' of the present day;--how +far they differ in what we 'do' know about them, leaving altogether out +of consideration speculations based upon what we 'do not' know. + +I strongly imagine that if it were not for the peculiar appearance that +fossilised animals have, any of you might readily walk through a museum +which contains fossil remains mixed up with those of the present forms +of life, and I doubt very much whether your uninstructed eyes would +lead you to see any vast or wonderful difference between the two. If +you looked closely, you would notice, in the first place, a great many +things very like animals with which you are acquainted now: you would +see differences of shape and proportion, but on the whole a close +similarity. + +I explained what I meant by ORDERS the other day, when I described the +animal kingdom as being divided in sub-kingdoms, classes and orders. If +you divide the animal kingdom into orders, you will find that there are +about one hundred and twenty. The number may vary on one side or the +other, but this is a fair estimate. That is the sum total of the orders +of all the animals which we know now, and which have been known in past +times, and left remains behind. + +Now, how many of those are absolutely extinct? That is to say, how many +of these orders of animals have lived at a former period of the world's +history, but have at present no representatives? That is the sense in +which I meant to use the word "extinct." I mean that those animals did +live on this earth at one time, but have left no one of their kind +with us at the present moment. So that estimating the number of extinct +animals is a sort of way of comparing the past creation as a whole with +the present as a whole. Among the mammalia and birds there are none +extinct; but when we come to the reptiles there is a most wonderful +thing: out of the eight orders, or thereabouts, which you can make among +reptiles, one-half are extinct. These diagrams of the plesiosaurus, +the ichthyosaurus, the pterodactyle, give you a notion of some of these +extinct reptiles. And here is a cast of the pterodactyle and bones of +the ichthyosaurus and the plesiosaurus, just as fresh as if it had been +recently dug up in a churchyard. Thus, in the reptile class, there are +no less than half of the orders which are absolutely extinct. If we turn +to the 'Amphibia', there was one extinct order, the Labyrinthodonts, +typified by the large salamander-like beast shown in this diagram. + +No order of fishes is known to be extinct. Every fish that we find in +the strata--to which I have been referring--can be identified and placed +in one of the orders which exist at the present day. There is not known +to be a single ordinal form of insect extinct. There are only two orders +extinct among the 'Crustacea'. There is not known to be an extinct order +of these creatures, the parasitic and other worms; but there are +two, not to say three, absolutely extinct orders of this class, the +'Echinodermata'; out of all the orders of the 'Coelenterata' and +'Protozoa' only one, the Rugose Corals. + +So that, you see, out of somewhere about 120 orders of animals, taking +them altogether, you will not, at the outside estimate, find above ten +or a dozen extinct. Summing up all the orders of animals which have left +remains behind them, you will not find above ten or a dozen which cannot +be arranged with those of the present day; that is to say, that the +difference does not amount to much more than ten per cent.: and the +proportion of extinct orders of plants is still smaller. I think that +that is a very astounding, a most astonishing fact, seeing the enormous +epochs of time which have elapsed during the constitution of the surface +of the earth as it at present exists; it is, indeed, a most astounding +thing that the proportion of extinct ordinal types should be so +exceedingly small. + +But now, there is another point of view in which we must look at this +past creation. Suppose that we were to sink a vertical pit through the +floor beneath us, and that I could succeed in making a section right +through in the direction of New Zealand, I should find in each of the +different beds through which I passed the remains of animals which I +should find in that stratum and not in the others. First, I should come +upon beds of gravel or drift containing the bones of large animals, such +as the elephant, rhinoceros, and cave tiger. Rather curious things to +fall across in Piccadilly! If I should dig lower still, I should come +upon a bed of what we call the London clay, and in this, as you will see +in our galleries upstairs, are found remains of strange cattle, remains +of turtles, palms, and large tropical fruits; with shell-fish such as +you see the like of now only in tropical regions. If I went below +that, I should come upon the chalk, and there I should find something +altogether different, the remains of ichthyosauri and pterodactyles, and +ammonites, and so forth. + +I do not know what Mr. Godwin Austin would say comes next, but probably +rocks containing more ammonites, and more ichthyosauri and plesiosauri, +with a vast number of other things; and under that I should meet with +yet older rocks, containing numbers of strange shells and fishes; and in +thus passing from the surface to the lowest depths of the earth's crust, +the forms of animal life and vegetable life which I should meet with +in the successive beds would, looking at them broadly, be the more +different the further that I went down. Or, in other words, inasmuch +as we started with the clear principle, that in a series of +naturally-disposed mud beds the lowest are the oldest, we should come +to this result, that the further we go back in time the more difference +exists between the animal and vegetable life of an epoch and that which +now exists. That was the conclusion to which I wished to bring you at +the end of this Lecture. + + + + + +End of the Project Gutenberg EBook of The Past Condition of Organic Nature, by +Thomas H. Huxley + +*** END OF THIS PROJECT GUTENBERG EBOOK CONDITION OF ORGANIC NATURE *** + +***** This file should be named 2922.txt or 2922.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/2/9/2/2922/ + +Produced by Amy E. 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