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diff --git a/old/thx0210.txt b/old/thx0210.txt new file mode 100644 index 0000000..0821907 --- /dev/null +++ b/old/thx0210.txt @@ -0,0 +1,941 @@ +Project Gutenberg Etext of The Past Condition of Organic Nature +#12 in our series by Thomas H. Huxley + +Copyright laws are changing all over the world, be sure to check +the laws for your country before redistributing these files!!! + +Please take a look at the important information in this header. +We encourage you to keep this file on your own disk, keeping an +electronic path open for the next readers. + +Please do not remove this. + +This should be the first thing seen when anyone opens the book. +Do not change or edit it without written permission. 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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 yl; 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. + +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.) + +[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 Bl). 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 he +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 Etext of +The Past Condition of Organic Nature by Thomas H. Huxley + diff --git a/old/thx0210.zip b/old/thx0210.zip Binary files differnew file mode 100644 index 0000000..a37c519 --- /dev/null +++ b/old/thx0210.zip |