Page images
PDF
EPUB

among them.

ing a pretty complete collection of organic has ever proved to be specifically identical remains arranged in chronological order, with any animal or plant now living ; cannot tail of being struck with the fol- while in the Tertiary rocks at first a few, lowing facts. When looking over the then more, then most of the fossils are Palæozoic fossils, the forms will all appear identical with living forms. so strange to him, that he will hardly be able to pronounce to which class of the

Tertiary or Cainozoic Epoch. animal kingdom some of them belong. 10. The Eocene Period.- In the rocks Even where the class is evident, as, for of this period we find extinct Crocodiles instance, with the shells, he will see that or Alligators instead of Ichthyosauri and they obviously differ from existing shells. Pterodactyles; we find, as at present, There are no oysters, or whelks, or bar- Nautili, but no Ammonites or Belemnites, nacles, or cockles, or limpets, or periwinkles still less Goniatites or Orthoceratites.

The more familiar the The fish resemble fish now living. The observer may be with our present kinds, crustacea are obviously crabs with claws the more strange the ancient specimens and crusts like our own crabs and lobsters, will appear. When he proceeds to the the shells are Cones, and Volutes, and shells of the Secondary periods, they will Venuses, like those now living; and the seem much more familiar to him. He impressions of leaves are those of forest will say of one, perhaps, This is like an trees that resembled our own. Still there oyster or a Venus ; of another, This were few or none which in the opinion of resembles a Trochus; still, it he be well those most competent to decide were acquainted with recent shells, he will not exactly the same as any living species ; till be able to discover a single specimen to at length, as we ascended in the series of which he can assign not only a generic but European Eocene rocks, first one shell and a specific name. He will not be able to then another was found, which seemed say, “This is snch and such a Venus or actually of the same species as those that Trochus, of the same species as one that I still live. Some of the beds contain marine have in my cabinet of recent shells at remains only, others have them mingled home, When, however, he comes to the with those of freshwater animals, and in fossils got from Tertiary rocks, it is no others again the latter alone are found longer the difference between the fossil without

any

admixture of marine and the living forms that will strike him, creatures. Together with the remains of but their resemblance, and in some cases freshwater animals, we get those of animals their identity. The curious old puzzling that lived upon the land—some of them forms have all disappeared; almost every large mammalia, like tapirs, or interspecies belongs to a still existing genus, or mediate between tapirs and rhinoceroses is very closely allied to it; oysters, whelks, and other thick-skinned or ruminant quaand barnacles, cochles, limpets, and peri- drupeds, often filling up apparent gaps in winkles, and the numerous other kinds for the existing creation, and completing by a which our language (more barren in names number of otherwise missing links the for natural objects than many savage chain of gradation in animal life. Abuntongues) has no distinctive appellation, dance of palm-like fruits, and seeds like now appear in abundance and in many coffee and other berries, are preserved in varieties. We have in these facts the some of these deposits. most obvious expression of a great law- 11. The Miocene Period.—The proporthat, namely, of the gradual approximation tion of existing to extinct species of shells to existing forms, and the gradual appear- becomes higher in the deposits of this ance of existing species: the first may be period. Among the remains are the bones traced throughout the series of life from of large animals, one of which seems to the earliest to the latest times; the last, have been like a great water elephant with which is its necessary conclusion, is only down-curved tusks, proceeding from the apparent in the Tertiary epoch. Among lower jaw instead of the upper. It is the hundreds and thousands of species of called å Dinotherium from its bulk. animals and plants discovered in the 12. The Pliocene Period.The number Palzeozoic and Mesozoic rocks, not one of existing species of shells is in these

deposits even greater than that of the in Scotland (we cannot answer for Glasgow, Aber- extinct; while in deen, or St. Andrews); while in Ireland they are 13. The Pleistocene Period the absoto be seen in the Museum of Irish Industry, and lutely extinct species of Mollusca become of such collectious in the Queen's Colleges of the exception, the great majority either Belfast, Cork, and Galway.

living in the seas surrounding the lands, in the rocks of which they are found fossil, in the more recent Tertiary deposits of or in some neighbouring waters.

Australia South America is now the 14. The Modern or Human Period is only country in which sloths and armadilthus gradually introduced, when apparent- los are found. Great extinct animals, ly all existing species of animals and plants allied to sloths and armadillos, known as were already living, and man at length Megatherium, Mylodon, and Glyptodon, was placed upon the

stage prepared for him. have been found in the recent Tertiary During these Tertiary periods our atten- rocks of South America. New Zealand, tion is naturally attracted from the study the country of the singular wingless bird of the remains of the lower classes of called Apteryx, contains the bones of the animals to that of the higher class Mam- gigantic wingless Dinornis. The true malia, to which we ourselves belong. swine (Sus) are now confined to the Old Mammalian animals are abundant in the World ; the peccary (Dicotyles) to the rocks of all the Tertiary periods. Those New; no fossil species of hög has been in the earliest or Eocene period are so found in the New, nor of peccary in the different from any now existing, that new Old. The rhinoceros, a genus now congeneric names had to be invented for fined to the Old World, where several almost all of them. One kind of animal, extinct species of it have often been found of which eleven or twelve species were fossil, has never been found fossil in found, some as large as a rhinoceros, America. Monkeys have been found fosothers varying in size from that of a horse sil in the tertiary deposits of both the Old to that of a hog,' had in its skeleton some World and the New, but those found in of the characteristics of the tapir, others the Old belong to the Catarhine division like those of the rhinoceros, others like of monkeys, and those in the New to the those of a horse. It was called a Palæo- Platyrhine—such division being now retherium. Another genus, christened Ano- stricted as formerly to the respective conplotherium, of which five species have tinents.* been found, was in one respect inter- We have evidence that in the Pleistocene mediate between the rhinoceros and the period (that which immediately preceded horse, and in another between the bippo- our own) the temperate parts of the northpotamus, the bog, and the camel.* ern hemisphere experienced a peculiar

More than twenty genera have been change of climate; large parts of Europe, formed to include various species of Asia, and North America being depressed animals, and seventeen of these bave never beneath the sea, and the mountains (then been found in any deposits more recent islands) being covered with glaciers, while then the Eocene. Others survived into the their coasts were surrounded by icefloes Miocene period, and became the contem- and icebergs. The severe climate continued poraries of new genera, of which we have after these lands were lifted up again, and already mentioned one, the Dinotherium, connected by plains still more extensive than but there were many others, as the strange the present. During this Glacial Period, Sivatherium with its four horns; and with as it is sometimes called, a woolly elephant these there were extinct species belonging (Elephas primigenius, or Mammoth), and a to genera which still exist, such as the woolly rhinoceros (Rh.tichorhinus) roamed hippopotamus and rhinoceros, deer and over the plains from Siberia to Britain, giraffe ; together with numerous kinds of and their remains are now found more or elephantine animals, some of them allied to less intimately associated with those of the two existing elephants, others varying lions, bears, hyænas, Irish elks, and other so much as to require the generic name of forms, most of which died out before the Mastodon. Different species of these, creation of man, while others survived to and of many other existing genera, as well be his contemporaries, and were, perhaps, as species of genera now extinct, came into finally exterminated by him. Many shells, existence in various parts of the world now inhabitants of Arctic seas, ranged during the Miocene and subsequent into our latitudes during this glacial peperiods, so as to introduce, as it were, in riod; while others, that had previously each large division of the globe the present inhabited British seas, retreated southpeculiarities of mammalian life. Austral- wards to Mediterranean shores, but have asia is now the exclusive home of kangeroos again spread northwards as the cold cliand wombats, and all other Marsupials, mate receded towards its present limits. except the Didelphys. Large fossil kan- In this rapid sketch we have not related garoos and wombats, &c., have been found Owen's Notes to the 8rd Edition of the

* Owen's Address to the British Association at

Leeds. * Bridgewater Treatise.'

a thousandth part of what is to be told first large chamber of a coiled many-chamof the ancient history of the earth and bered shell

, all the chambers being traits inhabitants. In Britain alone more versed by a tube proceeding down the extinct species of mammalia have been centre of the shell. This simply-formed found than there are species of mammalia shell existed at a very early period. Shells now living in our islands. Ten times as differing from Nautilus only in some modi. many extinct reptiles, five times as many fication in the coiling of the shell, whence extinct fish, seven times as many extinct they receive the name of Lituites (or trumechinodermata, nine times as many extinct pet-shell), existed in the Cambro-Silurian, shell-bearing molluscs, and six times as others in the Silurian period. True Naumany extinct zoophytes, have been found tili make their appearance in the rocks of in British rocks, as now exist in British the Devonian and Carboniferous periods; waters or on British lands. Nor is this and ever since there seems to have been all. The eager search of naturalists must one or two species of shell in existence, have nearly exhausted the discoveries to which, however they may have differed be made among the surviving species of among themselves in shape, size, or prothose animals that inhabit our particular portion of parts, yet agreed in the essenregion of the earth; whereas new species tial characters of a Nautilus. During the are daily being exhumed from the rocks, whole Palæozoic epoch there was another and future research will greatly angment very remarkable form of the order, which their number. Even did we know the was like a Nautilus unrolled and pulled fossil species to be found in Britain as com- out into a straight, conical, horn-like shell, pletely as we know its living fauna, we called an Orthoceras (or straight horn). cannot suppose that those fossil species As in the Nautilus, so in the Orthoceras, are all that ever lived in our area. Hun- the septa or divisions of the chambers were dreds may have perished and left no re- plain, like saucers, and the siphuncle or mains.

internal tube was central. Different groups Volumes might be written, not merely of species of these shells appeared at differon the history of the contemporary assem- ent periods, some of them being strangely blages of animals belonging to the different modified into fusiform or pear-shaped outperiods, but on the history of any one class lines with diversely pinched-up mouths, of animals

, tracing its progress, and the and with many variations in the structure changes introduced into it as it passed from of the siphuncle. In the Carboniferous one period to another. We are tempted period one or two very large species, of to give, as an example, a sketch of the which the shells were at least as big as a chambered-univalve shells, belonging to man's leg, made their appearance; and the class Cephalopoda, or that class of shortly afterwards the whole family of Orwhich the cuttlefish is a member.

thoceratidæ died out and became extinct. The class Cephalopoda is divided into

ito In the meantime one or two other genera two great orders,— 1st. The Dibranchiata, or families of coiled chambered shells had or those having two branchiæ; 2nd. The come into existence, as the Clymenia, of Tetrabranchiata, or those having four | which the siphuncle was on the internal branchiæ. The first order includes the margin, while the septa of the chambers common cuttlefishes, which are divided were either simple or sinuous; and the into two groups,

-a, those with eight Gyroceras, of which the septa were simple, arms, of which the Poulpes and the Argo- but the siphuncle was on the external marnant are examples; b, those with ten arms, gin; and, lastly, the Goniatites, of which of which the Squids are examples. Some the siphucle was on or near the external of these latter, as the Sepia and Loligo, margin, but the septa of the chambers have internal hard supports, popularly were deeply indented by very acute, toothcalled “bones ;' others, as the Spirula, have like folds, both on the sides and the back chambered shells more or less internal; and of the shell, the edges of the saucer-like there formerly existed in the Secondary divisions being pinched into Vandyke epoch only) a family called Belemnites, in fills. which the internal so-called “bone' was Soon after the commencement of the curiously modified into a conical . form great Secondary epoch all these forms, with an internal chambered conical com- with their many species and varieties, had partment, from which proceeded a na disappeared (except the Nautilus); but creous sheath inclosing the ink-bag. now commenced a new set of variations

The second order, or Tetrabranchiata, is on the same great theme. The sharprepresented by but one living animal-toothed folds in the septa of the Goniatite namely, the Nautilus, which inhabits the were first modified into bold and regular semicircular curves, each alternate curve, | internal septa and dorsal siphuncles was as it waved from the mouth of the shell, on the point of being laid aside for ever. being notched by several little short cuts, In the Ammonitidæ the varieties seem to while the curve that waved towards the have been prodigally introduced, and the mouth of the shell was left plain. This whole type rapidly exhausted, as if it were form, which lived in the Triassic period, is desirable for some reason to get rid of it, called a Ceratites, and it introduces gradu. but it was intended first to show of what ally the great genus Ammonites of the a multitude of adaptations it was capable. two more recent periods. In the Ammo- In the Tertiary epoch, and down to the nites the siphuncle still remains on the present day, we find only the Nautilus,back of the shell, which retains its regu- one indeed in the Eocene period having larly coiled, discoidal form: while every zig-zag divisions in the chambers, but the imaginable variation takes place in the others remarkable, like the present Naucurvature, indentation, corrugation, and tilus, chiefly for their simple structure, ramification of the septa of the chambers, their graceful outline, and the nacreous which produce sometimes the most intri- lustre of the inner portion of the shell. cate leaf-like patterns on the sides of the A similar strange, eventful history' shell. Equal variations occur in the shape might be told for other classes of the aniand size of the shell itself; some being mal kingdom, of which the data are to be nearly globular, others almost as flat as procured with greater or less completepancakes, with a sharp edge like a quoit; ness, and probably might be told for every some being no bigger than a shilling, class of animal and plant, if the entire reothers as large as a cart-wheel. Nearly cords of their history could be recovered. six hundred different species of Ammonites Truly may it be said that there are more are known, all of which have been found sermons in stones' than Shakspeare ever in rocks belonging to the Secondary epoch, thought of; and that, whether in their and in those only. Besides this immense native beds or when ticketed and arranged development of species in the genus Am- on the shelves of a museum, they tell a monite, there are found additional modifi- story which, if it be once listened to, speaks cations in the external form of the shells, to the mind of inan in terms that cannot which become so great as to compel us to fail to awaken the highest interest. This give them other generic names. In one wonderful biological law of the succession of these tbe coils of the shell are slightly of species, and the gradual modification separated, so as not to touch each other, – of the types of living forms in progressive this is called Crioceras; in another the ages, is not only a remarkable scientific shell is partially unrolled, and then turned fact, but has a direct economical value up at the end, so as to assume a boat-like when applied to practical purposes. form, whence it is called a Scaphites; in a It has happened that particular subthird, called a Hamites, one part of the stances of great value to man, such as shell is straight, and the other bent up rock-salt or coal, have been deposited over like a hook; while in a fourth, known as certain areas. Let us select coal as an exa Baculites, the whole shell becomes as ample. Coal has been formed during straight as a stick. In external form this many, and might have been formed during latter resembles an Orthoceras; but as it any geological period. There was one, has its internal septa convoluted and cor- however, in which its formation rugated, it is evident that it bears the same unusually frequent, and took place over relation to an Ammonite that the Ortho-many areas of the earth's surface, that ceras does to the Nautilus. Another form, period being hence called the Carboniferous again, is called Turrilites, being like an period. In Britain and Western Europe, Ammonite internally, but having an exter- although coal does oécur in the rocks of dal form more like a whelk, as it some one other periods, yet it is in those of the Carhad taken the centre of a flat Ammonite boniferous only that it has ever been and pulled it up till the shell became a found in sufficient abundance and of suftitower instead of a disc. There are several ciently good quality to be of any great intermediate forms between those now value. It would not therefore be worth mentioned, and it is very remarkable that while to go to any expense in the search all these strange and rapid variations in after coal, unless in rocks of the Carbonithe external form of the Ammoni- | ferous era. How are we to ascertain this tidæ are found chiefly in the Cretaceous cardinal fact? It is true that coal-bearing rocks, and appear, therefore, to bave been rocks generally consist pretty largely of produced just before the whole type of dark-coloured clays, grey and black shales, the cephalopodous shells with corrugated and similar deposits. But then equally

was

dark shales and clays occur in abundance an insuperable difficulty in understanding in the formations of other periods which geological classification and nomenclature. have never been found to contain any The reason of this difficulty appears to be beds of coal. Neither is there any other the double signification of many of the indication to be found in the nature of the terms used by geologists in speaking of rocks, or in that of the ground, which their stratified rock-groups, and it may be will give any trustworthy information as as well perlaps here to give an explanato the period at which those rocks were tion of it. The original name given to a deposited. When, however, the geologist formation has often been descriptive of the has worked out his series of organic re- kind of rock of which it was principally commains, and knows that, during the Carboni- | posed, or the most important mineral subferous period, such and such animals and stance it contained. Thus the Cretaceous plants existed on the globe, and those only, formation was so named, because in the he looks to the fossil fragments in the district where it was first studied a large rocks in which the exploration is being part of it consisted of chalk; the Oolitic carried on, certain that if he can discover formation contained in the typical district a specimen it will give him the information many beds of oolitic limestone, the Carhe seeks. If he find Carboniferous fossils boniferous many beds of coal. Other he knows the rocks to be of Carboniferous names had a geographical signification, age, whether they happen to contain beds such as Devonian, the formations to be seen of coal in that place or not. If, on the in Devonshire ; Silurian, those in the disother hand, the black shales contain frag-trict of Siluria. As soon, however, as ments of Graptolites or of Silurian shells, these names are once established, they corals, or trilobites, he knows that these rapidly lose their orignal import, and acare of Silurian age, and that no coal worth quire a purely chronological meaning. working has ever been found in our area When, for instance, we trace the Cam. of the world in or beneath any beds be- brian, Devonian, or Silurian rocks beyond longing to a Silurian formation. If, again, the borders of the district where they he finds fragments of Belemnites or of were first observed, it is clear that the Oolitic or Cretaceous shells, &c., he knows strictly geographic term becomes no longer that the rocks in which they lie, whether literally applicable. It is indeed somewhat they be black shale or white sandstone, of a bull to speak of Cambrian, Silurian, were deposited long after the Carboni- or Devonian rocks as existing in Ireland ferous period, and that, although the rocks or Scotland. What is meant is, that the of the Carboniferous period may possibly Cambrian rocks of Ireland or Scotland are be below him, yet that in order to reach a continuation of those of Cambria ; in them he will have to pass through not only other words, that they were deposited tothe whole of the formation in wbich he is gether with them, at the same time, in the commencing to dig, but also probably same seas, or in neighbouring seas, as the through great series of beds deposited case may be. In like manner, when we during the Permian and Triassic periods, come to trace the Cretaceous, Oolitic, or and therefore that the Carboniferous for- Carboniferous formations from one area to mation lies at too great a depth for him to another, it often happens that the nature reach it. Moreover it is quite possible of the rock gradually changes. Each for: that, even if he pierced the intervening mation consists of a vast number of sepastrata, it might happen that no Carboni- rate beds of rock, every one of which varies ferous rocks had ever been deposited in almost indefinitely in extent. The beds of that particular spot, or, having been de- coal which gave their name to the Carboniposited, had been removed by denudation ferous rocks, because of their economical before the upper · strata were formed. importance, are very few compared with Want of attention to these simple rules the whole bulk of those rocks, and somehas, within the last twenty or thirty years, times get thinner and fewer till they discaused a fruitless expenditure of many appear altogether; while the other portion hundred thousand pounds, and is even goes on and spreads perhaps over large now involving the waste of a few hundreds areas, in which we may have the apparent in one place and a few thousands in another, contradiction of Carboniferous rocks to an amount that would be almost incon- almost or entirely destitute of any carboceivable if unbounded ignorance were not naceous matter. In like manner the known by experience to be unbounded in Oolitic formations in many parts of the its credulity.

world contain no oolites, and the CretaThere are many persons desirous of ceous formations no chalk. Indeed the knowing something of geology, who find Cretaceous formations of South America

[ocr errors]
« PreviousContinue »