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very large and was very deep-seated at We now turn to the changes that have the period of cooling, so that it cooled taken place in the organic beings that slowly and gave off heat for a long time lived upon the globe. This is a subject into the surrounding rocks, these are found that can only be adequately understood to be still more completely changed, having by persons acquainted with botany and acquired a different mineral structure zoology; but we will endeavour to give from what they had when first deposited an idea of the results arrived at. We as aqueous rocks, and different from what must commence by laying down a few any purely aqueons or igneous rocks pos- postulates :- 1. A species is a kind of ani

Granite, for instance, is often found mal or plant, so distinct from all others to be margined by rocks known as Gneiss that the continuation of the species is only or Mica schist, that have a schistose or possible between a pair belonging to that foliated as well as a more or less crystalline species. Offspring cannot be produced structure, and contain minerals such as by a pair of individuals of different species could have been formed only by the agency except when those species are very nearly of heat. We also find these rocks over allied, and then the progeny is barren large spaces where there is no truly either in the first or, at the farthest, in the igneous rock apparent, or not enough of it second generation. It seems to result to be adequate to the widely-spread effect. from this that all the individuals of species They always occur, too, in such situations are the descendants of a single pair.* as to allow of the supposition that they 2. Vegetable life subsists upon inorganwere deeply buried in the earth at some ic food,-matters that may be found in time after their formation, so as to have in the earth, the water, or the air, indecome within the influence of the heated pendently of animal life,-while animal interior. This would be the case if the life subsists entirely upon organic food, area on which they were originally deposit- either of vegetable or animal origin. It ed at the sea bottom became subsequently would follow that no phytophagous animal an area of depression, and if, being thickly could continue to live unless vegetable life covered with other rocks deposited above already existed in sufficient abundance to them, the depression continued long serve as its food; and no zoophagous enough for them to reach a low and there animal conld exist until there was already fore very hot level in the earth's crust. an abundance of phytophagous animals. After this we must suppose them to have The order of existence, therefore, of oragain taken their turn as areas of eleva- ganic beings must be-1st, plants; 2nd, tion, the rocks to have been lifted up plant-eating animals; 3rd, animal-eating above the sea, and their covering stripped animals. off during the process, in the way we 3. Every species of plant and animal have described. These altered rocks are has a constitution suited to the degree of termed Metamorphic or Transformed heat and light, dryness and moisture, altiRocks.

tude or depth, density of air or water, by Such have been the agencies at work which it is surrounded. It is also speciduring all the periods of our chronological ally adapted to consume certain kinds of scheme. There were always dry lands food, which are those most conducive that were being worn down, always aque- to its well-being. Let us speak of all ous rocks being formed beneath the seas these circumstances, food included, as its and lakes, always igneous rocks being in- climate. Different species are differently truded into the crust of the globe or affected by climate; some bardy kinds vomited forth upon its surface, always being able to flourish through considerable rocks that were in process of alteration in variations of it, and therefore to spread consequence of their coming within reach

over large areas : others, more delicate, of the heated interior, and the coating of being injuriously affected by the slightest the earth was always being raised in some modification of it, and therefore confined parts and depressed in others, and some- to small areas, where the peculiar conditimes fractured and convulsed, in conse- tions proper to them are alone to be found, quence of the reaction of the molten inte and where, if the conditions change, the rior upon the consolidated rind. All these species declines and perishes. operations are still going on, and we have 4. Species have come into existence, no reason to suppose that either their nature or their intensity was ever, since the commencement of the Palæozoic epoch, united in one individual, as in some of the lower

* In the case of species in which the sexes are materially different from what they are at orders of animal life, a single individual may of present.

course have sufficed instead of a pair. v0L. CVI.

6

here and there all over the globe, at difference in the date of their creation, points which we may call their centres, in, and involves the idea of great lapse of time such a way as to show that similarity of and a great succession of events as necesclimate by no means involves identity of sary to the production of the existing state species; similar climates in different parts of things. All the recent discoveries go of the globe being occupied by different, to prove that the present laws of distrithough often analogous or representative, bution in the species of animals and plants species, while in many cases, especially are the same that have reigned through when the regions are far apart, the species every known geological period. In other and even the genera are entirely distinct. words, there were always some species so Each species has spread from its centre widely diffused as to have been nearly, if over an area which is measured by its cli- not quite, cosmopolitan; and some so matic constitution.

narrowly restricted as to have been found 5. Species of animals and plants may only over very narrow areas; always some becoine extinct, either from injurious species just come into existence and strugalterations in climate,' from epidemic gling for a footing in the world; some at diseases, or from their area becoming the acme of their power and the full exinvaded by rivals powerful enough to ex- tent of their dominions, which every subterminate them, or to consume the food sequent change tended to break up and on which they previously lived. There diminish; some long past that point, and may be other causes, but these are all fading away in one, two, or more ever-lesthat we know sufficiently to be warranted sening areas; some just on the eve of in assuming them to be effective.

dying out in their last citadel of retreat. With these postulates established, Neither does there appear to be any good coupled with the circumstance that every grounds for supposing that the rate of the area that has been yet examined has extinction of old species, or that of the passed more than once through the alter creation of new, was ever materially difnations of deep sea, shallow sea, low dry ferent at one period from its rate at any land, high dry land and back again, we other. * In the absence of all proof to the perceive that the plants and animals that contrary, it seems most philosophical to lived upon it must have perished either suppose that species always died out just directly by the physical changes being as slowly and imperceptibly as they do destructive to them, or indirectly by being now. If we assume the present rate of fatal to their food, or by laying them open physical change to be the mean rate, and to the incursion of a hostile tribe who if physical change be the great modifying either ate up their food or themselves. The cause in producing changes in species by alternations in the earth's surface have that gradual destruction of the old, and been so widely spread that all the delicate that rendering necessary the creation of species of any early period must long ago have ceased to exist, even if any of the * The observed facts of geology in some instances hardy ones could have survived. The seem to warrant the notion of sudden extinction fact that all the biological provinces of the of whole races of animals or plants

, and the sud

den introduction of new assemblages of species. globe are now crowded, not only with We do not intend to deny that many of the fossils hardy species, which have a great vertical found in rocks have perished suddenly, so far as range within the province, and spread the individuals or the groups of individuals aetuperhaps through two or more provinces, iend that the notion of the sudden destruction of but also with numerous delicate and

whole species is

no case proved, and that the locally-restricted species, specially fitted arguments brought forward to prove it are entirely to peculiarities of climate, proves that fallacious. The doctrine rests upon the supposition these latter must either have come into that successive beds of rocks were deposited with existence subsequently to the development of instances this assumption is quite unsupported;

but short intervals between them. In the majority of that local climate' for which they are in many it can be shown to be entirely erroneous, adapted, or must be the last survivors of and that beds, even those to be seen in a single a race once more widely disseminated quarry, were formed with indefinitely long interwhen the climate spread over a larger vals between them ; while, in other instances, the area. In the first case, they must be of Our series is in fact but a series of fragments, each,

deposition has been rapid and almost continuous, more recent creation than many of their perhaps, representing a few years in itself, but the fellow creatures; and in the second, they intervals between them being utterly unknown. must be much older than iany.

If we found a Roman pavement just underneath a The very variety, then, in the life of modern floor, should we be warranted in supposing new, in order to keep up the completeness preceding period survived into the earlier in the life of the globe which seems to be portion of this, and a few into its latter the will of the Creator, we have the two portion. On the other hand, not only are kinds of change so linked together that many species to be found only in the rocks the rate of the one gives us the rate of of the Lower Silurian period, but some the other, and the amount of the one whole genera-especially genera of Trilogives us the measure of the other. bites and Cystidea--seem entirely to have

that the one was the immediate successor of the the globe, and the vast difference that ex

other, because there were no other pavements ists in the distribution of species, proves a between them?

Keeping these principles in mind, let us perished before the more recent Silurian now glance over the following summary period commenced, while other species, of the history of life through the fourteen forminy new genera, were now first cregeological periods specified in our table. ated to occupy their place. All the donble

Graptolites had also died out, though a Primary or Palæozoic Epoch. few single ones survived to the close of 1. Cambrian.-In the rocks of the this period, when the whole class became

extinct. Cambrian period no other distinct and in therefore belonging to the close of the era,

In the uppermost rocks, and dubitable traces of life have yet been there have been found the remains of found than the impressions of a zoophyte about a dozen species of fish, and new and the tracks of sea-worms.

2. Lower or (Cambro-) Silurian Period. forms of crustacea make their appearance, - In the rocks deposited during this

more like our present lobsters in external period the remains of animals are often of difference in structure.

shape, though having many essential points

Some of them abundant. They consist of the hard parts appear to have been six or eight feet in of Zoophytes, such as Corals, and of a

length.* class like the sea-pens (thongh perhaps of a higher organization), called Graptolites; l in some of the rocks deposited in particu

4. Devonian Period. Fishes abound a very peculiar order of Echinodermata, * called Cystidea, as well as some Stone- of strange forins, with a strong bony ar

lar areas during this period, many of them lilies and Starfish. There are several species

mour of scales that are sometimes beautiand genera of a peculiar class of bivalve

fully preserved. Several of them have shells, known as Brachiopoda,t some ordi- been graphically described, in a popular nary bivalves or Conchifera, some ordinary way, by Hugh Miller, in his ola Red anivalves or Gasteropoda, and some of a Sandstone, and their scientific description higher class belonging to the Cephalo-has been drawn up by Agassiz. In other poda. There were also many crustacean

rocks, believed to be of the same age, animals, some not very unlike our present there are an abundance of shells, corals, shrimps in external form, and a great and trilobites. A few of the species of variety of others called Trilobites, of an altogether extinct order of Crustacca. of the upper Silurian rocks, but most of

these seem to be nearly the same as those No true Fish, nor, indeed, any vertebrate the fossils differ specifically and many animal, was then in existence, if we may generically. Reptiles also existed, more judge from the negative evidence that no remains of them have yet been discovered; their remains in the beds which now form

or less nearly allied to lizards, and left neither have the relics of any land plants been as yet found in the rocks of this part of the dry land of Scotland. The

first fragments of undoubted land plants period. 3. Upper Silurian Period. The re- in Scotland and Wales, while magnificent

are found in the rocks of this period, both mains of animals are more abundant in the fronds of ferns and other plants, together rocks of this period than in that of the with a large shell like a freshwater mussel preceding, belonging generally to the same i (or Anodon), have been discovered in the classes, the same orders, and many of them to the same genera. Some even of the Upper Old red sandstone of the county of species that lived in the latter part of the

Kilkenny.

5. Curboniferous Period.-Plants were

deposited in such abundance in the rocks *Our star-fish and sea-urchins belong to the of this period as to form great beds of Echinodermata. + The Brachiopodous class of bivalves are rather in extent, and occurring at intervals

coal, spreading over many square miles lower in organisation than the Conchifera, to which our oysters and cockles belong. The Conchifera through a series of sandstones and shales, are most numerous now, though we still have a few which amount, in some places, to a total species of Brachiopoda living, some of which are supposed to belong to the same genera as those of the more numerous tribes of the earlier ages of the

Siluria, p. 264, etc. world.

+ Siluria, pp. 289, 568.

thickness of at least 8000 feet. In other and some of different genera from any of beds, especially in the limestones, the those in the rocks below, are locally abunabundance of marine shells of all kinds dant. In the sandstones of this era we (Brachiopoda, Conchifera, Gasteropoda, have the tracks of a huge frog-like animal and Cephalopoda) is quite inconceivable and other reptilian footsteps preserved. to those who have not seen them. Min- With the Permian Period we bring to gled with the remains of Stone-lilies and a close the first great epoch of our history other Echinodermata, and of corals both - that known as the Palæozoic. The reasolid and branching, they make up bed son for drawing a line of division here is after bed of solid rock, piled one upon the that there occurred about this time a vast other to such a thickness as sometimes to interval, during which the part of the form whole mountain masses many hun world now occupied by Western Europe dred feet in height. Both plants and ani- (whence our data are chiefly derived) mals belong to many different species and seems to have been more than usually genera, and the animals especially to many affected by forces of disturbance and dedifferent orders and classes, from reptiles struction. The rocks previously deposited and fish down to corals and sponges. I were greatly dislocated and tilted in variScarcely is there a single species that bas ous directions, and large parts of them reever been found in any Silurian rock, very moved by denudation, while the contemfew in any undoubted Devonian forma poraneous depositions that, doubtless, took tion. A genus of Brachiopodous livalves, place in other regions are as yet but imcalled Producta, that makes its first ap- perfectly known. Hence it results that pearance in the Devonian period, become there is in our area both a physical break, very abundant in the Carboniterous. and discordance in position, between the There are many species, some of them rocks of the Palæozoic and those of subsevery multitudinous, insomuch that the quent periods, as well as a great, and aprocks are often called Producta lime. parently a sudden, change in the organic stones.* Among the crustacea, the order remains that they respectively contain. It of Trilobites, so numerous and varied dur- does not follow that the changes may not ing the preceding epochs, is now repre- in reality have been as gradual at this as sented by a few species only, that can be at any other part of the world's history, grouped into but one or two genera. This since the seeming abruptness may be the type of animal was fading away, and with result merely of the juxtaposition of two the close of this period it becomes alto- sets of things, the dates of which were gether extinct.

widely separated in time without any sub6. Permian Period.- Another change stantial record of the interval that elapsed has now taken place-an almost entire between them. change in the species-although many of them are sufficiently near to their prede

Secondary or Mesozoic Epoch. cessors to be grouped in the same genus. A conspicuous species of Producta, for in

7. The Triassic Period.-In Britain stance, abounds in some of the rocks. Though it differs from those found in the contined to fragments of fossil wood, and

our records of lite during this period are Carboniferous series so far as to reqnire a different specific name, it is yet obviously stones of huge Batrachian and other rep

a few relies of bones, and tracks on sanda Producta.f Fish of different species, uiles similar io those that are found in the

Permian rocks. In Germany, however, * Even quarrymen are struck with the abun. dance of these shells, and in some places, with a

and on both flanks of the Alps, rocks are scarcely pardonable mistake as to the form of the found crowded with the remains of marine shell, call the rock the oyster shell limestone. creatures, part of which have an essen

+ Lions, tigers, leopards, panthers, wild and do- tially peculiar character, while others are mestic cats, however unlike in size, in colour, in variety of marking, and so on, have yet evidently more allied to Palæozoic forms. Some of so much in common that we naturally group them the genera become more fully and largely together as animals of the Cat kind, differing in developed in future periods* Many of deed in species among theniselves, and yet forming these fossils are evidently fragments of but one genus (the genus • felis,' or 'cat') when compared with all other animals, such as dogs. the missing chapters of our history. wolves, bears, &c. The specific difference and

8. (olitic or Jurassic Period.— The generic resemblance with which we are familiar in British rocks of this period are the most the above example reigus throughout the animal complete type of a great geological formaand vegetable kingdoms, and is just as real and im- tion: with which we are anywhere acportant among cockles, limpets, orsters, startish, and corals, as among creatures of the highest organization.

* Lyell's Supplement, p. 25.

quainted, whether we look to the mere | also get vegetable soils with broken stools rock groups or to their fossil contents, and prostrate stems of trees preserved in and are only to be approached by the a fossil state. great Carboniterous formation of our 9. Cretaceous Period. The fact of our islands. They are divisible into five or finding land plants and land animals in the six groups, each of which can be as clearly upper oolitic rocks of Britain, shows that subdivided into two or more sub-groups. there must have been dry land somewhere Each main group has a whole assemblage in the neighbourhood during the latter of fossils, of almost all kinds, peculiar to part of that period. There is therefore itself; while each of the sub-groups has nothing very inexpected in the fact that also its smaller but still very distinct as the earliest record of the succeeding period semblage of species, which are either which we meet with in Britain, is a fossil never, or very rarely, found in any group delta of a large river-a delta as great above or below. An old Palæozoic group apparently as that of the Nile or the of corals has become extinct with all its Ganges. The beds of this delta, which in genera and species, and been succeeded some places exceed 1000 feet in thickness, by others belonging to orders that still contain fresh-water shells, drift-wood, and exist. The Brachiopodous class of bi- the bones of strange terrestrial herbivorous valves has diminished in importance to reptiles of enormous bulk, which have something more like its present propor- received the names of Iguanodon and tions, while Conchifers and Gasteropods IIyläosaurius. Such a delta, evidently have become more numerous. Cephalo- the sweepings of a large river, involves the podous chambered univalves, which in necessity of a large and perhaps a conPalæozoic times were developed in strange tinental land; nevertheless the delta is forms of Orthoceratidæ (like Nautili uncovered by accumulations of other rocks, rolled and pulled straight), and in sharply- all crowded with the remains of marine toothed Goniatites, now appeared as Am- animals, to a depth exceeding 2000 feet, monites, with their hundreds of varieties, and spreading far and wide on all sides while the intermediate genus Nautilus, over and around it. The chalk, which is commencing in the earliest ages of the the nppermost of these accumulations, is world, has continued to appear in species alone in some places 1000 feet thick. In after species down to our own time. The the marine fossils, so numerous in the upper old forms of fish had vanished, but were rocks of the Cretaceous period, there is replaced by many new kinds, the majority again a total change in species from those of which, like the most numerous tish of found in the Oolitic rocks below. There the present day, had equal-lobed tails; were Ammonites and Belemnites, and while all Palæozoic fish resembled our Terebratulæ and other shells, with common sturgeons and sharks, in having the rays generic names in both cras; but those of both lobes of the tail wholly underneath found in the Cretaceons rocks are obviously the termination of the vertebral column. different from those found in the Oolitič. The most striking fact connected with the So with the Echinodermata, so with the life of this period, however, is the amazing Fish, so with the Reptiles, so with all development of reptile forms. Thousands other classes and orders of animals and of huge Ichthyosauri breasted the ocean, plants, so far as their remains have as yet and thousands of equally huge Plesiosauri been described. At the end of the Cretalurked along its shores. The land was ceous period we once more meet with a tenanted by immense Megalosauri, and sensible gap in our series of records, and a even the air became peopled by flying corresponding change in the characters of dragons in the shape of winged lizards, organic beings, after we have passed it. with long jaws and sharp teeth, known as Here, therefore, we draw another strong Pterodactyles. Nor was even the highest boundary line and close this second book class of the animal kingdom, the Mam- of our history, and open that of the Termalia, unrepresented, since portions of the tiary or Cainozoic epoch, which includes skeleton of several Marsupial and other that of our own days. quadrupeds' (as they used to be called) Whoever examines a museum* containhave now been disinterred from rocks belonging to this period. In the Portland and Purbeck group, which is the upper

* In London we may point to the Museum o most or newest of the colitic series, we Practical Geology and that of the Geologica

Society; there are also excellent inuseums, with

fossils chronologically arranged at Cambridge, at * Lyell's Elements, p. 312, and Supplement, p. Oxford, in Bristol, Liverpool, Manchester, York,

and other large towns in England ; at Edinburgh

13.

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