ing a pretty complete collection of organic remains arranged in chronological order, cannot fail of being struck with the following facts. When looking over the Paleozoic fossils, the forms will all appear so strange to him, that he will hardly be able to pronounce to which class of the animal kingdom some of them belong. Even where the class is evident, as, for instance, with the shells, he will see that they obviously differ from existing shells. There are no oysters, or whelks, or barnacles, or cockles, or limpets, or periwinkles among them. The more familiar the observer may be with our present kinds, the more strange the ancient specimens will appear. When he proceeds to the shells of the Secondary periods, they will seem much more familiar to him. He will say of one, perhaps, This is like an oyster or a Venus; of another, This resembles a Trochus; still, if he be well acquainted with recent shells, he will not be able to discover a single specimen to which he can assign not only a generic but a specific name. He will not be able to say, This is such and such a Venus or Trochus, of the same species as one that I have in my cabinet of recent shells at home.' When, however, he comes to the fossils got from Tertiary rocks, it is no longer the difference between the fossil and the living forms that will strike him, but their resemblance, and in some cases their identity. The curious old puzzling forms have all disappeared; almost every species belongs to a still existing genus, or is very closely allied to it; oysters, whelks, and barnacles, cockles, limpets, and periwinkles, and the numerous other kinds for which our language (more barren in names for natural objects than many savage tongues) has no distinctive appellation, now appear in abundance and in many varieties. We have in these facts the most obvious expression of a great lawthat, namely, of the gradual approximation to existing forms, and the gradual appearance of existing species: the first may be traced throughout the series of life from the earliest to the latest times; the last, which is its necessary conclusion, is only apparent in the Tertiary epoch. Among the hundreds and thousands of species of animals and plants discovered in the Paleozoic and Mesozoic rocks, not one has ever proved to be specifically identical with any animal or plant now living; while in the Tertiary rocks at first a few, then more, then most of the fossils are identical with living forms. In the rocks Tertiary or Cainozoic Epoch. 10. The Eocene Period. of this period we find extinct Crocodiles or Alligators instead of Ichthyosauri and Pterodactyles; we find, as at present, Nautili, but no Ammonites or Belemnites, still less Goniatites or Orthoceratites. The fish resemble fish now living. The crustacea are obviously crabs with claws and crusts like our own crabs and lobsters, the shells are Cones, and Volutes, and Venuses, like those now living; and the impressions of leaves are those of forest trees that resembled our own. Still there were few or none which in the opinion of those most competent to decide were exactly the same as any living species; till at length, as we ascended in the series of European Eocene rocks, first one shell and then another was found, which seemed actually of the same species as those that still live. Some of the beds contain marine remains only, others have them mingled with those of freshwater animals, and in others again the latter alone are found without any admixture of marine creatures. Together with the remains of freshwater animals, we get those of animals that lived upon the land-some of them large mammalia, like tapirs, or intermediate between tapirs and rhinoceroses and other thick-skinned or ruminant quadrupeds, often filling up apparent gaps in the existing creation, and completing by a number of otherwise missing links the chain of gradation in animal life. Abundance of palm-like fruits, and seeds like coffee and other berries, are preserved in some of these deposits. 11. The Miocene Period.-The proportion of existing to extinct species of shells becomes higher in the deposits of this period. Among the remains are the bones of large animals, one of which seems to have been like a great water elephant with down-curved tusks, proceeding from the lower jaw instead of the upper. It is called a Dinotherium from its bulk. 12. The Pliocene Period.-The number of existing species of shells is in these deposits even greater than that of the 13. The Pleistocene Period the abso in Scotland (we cannot answer for Glasgow, Aber-extinct; while in deen, or St. Andrews); while in Ireland they are to be seen in the Museum of Irish Industry, and that of Trinity College in Dublin, and beginnings of such collections in the Queen's Colleges of Belfast, Cork, and Galway. lutely extinct species of Mollusca become the exception, the great majority either living in the seas surrounding the lands, in the rocks of which they are found fossil, or in some neighbouring waters. 14. The Modern or Human Period is thus gradually introduced, when apparently all existing species of animals and plants were already living, and man at length was placed upon the stage prepared for him. During these Tertiary periods our attention is naturally attracted from the study of the remains of the lower classes of animals to that of the higher class Mammalia, to which we ourselves belong. Mammalian animals are abundant in the rocks of all the Tertiary periods. Those in the earliest or Eocene period are so different from any now existing, that new generic names had to be invented for almost all of them. One kind of animal, of which eleven or twelve species were found, some as large as a rhinoceros, others varying in size from that of a horse to that of a hog,' had in its skeleton some of the characteristics of the tapir, others like those of the rhinoceros, others like those of a horse. It was called a Palæotherium. Another genus, christened Anoplotherium, of which five species have been found, was in one respect intermediate between the rhinoceros and the horse, and in another between the hippopotamus, the hog, and the camel.* More than twenty genera have been formed to include various species of animals, and seventeen of these have never been found in any deposits more recent then the Eocene. Others survived into the Miocene period, and became the contemporaries of new genera, of which we have already mentioned one, the Dinotherium, but there were many others, as the strange Sivatherium with its four horns; and with these there were extinct species belonging to genera which still exist, such as the hippopotamus and rhinoceros, deer and giraffe; together with numerous kinds of elephantine animals, some of them allied to the two existing elephants, others varying so much as to require the generic name of Mastodon. Different species of these, and of many other existing genera, as well as species of genera now extinct, came into existence in various parts of the world during the Miocene and subsequent periods, so as to introduce, as it were, in each large division of the globe the present peculiarities of mammalian life. Australasia is now the exclusive home of kangeroos and wombats, and all other Marsupials, except the Didelphys. Large fossil kangaroos and wombats, &c., have been found Owen's Notes to the 3rd Edition of the Bridgewater Treatise.' in the more recent Tertiary deposits of Australia. South America is now the only country in which sloths and armadillos are found. Great extinct animals, allied to sloths and armadillos, known as Megatherium, Mylodon, and Glyptodon, have been found in the recent Tertiary rocks of South America. New Zealand, the country of the singular wingless bird called Apteryx, contains the bones of the gigantic wingless Dinornis. The true swine (Sus) are now confined to the Old World; the peccary (Dicotyles) to the New; no fossil species of hog has been found in the New, nor of peccary in the Old. The rhinoceros, a genus now confined to the Old World, where several extinct species of it have often been found fossil, has never been found fossil in America. Monkeys have been found fossil in the tertiary deposits of both the Old World and the New, but those found in the Old belong to the Catarhine division of monkeys, and those in the New to the Platyrhine-such division being now restricted as formerly to the respective continents.* We have evidence that in the Pleistocene period (that which immediately preceded our own) the temperate parts of the northern hemisphere experienced a peculiar change of climate; large parts of Europe, Asia, and North America being depressed beneath the sea, and the mountains (then islands) being covered with glaciers, while their coasts were surrounded by icefloes and icebergs. The severe climate continued after these lands were lifted up again, and connected by plains still more extensive than the present. During this Glacial Period, as it is sometimes called, a woolly elephant (Elephas primigenius, or Mammoth), and a woolly rhinoceros (Rh. tichorhinus) roamed over the plains from Siberia to Britain, and their remains are now found more or less intimately associated with those of lions, bears, hyænas, Irish elks, and other forms, most of which died out before the creation of man, while others survived to be his contemporaries, and were, perhaps, finally exterminated by him. Many shells, now inhabitants of Arctic seas, ranged into our latitudes during this glacial period; while others, that had previously inhabited British seas, retreated southwards to Mediterranean shores, but have again spread northwards as the cold climate receded towards its present limits. In this rapid sketch we have not related * Owen's Address to the British Association at Leeds. a thousandth part of what is to be told of the ancient history of the earth and its inhabitants. In Britain alone more extinct species of mammalia have been found than there are species of mammalia now living in our islands. Ten times as many extinct reptiles, five times as many extinct fish, seven times as many extinct echinodermata, nine times as many extinct shell-bearing molluses, and six times as many extinct zoophytes, have been found in British rocks, as now exist in British waters or on British lands. Nor is this all. The eager search of naturalists must have nearly exhausted the discoveries to be made among the surviving species of those animals that inhabit our particular region of the earth; whereas new species are daily being exhumed from the rocks, and future research will greatly augment their number. Even did we know the fossil species to be found in Britain as completely as we know its living fauna, we cannot suppose that those fossil species are all that ever lived in our area. Hundreds may have perished and left no remains. Volumes might be written, not merely on the history of the contemporary assemblages of animals belonging to the different periods, but on the history of any one class of animals, tracing its progress, and the changes introduced into it as it passed from one period to another. We are tempted to give, as an example, a sketch of the chambered-univalve shells, belonging to the class Cephalopoda, or that class of which the cuttlefish is a member. The class Cephalopoda is divided into two great orders,-1st. The Dibranchiata, or those having two branchiæ; 2nd. The Tetrabranchiata, or those having four branchiæ. The first order includes the common cuttlefishes, which are divided into two groups, -a, those with eight arms, of which the Poulpes and the Argonaut are examples; b, those with ten arms, of which the Squids are examples. Some of these latter, as the Sepia and Loligo, have internal hard supports, popularly called 'bones; others, as the Spirula, have chambered shells more or less internal; and there formerly existed (in the Secondary epoch only) a family called Belemnites, in which the internal so-called 'bone' was curiously modified into a conical form with an internal chambered conical compartment, from which proceeded a nacreous sheath inclosing the ink-bag. first large chamber of a coiled many-chambered shell, all the chambers being traversed by a tube proceeding down the centre of the shell. This simply-formed shell existed at a very early period. Shells differing from Nautilus only in some modification in the coiling of the shell, whence they receive the name of Lituites (or trumpet-shell), existed in the Cambro-Silurian, others in the Silurian period. True Nautili make their appearance in the rocks of the Devonian and Carboniferous periods; and ever since there seems to have been one or two species of shell in existence, which, however they may have differed among themselves in shape, size, or proportion of parts, yet agreed in the essential characters of a Nautilus. During the whole Paleozoic epoch there was another very remarkable form of the order, which was like a Nautilus unrolled and pulled out into a straight, conical, horn-like shell, called an Orthoceras (or straight horn). As in the Nautilus, so in the Orthoceras, the septa or divisions of the chambers were plain, like saucers, and the siphuncle or internal tube was central. Different groups of species of these shells appeared at different periods, some of them being strangely modified into fusiform or pear-shaped outlines with diversely pinched-up mouths, and with many variations in the structure of the siphuncle. In the Carboniferous period one or two very large species, of which the shells were at least as big as a man's leg, made their appearance; and shortly afterwards the whole family of Or thoceratidæ died out and became extinct. In the meantime one or two other genera or families of coiled chambered shells had come into existence, as the Clymenia, of which the siphuncle was on the internal margin, while the septa of the chambers were either simple or sinuous; and the Gyroceras, of which the septa were simple, but the siphuncle was on the external margin; and, lastly, the Goniatites, of which the siphuncle was on or near the external margin, but the septa of the chambers were deeply indented by very acute, toothlike folds, both on the sides and the back of the shell, the edges of the saucer-like divisions being pinched into Vandyke frills. Soon after the commencement of the great Secondary epoch all these forms, with their many species and varieties, had disappeared (except the Nautilus); but 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 on the point of being laid aside for ever. In the Ammonitidæ the varieties seem to have been prodigally introduced, and the whole type rapidly exhausted, as if it were desirable for some reason to get rid of it, but it was intended first to show of what a multitude of adaptations it was capable. In the Tertiary epoch, and down to the present day, we find only the Nautilus,one indeed in the Eocene period having zig-zag divisions in the chambers, but the others remarkable, like the present Nautilus, chiefly for their simple structure, their graceful outline, and the nacreous lustre of the inner portion of the shell. A similar strange, eventful history' might be told for other classes of the animal kingdom, of which the data are to be procured with greater or less completeness, and probably might be told for every class of animal and plant, if the entire records of their history could be recovered. Truly may it be said that there are more sermons in stones' than Shakspeare ever thought of; and that, whether in their native beds or when ticketed and arranged on the shelves of a museum, they tell a story which, if it be once listened to, speaks to the mind of man in terms that cannot fail to awaken the highest interest. This wonderful biological law of the succession of species, and the gradual modification of the types of living forms in progressive ages, is not only a remarkable scientific fact, but has a direct economical value when applied to practical purposes. semicircular curves, each alternate curve, | internal septa and dorsal siphuncles was as it waved from the mouth of the shell, being notched by several little short cuts, while the curve that waved towards the mouth of the shell was left plain. This form, which lived in the Triassic period, is called a Ceratites, and it introduces gradually the great genus Ammonites of the two more recent periods. In the Ammonites the siphuncle still remains on the back of the shell, which retains its regularly coiled, discoidal form: while every imaginable variation takes place in the curvature, indentation, corrugation, and ramification of the septa of the chambers, which produce sometimes the most intricate leaf-like patterns on the sides of the shell. Equal variations occur in the shape and size of the shell itself; some being nearly globular, others almost as flat as pancakes, with a sharp edge like a quoit; some being no bigger than a shilling, others as large as a cart-wheel. Nearly six hundred different species of Ammonites are known, all of which have been found in rocks belonging to the Secondary epoch, and in those only. Besides this immense development of species in the genus Ammonite, there are found additional modifications in the external form of the shells, which become so great as to compel us to give them other generic names. In one of these the coils of the shell are slightly separated, so as not to touch each other,this is called Crioceras; in another the shell is partially unrolled, and then turned up at the end, so as to assume a boat-like form, whence it is called a Scaphites; in a third, called a Hamites, one part of the shell is straight, and the other bent up like a hook; while in a fourth, known as a Baculites, the whole shell becomes as straight as a stick. In external form this latter resembles an Orthoceras; but as it has its internal septa convoluted and corrugated, it is evident that it bears the same relation to an Ammonite that the Orthoceras does to the Nautilus. Another form, again, is called Turrilites, being like an Ammonite internally, but having an external form more like a whelk, as if some one had taken the centre of a flat Ammonite and pulled it up till the shell became a tower instead of a disc. There are several intermediate forms between those now mentioned, and it is very remarkable that all these strange and rapid variations in the external form of the family Ammonitidæ are found chiefly in the Cretaceous rocks, and appear, therefore, to have been produced just before the whole type of the cephalopodous shells with corrugated It has happened that particular substances of great value to man, such as rock-salt or coal, have been deposited over certain areas. Let us select coal as an example. Coal has been formed during many, and might have been formed during any geological period. There was one, however, in which its formation was unusually frequent, and took place over many areas of the earth's surface, that period being hence called the Carboniferous period. In Britain and Western Europe, although coal does occur in the rocks of other periods, yet it is in those of the Carboniferous only that it has ever been found in sufficient abundance and of sufficiently good quality to be of any great value. It would not therefore be worth while to go to any expense in the search after coal, unless in rocks of the Carboniferous era. How are we to ascertain this cardinal fact? It is true that coal-bearing rocks generally consist pretty largely of dark-coloured clays, grey and black shales, and similar deposits. But then equally 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 perhaps 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 Camof 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 which 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 forthat, 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 Cretaceous formations no chalk. Indeed the Cretaceous formations of South America There are many persons desirous of knowing something of geology, who find |