Tracks of a Lower Silurian reptile in Canada.—In the year 1847, Mr. Robert Abraham announced in the Montreal Gazette, of which he was editor, that the track of a freshwater tortoise had been observed on the surface of a stratum of sandstone in a quarry opened on the banks of the St. Lawrence at Beauharnais in Upper Canada. The inhabitants of the parish being perfectly familiar with the track of the amphibious mud-turtles or terrapins of their country, assured Mr. Abraham that the fossil impressions closely resembled those left by the recent species on sand or mud. Having satisfied himself of the truth of their report, he was struck with the novelty and geological interest of the phenomenon. Imagining the rock to be the lowest member of the old red sandstone, he was aware that no traces had as yet been found of a reptile in strata of such high antiquity.

He was soon informed by Mr. Logan, at that time engaged in the geological survey of Canada, that the white sandstone above Montreal was really much older than the "Old Red," or Devonian. It had in fact been ascertained many years before, by the State surveyors of New York (who called it the "Potsdam Sandstone"), to lie at the base of the whole Silurian series. As such it had been pointed out to me in 1841, in the valley of the Mohawk, by Mr. James Hall[vii-A], and its position was correctly described by Mr. Emmons, on the borders of Lake Champlain, where I examined it in 1842. It has there the character of a shallow-water deposit, ripple-marked throughout a considerable thickness, and full of a species of Lingula. The flat valves of this shell, of a dark colour, are so numerous, and so arranged in horizontal layers, as to play the part of mica, causing the rock to divide into laminÆ, as in some micaceous sandstones.

When I mentioned this rock in my Travels[vii-B] as occurring between Kingston and Montreal, (the same in which the Chelonian foot-prints have since been found,) I spoke of it as the lowest member of the Lower Silurian series; but no traces of any organic being of a higher grade than the Lingula had then been seen in it, and I called attention to the singular fact, that the oldest fossil form then known in the world, was a marine shell strictly referable to a genus now existing.

Early in the year 1851, Mr. Logan laid before the Geological Society of London a slab of this sandstone from Beauharnais, containing no less than twenty-eight foot-prints of the fore and hind feet of a quadruped, and six casts in plaster of Paris, exhibiting a continuation of the same trail. Each cast contained from twenty-six to twenty-eight impressions with a median channel equidistant from the two parallel rows of foot-prints, the one made by the feet of the right side, the other by those of the left. In these specimens a greater number of successive foot-marks belonging to one and the same series were displayed than had ever before been observed in any rock ancient or modern. Mr. Abraham has inferred that the breadth of the quadruped was from five to seven inches. A detailed account of the trail was published by Professor Owen, in April 1851, from which the following extracts are made.

"The foot-prints are in pairs, and the pairs extend in two parallel series, with a channel exactly midway between the right and left series. The pairs of the same side succeed each other at intervals, varying from one inch and a half to two inches and a half, the common distance being about two inches. The interval between the right and left pairs, measured from the inner border of the small prints, is three inches and a half, and from the outer border of the exterior or large prints, is seven inches. The shallow median track is one inch and a quarter in breadth, varying in depth, but not in its relative position to the right and left foot prints."

"The inference to be deduced from these characters is, that the impressions were made by a quadruped with the hind feet larger and somewhat wider apart than the fore feet, with both hind and fore feet either very short, or prevented by some other part of the animal's structure from making long steps; and with the limbs of the right side wide apart from those of the left; consequently, that the quadruped had a broad trunk in proportion to its length, supported on limbs either short, or capable only of short steps, and with rounded and stumpy feet, not provided with long claws. There are faint traces of a fine reticulate pattern of the cuticle of the sole at the bottom of some of the foot-prints on one portion of the sandstone; and the surface of the sand is generally smoother there than where not impressed, which, with the rising of the sand at the border of the prints, indicates the weight of the impressing body. The median groove may be interpreted as due either to the abdomen or the tail of the animal; but as there is no indication of any bending or movement of a tail from side to side, it was probably scooped out of the soft sand by a hard breast-plate or plastron. If this were so, it may be inferred that the species was a freshwater or estuary tortoise rather than a land tortoise."[viii-A]

Previously to this discovery, the trias was the oldest stratum in which any remains or signs of a Chelonian had been detected. Numerous other trails have since been observed (1850-51) in various localities in Canada, all in the same very ancient fossiliferous rock; and Mr. Logan, who has visited the spots, will shortly publish a description of the phenomena.

Chelonian foot-prints in Old Red Sandstone, Morayshire.—Captain Lambart Brickenden has just communicated to the Geological Society of London a drawing and description of a continuous series of no less than thirty-four foot-prints of a quadruped observed in the course of last year (1850), on a slab of sandstone quarried at Cummingstone, near Elgin, in Morayshire, a rock which has always been considered as an upper member of the Devonian or "Old Red."[ix-A] A part of the track, the course of which was from A to B, is represented in the annexed woodcut, fig. 521. The foot-prints are in pairs, forming two parallel rows, which are somewhat less distant from each other than those of the Lower Silurian tortoise of Canada above mentioned. The stride, on the other hand, is four inches, or twice that of the Beauharnais Chelonian. The hind foot is exactly of the same size, being one inch in diameter, and larger than the fore foot in the proportion of four to three.

Skeleton of a reptile, allied to the Batrachians, in the Old Red Sandstone of Morayshire.—Mr. Patrick Duff, author of a "Sketch of the Geology of Morayshire" (Elgin, 1842), obtained recently (October, 1851), from the rock above alluded to, the first example ever seen of the skeleton of a reptile in the Old Red Sandstone. He has kindly allowed me to give a figure of this fossil, of which Dr. Mantell has drawn up a detailed osteological account for publication in the "Journal of the Geological Society of London." The bones in this specimen have decomposed, but the natural position of almost all of them can be seen, and nearly perfect casts of their form taken from the hollow moulds which they have left. The matrix is a fine-grained, whitish sandstone, with a cement of carbonate of lime. The skeleton exhibits the general characters of the Lacertians, blended with peculiarities that are Batrachian. Hence Dr. Mantell infers that this reptile was either a freshwater Batrachian, resembling the Triton, or a small terrestrial Lizard. Slight indications are visible of very minute conical teeth. Captain Brickenden, who is well acquainted with the geology of that part of Scotland, informs me that this fossil was found in the Hill of Spynie, north of the town of Elgin, in a rock quarried for building, and the same in which the Chelonian foot-prints, alluded to in the last page, occur. The skeleton is about four and a half inches in length, but part of the tail is concealed in the rock. Dr. Mantell has proposed for it the generic name of Telerpeton, from t??e, afar off, and ??pet??, a reptile; while the specific name Elginense commemorates the principal place near which it was obtained.

Eggs of Batrachians (?) in the Old Red Sandstone of Scotland.—At page 344. of this work I have given two figures (figs. 397 and 398.) of small groups of eggs, very common in the shales and sandstones of the "Old Red" of Kincardineshire, Forfarshire, and Fife. I threw out as a conjecture, that they might belong to gasteropodous mollusca, like those represented in fig. 399. p. 345.; but Dr. Mantell, some years ago, showed me a small bundle of the dried-up eggs of the common English frog (see fig. 524 a.), black and carbonaceous, and so identical in appearance with the fossils in question, that he suggested the probability of these last being of Batrachian origin. The plants by which they are often accompanied (fig. 398. p. 344.), I formerly supposed to be Fuci, but Mr. Bunbury tells me that their grass-like form agrees well with the idea of their being freshwater, and of the family Fluviales.

The absence of all shells, so far as our researches have yet gone, in the slates and sandstones of Scotland above alluded to, raises a presumption against their marine origin, and a still stronger one against the fossil eggs being those of Gasteropoda. It is well known that a single female of the Batrachian tribe ejects annually an astonishing quantity of spawn. Mr. Newport, author of many accurate researches into the metamorphoses of the Amphibia, having examined my fossils from Forfarshire, concurs in Dr. Mantell's opinion that the clusters of eggs (figs. 397. 398. p. 344.) may be those of frogs; while other larger ones, occurring singly or in pairs in the same slates, and often attached to a leaf, may be the ova of a gigantic Triton or Salamander. (See figs. 523, 524, 525.) I may observe that the subdivision of the Old Red Sandstone, in which these plants and ova occur (No. 4. of the section, fig. 62. p. 48.), is considerably lower in position than the rock in which the Telerpeton of Elgin is imbedded.

Foot-prints of Lower Carboniferous reptiles in the United States.—I have stated, at p. 340., that in 1849, Mr. Isaac Lea observed the foot-marks of a large reptile in the lowest beds of the coal formation at Pottsville, about seventy miles N.E. of Philadelphia. These researches have since been carried farther by Professor H. D. Rogers, in the same region of anthracitic coal, lying on the eastern flank of the Alleghany Mountains. Beneath the productive coal-measures of that country occurs a dense mass of red shales and sandstones, which correspond nearly in position to the millstone grit and Mountain Limestone of the south-east of England. In these beds foot-prints, referred to three species of quadrupeds, have lately been detected, all of them five-toed and in double rows, with an opposite symmetry, as if made by right and left feet, while they likewise display the alternation of fore foot and hind foot. One species, the largest of the three, presents a diameter for each foot-print of about two inches, and shows the fore and hind feet to be nearly equal in dimensions. It exhibits a length of stride of about nine inches, and a breadth between the right and left treads of nearly four inches. The impressions of the hind feet are but little in the rear of the fore feet. The animal which made them is supposed to have been allied to a Saurian, rather than to a Batrachian or Chelonian; but more information is required before so difficult a point can be decided. With these foot-marks were seen shrinkage cracks, such as are caused by the sun's heat in mud, and rain-spots, with the signs of the trickling of water on a wet, sandy beach; all confirming the conclusion derived from the foot-prints, that the quadrupeds belonged to air-breathers, and not to aquatic races.[xii-A] The Cheirotherian foot-prints, figured by me at p. 338., in which the fore and hind feet are very unequal in size, betoken a distinct genus, and occur in the midst of the productive coal measures, being consequently less ancient.

On Fossil Rain-marks of the Carboniferous Period in North America.—Having alluded to the spots left by rain on the surface of carboniferous strata in the Alleghanies, on which quadrupedal foot-prints are seen, I may mention that similar rain-prints are conspicuous in the coal measures of Cape Breton, in Nova Scotia, in which Mr. Richard Brown has described StigmariÆ and erect trunks of trees, and where there are proofs, as stated at p. 324., of many fossil forests ranged one above the other. In such a region, if anywhere, might we expect to detect evidence of the fall of rain on a sea-beach, so repeatedly must the conditions of the same area have oscillated between land and sea. The intercalation of deposits, containing shells of marine or brackish water, indicate the constant proximity of a body of salt water when the clays which supported the upright trees were formed. In the course of 1851, Mr. Brown had the kindness to send me some greenish slates from Sydney, Cape Breton, on which are imprinted very delicate impressions of rain-drops, with several worm-tracks (a, b, fig. 526.), such as usually accompany rain-marks on the recent mud of the Bay of Fundy, and other modern beaches.[xii-B]

The casts of rain-prints, in figs. 527. and 528., project from the under side of two layers, occurring at different levels, the one a sandy shale, resting on the green shale (fig. 526.), the other a sandstone presenting a similar warty or blistered surface, on which are also observable some small ridges as at a, which stand out in relief, and afford evidence of cracks formed by the shrinkage of subjacent clay, on which rain had fallen. Many of the associated sandstones are described by Mr. Brown as ripple-marked.

The great humidity of the climate of the coal period had been previously inferred from the nature of its vegetation and the continuity of its forests for hundreds of miles; but it is satisfactory to have at length obtained such positive proofs of showers of rain, the drops of which resembled in their average size those which now fall from the clouds. From such data we may presume that the atmosphere of the carboniferous period corresponded in density with that now investing the globe, and that different currents of air varied then as now, in temperature, so as to give rise, by their mixture, to the condensation of aqueous vapour.

Triassic Mammifer (Microlestes antiquus Plieninger.)—In the year 1847, Professor Plieninger, of Stuttgart, published a description of two fossil molar teeth, referred by him to a warm-blooded quadruped[xiii-A], which he obtained from a bone-breccia in WÜrtemberg occurring between the lias and the keuper. As the announcement of so novel a fact has never met with the attention it deserved, we are indebted to Dr. JÄger, of Stuttgart, for having recently reminded us of it in his Memoir on the Fossil Mammalia of WÜrtemberg.[xiii-B]

Fig. 529. represents the tooth first found, taken from the plate published in 1847, by Professor Plieninger; and fig. 530. is a drawing of the same executed from the original by Mr. Hermann von Meyer, which he has been kind enough to send me. Fig. 529. is a second and larger molar, copied from Dr. JÄger's plate lxxi., fig. 15.

Professor Plieninger inferred in 1847, from the double fangs of this tooth and their unequal size, and from the form and number of the protuberances or cusps on the flat crowns, that it was the molar of a Mammifer; and considering it as predaceous, probably insectivorous, he called it Microlestes, from ?????, little, and ??st??, a beast of prey. Soon afterwards, he found the second tooth also, at the same locality, Diegerloch, about two miles to the south-east of Stuttgart. Some of its cusps are broken, but there seem to have been six of them originally. From its agreement in general characters, it is supposed by Professor Plieninger to be referable to the same animal, but as it is four times as big, it may perhaps have belonged to another allied species. This molar is attached to the matrix consisting of sandstone, whereas the tooth, No. 529., is isolated. Several fragments of bone, differing in structure from that of the associated saurians and fish, and believed to be mammiferous, were imbedded near them in the same rock.

Mr. Waterhouse, of the British Museum, after studying the annexed figs. 529. 531. and the descriptions of Prof. Plieninger, observes, that not only the double roots of the teeth and their crowns presenting several cusps, resemble those of Mammalia, but the cingulum also, or ridge surrounding the base of that part of the body of the tooth which was exposed or above the gum, is a character distinguishing them from fish and reptiles. "The arrangement of the six cusps or tubercles in two rows, in fig. 529., with a groove or depression between them and the oblong form of the tooth, lead him, he says, to regard it as a molar of the lower jaw. Both the teeth differ from those of the Stonesfield Mammalia[xiv-A], but do not supply sufficient data for determining to what order they belonged. Even in regard to the Stonesfield jaws, where we possess so much ampler materials, we cannot safely pronounce on the order."Professor Plieninger has sent me a cast of the smaller tooth, which exhibits well the characteristic mammalian test, the double fang; but Mr. Owen, to whom I have shown it, is not able to recognize its affinity with any mammalian type, recent or extinct, known to him.

It has already been stated that the stratum in which the above-mentioned fossils occur is intermediate between the lias and the uppermost member of the trias. That it is really triassic may be deduced from the following considerations. In WÜrtemberg there are two "bone-beds," one of great extent, and very rich in the remains of fish and reptiles, which intervenes between the muschelkalk and keuper, the other, containing the Microlestes, less extensive and fossiliferous, which rests on the keuper, or superior member of the trias, and is covered by the sandstone of the lias. The last-mentioned breccia therefore occupies the same place as the well-known English "bone-bed" of Axmouth and Aust-cliff near Bristol, which is shown[xv-A] to include characteristic species of muschelkalk fish, of the genus Saurichthys, Hybodus, and Gyrolepis. In both the WÜrtemberg bone-beds these three genera are also found, and one of the species, Saurichthys Mougeotii, is common to both the lower and upper breccias, as is also a remarkable reptile called Nothosaurus mirabilis. The Saurian called Belodon by H. Von Meyer of the Thecodont family, is another Triassic form, associated at Diegerloch with Microlestes.

Previous to this discovery of Professor Plieninger, the most ancient of known fossil Mammalia were those of the Stonesfield slate, a subdivision of the Lower Oolite[xv-B] no representative of this class having as yet been met with in the Fuller's earth, or inferior Oolite (see Table, p. 258.), nor in any member of the lias.

Thecodont Saurians.—This family of reptiles is common to the Trias and Permian groups in Germany, and the geologists employed in the government survey of Great Britain have come to the conclusion, that the rock containing the two species alluded to at p. 306., and of which the teeth are represented in figs. 348, 349., ought rather to be referred to the Trias than to the Permian group.

CRETACEOUS GASTEROPODA.

In speaking of the chalk of Faxoe in Denmark (p. 210.) or the highest member of the Cretaceous series, I have remarked that it is characterized by univalve Mollusca, both spiral and patelliform, which are wanting or rare in the white chalk of Europe. This last statement requires, I find, some modification. It holds true in regard to certain forms, such as CyprÆa and Oliva, found at Faxoe; but M. A. d'Orbigny enumerates 24 species of Gasteropoda from the white chalk (Terrain SÉnonien) of France alone. The same author describes 134 French species of Gasteropoda from the chloritic chalk marl and upper greensand (Turonien), 77 from the gault, and 90 from the lower greensand (Neocomien), in all 325 species of Gasteropoda, from the cretaceous group below the Maestricht beds. Among these he refers 1 to the genus Mitra, 17 to Fusus, 17 to Trochus, 4 to Emarginula, and 36 to Cerithium. Notwithstanding, therefore, the peculiarity of the chambered univalves of various genera, so abundant in the chalk, the Mollusca of the period approximate in character to the tertiary and recent Fauna far more than was formerly supposed.

DICOTYLEDONOUS LEAVES IN LOWER CRETACEOUS STRATA.

M. Adolphe Brongniart when founding his classification of the fossiliferous strata in reference to their imbedded fossil plants, has placed the cretaceous group in the same division with the tertiary, that is to say, in his "Age of Angiosperms."[xvi-A] This arrangement is based on the fact, that the cretaceous plants display a transition character from the vegetation of the secondary to that of the tertiary periods. ConiferÆ and CycadeÆ still flourished as in the preceding oolitic and triassic epochs; but with these fossils, some well-marked leaves of dicotyledonous trees referred to several species of the genus Credneria, had been found in Germany in the Quadersandstein and PlÄner-kalk. Still more recently, Dr. Debey of Aix-la-Chapelle has met with a great variety of other leaves of dicotyledonous plants in the cretaceous flora[xvi-B], of which he enumerates no less than 26 species, some of the leaves being from four to six inches in length, and in a beautiful state of preservation. In the absence of the organs of fructification and of fossil fruits, the number of species may be exaggerated; but we may nevertheless affirm, reasoning from our present data, that in the lower chalk of Aix-la-Chapelle, Dicotyledonous Angiosperms flourished nearly in equal proportions with Gymnosperms; a fact of great significance, as some geologists had wished to connect the rarity of dicotyledonous trees with a peculiarity in the state of the atmosphere in the earlier ages of the planet, imagining that a denser air and noxious gases, especially carbonic acid in excess, were adverse to the prevalence, not only of the quick-breathing classes of animals, (mammalia and birds,) but to a flora like that now existing, while it favoured the predominance of reptile life, and a cryptogamic and gymnospermous flora. The co-existence, therefore, of dicotyledonous angiosperms in abundance with Cycads and ConiferÆ, and with a rich reptilian fauna comprising the Iguanodon, Ichthyosaurus, Pliosaurus, and Pterodactyl, in the lower cretaceous series tends, like the oolitic mammalia of Stonesfield and Stuttgart, and the triassic birds of Connecticut, to dispel the idea of a meteorological state of things in the secondary periods widely distinct from that now prevailing.

General remarks.—In the preliminary chapters of "The Principles of Geology," in the first and subsequent editions, I have considered the question, how far the changes of the earth's crust in past times confirm or invalidate the popular hypothesis of a gradual improvement in the habitable condition of the planet, accompanied by a contemporaneous development and progression in organic life. It had long been a favourite theory, that in the earlier ages to which we can carry back our geological researches, the earth was shaken by more frequent and terrible earthquakes than now, and that there was no certainty nor stability in the order of the natural world. A few sea-weeds and zoophytes, or plants and animals of the simplest organization, were alone capable of existing in a state of things so unfixed and unstable. But in proportion as the conditions of existence improved, and great convulsions and catastrophes became rarer and more partial, flowering plants were added to the cryptogamic class, and by the introduction of more and more perfect species, a varied and complex flora was at last established. In like manner, in the animal kingdom, the zoophyte, the brachiopod, the cephalopod, the fish, the reptile, the bird, and the warm-blooded quadruped made their entrance into the earth, one after the other, until finally, after the close of the tertiary period, came the quadrumanous mammalia, most nearly resembling man in outward form and internal structure, and followed soon afterwards, if not accompanied at first, by the human race itself.

The objections which, in 1830, I urged against this doctrine[xvii-A], in so far as relates to the passage of the earth from a chaotic to a more settled condition, have since been embraced by a large and steadily increasing school of geologists; and in reference to the animate world, it will be seen, on comparing the present state of our knowledge with that which we possessed twenty years ago, how fully I was justified in declaring the insufficiency of the data on which such bold generalizations, respecting progressive development, were based. Speaking of the absence, from the tertiary formations, of fossil Quadrumana, I observed, in 1830, that "we had no right to expect to have detected any remains of tribes which live in trees, until we knew more of those quadrupeds which frequent marshes, rivers, and the borders of lakes, such being usually first met with in a fossil state."[xvii-B] I also added, "if we are led to infer, from the presence of crocodiles and turtles in the London clay, and from the cocoa-nuts and spices found in the isle of Sheppey, that at the period when our older tertiary strata were formed, the climate was hot enough for the Quadrumana, we nevertheless could not hope to discover any of their skeletons, until we had made considerable progress in ascertaining what were the contemporary Pachydermata; and not one of these has been discovered as yet in any strata of this epoch in England."

Nine years afterwards, when these fossil Pachyderms had been found in the London clay, and in the sandy strata at its base, the remains of a monkey, of the genus Macacus, were detected near Woodbridge, in Suffolk; and other Quadrumana had been met with, a short time previously, in different stages of the tertiary series, in India, France, and Brazil.When we consider the small area of the earth's surface hitherto examined geologically, and our scanty acquaintance with the fossil Vertebrata, even of the environs of great European capitals, it is truly surprising that any naturalist should be rash enough to assume that the Lower Eocene deposits mark the era of the first creation of Quadrumana. It is, however, still more unphilosophical to infer from a single extinct species of this order, obtained in a latitude far from the tropics, that the Eocene Quadrumana had not attained as high a grade of organization as those of our own times, when the naturalist is acquainted with all, or nearly all, the species of monkeys, apes and orangs which are contemporary with man.

To return to the year 1830, Mammalia had not then been traced to rocks of higher antiquity than the Stonesfield Oolite, whereas we have just seen that memorials of this class have at length made their appearance in the Trias of Germany. In 1830 birds had been discovered no lower in the series than the Paris gypsum, or Middle Eocene. Their bones have now been found both in England and the Swiss Alps in the Lower Eocene, and their existence has been established by foot-prints in the triassic epoch in North America (p. 297.). Reptiles in 1830 had not been detected in rocks older than the Magnesian limestone, or Permian formation; whereas the skeletons of four species have since been brought to light (see p. 336.) in the coal-measures, and one in the Old Red sandstone, of Europe, while the footprints of three or four more have been observed in carboniferous rocks of North America, not to mention the chelonian trail above described, from the most ancient of the fossiliferous rocks of Canada, the "Potsdam Sandstone," which lies at the base of the Lower Silurian system. (See above, p. vii.)

Lastly, the remains of fish, which in 1830 were scarcely recognized in deposits older than the coal, have now been found plentifully in the Devonian, and sparingly in the Silurian, strata; though not in any formation of such high antiquity as the Chelonian of Montreal.

Previously to the discovery last mentioned, it was by no means uncommon for paleontologists to speak with confidence of fish as having been created before reptiles. It was deemed reasonable to suppose that the introduction of a particular class or order of beings into the planet coincided, in date, with the age of the oldest rock to which the remains of that class or order happened then to have been traced back. To be consistent with themselves, the same naturalists ought now to take for granted that reptiles were called into existence before fish. This they will not do, because such a conclusion would militate against their favourite hypothesis of an ascending scale, according to which Nature "evolved the organic world," rendering it more and more perfect in the lapse of ages.

In our efforts to arrive at sound theoretical views on such a question, it would seem most natural to turn to the marine invertebrate animals as to a class affording the most complete series of monuments that have come down to us, and where we can find corresponding terms of comparison, in strata of every age. If, in this more complete series of her archives, Nature had really exhibited a more simple grade of organization in fossils of the remotest antiquity, we might have suspected that there was some foundation of facts in the theory of successive development. But what do we find? In the Lower Silurian there is a full representation of the Radiata, Mollusca, and Articulata proper to the sea. The marine Fauna, indeed, in those three classes, is so rich as almost to imply a more perfect development than that which now peoples the ocean. Thus, in the great division of the Radiata, we find asteroid and helianthoid zoophytes, besides crinoid and cystidean echinoderms. In the Mollusca of the same most ancient epoch M. Barrande enumerates, in Bohemia alone, the astonishing number of 253 species of Cephalopoda. In the Articulata we have the crustaceans, represented by more than 200 species of Trilobites, not to mention other genera.

It is only then, in reference to the Vertebrata, that the argument of degeneracy in proportion as we trace fossils back to older formations can be maintained; and the dogma rests mainly for its support on negative evidence, whether deduced from the entire absence of the fossil representatives of certain classes in particular rocks, or the low grade of the first few species of a class which chance has thrown in our way.

The scarcity of all memorials of birds in strata below the Eocene, has been a subject of surprise to some geologists. The bones formerly referred to birds in the Wealden and Chalk, are now admitted to have belonged to flying reptiles, of various sizes, one of them from the Kentish chalk so large as to have measured 16 feet 6 inches from tip to tip of its outstretched wings. Whether some elongated bones of the Stonesfield Oolite should be referred to birds, which they seem greatly to resemble in microscopic structure or to Pterodactyles, is a point now under investigation. If it should be proved that no osseous remains of the class Aves have hitherto been derived from any secondary or primary formation, we must not too hastily conclude that birds were even scarce in these periods. The rarity of such fossils in the Eocene marine strata is very striking. In 1846, Professor Owen, in his "History of the Fossil Mammalia and Birds of Great Britain," was unable to obtain more than four or five fragments of bones and skulls of birds from the London Clay, by the aid of which four species were recognized. Even so recently, therefore, as 1846, as much was known of the Mammalia of the Stonesfield Oolite, as of the ornithic Fauna of our English Eocene deposits.

To reason correctly on the value of negative facts in this branch of Paleontology, we must first have ascertained how far the relics of birds are now becoming preserved in new strata, whether marine, fluviatile, or lacustrine. I have explained, in the "Principles of Geology," that the imbedding of the bones of living birds in deposits now in progress in inland lakes appears to be extremely rare. In the shell-marl of Scotland, which is made up bodily of the shells of the genera Limneus, Planorbis, Succinea, and Valvata, and in which the skeletons of deer and oxen abound, we find no bones of birds. Yet we know that, before the lakes were drained which yield this marl used in agriculture, the surface of the water and the bordering swamps were covered with wild ducks, herons, and other fowl. They left no memorials behind them, because, if they perished on the land, their bodies decomposed or became the prey of carnivorous animals; if on the water, they were buoyant and floated till they were devoured by predaceous fish or birds. The same causes of obliteration have no power to efface the foot-prints which the same creatures may leave, under favourable circumstances, imprinted on an ancient mud-bank or shore, on which new strata may be from time to time thrown down. In the red mud of recent origin spread over wide areas by the high tides of the bay of Fundy, innumerable foot-tracks of recent birds (Tringa minuta) are preserved in successive layers, and hardened by the sun. Yet none of the bones of these birds, though diligently searched for, have yet been discovered in digging trenches through the red mud. It is true that, in a few spots, the bones of birds have been met with plentifully in the older tertiary strata, but always in rocks of freshwater origin, such as the Paris gypsum or the lacustrine limestone of the Limagne d'Auvergne. In strata of the same age, in Belgium and other European countries, or in the United States, where no less careful search has been made, few, if any, fossil birds have come to light.

We ought, therefore, most clearly to perceive that it is no part of the plan of Nature to hand down to after times a complete or systematic record of the former history of the animate world. The preservation of the relics, even of aquatic tribes of animals, is an exception to the general rule, although time may so multiply exceptional cases that they may seem to constitute the rule; and may thus impose upon the imagination, leading us to infer the non-existence of creatures of which no monuments are extant. Hitherto our acquaintance with the birds, and even the Mammalia, of the Eocene period has depended, almost everywhere, on single specimens, or on a few individuals found in one spot. It has therefore depended on what we commonly call chance; and we must not wonder if the casual discovery of a tertiary, secondary, or primary rock, rich in fossil impressions of the foot-prints of birds or quadrupeds, should modify or suddenly overthrow all theories based on negative facts.

The chief reason why we meet more readily with the remains of every class in tertiary than in secondary strata, is simply that the older rocks are more and more exclusively marine in proportion as we depart farther and farther from periods during which the existing continents were built up. The secondary and primary formations are, for the most part, marine,—not because the ocean was more universal in past times, but because the epochs which preceded the Eocene were so distant from our own, that entire continents have been since submerged.

I have alluded at p. 299. to Mr. Darwin's account of the South American Ostriches, seen on the coast of Buenos Ayres, walking at low water over extensive mud-banks, which are then dry, for the sake of feeding on small fish. Perhaps no bird of such perfect organization as the eagle or vulture may ever accompany these ostriches. Certainly, we cannot expect the condor of the Andes to leave its trail on such a shore; and no traveller, after searching for footprints along the whole eastern coast of South America, would venture to speculate, from the results of such an inquiry, on the extent, variety, or development of the feathered Fauna of the interior of that continent.

The absence of Cetacea from rocks older than the Eocene has been frequently adduced as lending countenance to the theory of the late appearance of the highest class of Vertebrata on the earth. That we have hitherto failed to detect them in the Oolite or Trias, does not imply, as we have now seen, that Mammalia were not then created. Even in the Eocene strata of Europe, the discovery of Cetaceans has never kept pace with that of land quadrupeds. The only instance cited in Great Britain is a species of Monodon, from the London clay, of doubtful authenticity as to its geological position. On the other hand, the gigantic Zeuglodon of North America (see p. 207.), occurs abundantly in the Middle Eocene strata of Georgia and Alabama, from which as yet no bones of land-quadrupeds have been obtained.

Professor Sedgwick states in a recent work[xxi-A], that he possesses in the Woodwardian Museum, a mass of anchylosed cervical vertebrÆ of a whale which he found near Ely, and which he believes to have been washed out of the Kimmeridge clay, a member of the Upper Oolite; but its true geological site is not well determined. It differs, says Professor Owen, from any other known fossil or recent whale.

In the present imperfect state then of our information, we can scarcely say more than that the Cetacea may have been scarce, in the secondary and primary periods. It is quite conceivable that when aquatic saurians, some of them carnivorous, like the Ichthyosaurus, were swarming in the sea, and when there were large herbivorous reptiles, like the Iguanodon, on the land, such reptiles may, to a certain extent, have superseded the Cetacea, and discharged their functions in the animal economy.

The views which I proposed originally in the Principles of Geology in opposition to the theory of progressive development may be thus briefly explained. From the earliest period at which plants and animals can be proved to have existed, there has been a continual change going on in the position of land and sea, accompanied by great fluctuations of climate. To these ever-varying geographical and climatal conditions the state of the animate world has been unceasingly adapted. No satisfactory proof has yet been discovered of the gradual passage of the earth from a chaotic to a more habitable state, nor of a law of progressive development governing the extinction and renovation of species, and causing the Fauna and Flora to pass from an embryonic to a more perfect condition, from a simple to a more complex organization.The principle of adaptation above alluded to, appears to have been analogous to that which now peoples the arctic, temperate, and tropical regions contemporaneously with distinct assemblages of species and genera, or which independently of mere temperature gives rise to a predominance of the marsupial tribe of quadrupeds in Australia, and of the placental tribe in Asia and Europe, or to a profusion of reptiles without mammalia in the Galapagos Archipelago, and of mammalia without reptiles in Greenland.[xxii-A]

This theory implies, almost necessarily, a very unequal representation at successive periods of the principal classes and orders of plants and animals, if not in the whole globe, at least throughout very wide areas. Thus, for example, the proportional number of genera, species, and individuals in the vertebrate class may differ, in two different and distinct epochs, to an extent unparalleled by any two contemporaneous Faunas, because in the course of millions of ages, the contrast of climate and geographical conditions may exceed the difference now observable in polar and equatorial latitudes.

I shall conclude by observing, that if the doctrine of successive development had been paleontologically true, as the new discoveries above enumerated show that it is not; if the sponge, the cephalopod, the fish, the reptile, the bird, and the mammifer had followed each other in regular chronological order—the creation of each class being separated from the other by vast intervals of time; and if it were admitted that Man was created last of all, still we should by no means be able to recognize, in his entrance upon the earth, the last term of one and the same series of progressive developments. For the superiority of Man, as compared to the irrational mammalia, is one of kind, rather than of degree, consisting in a rational and moral nature, with an intellect capable of indefinite progression, and not in the perfection of his physical organization, or those instincts in which he resembles the brutes. He may be considered as a link in the same unbroken chain of being, if we regard him simply as a new species—a member of the animal kingdom—subject, like other species, to certain fixed and invariable laws, and adapted like them to the state of the animate and inanimate world prevailing at the time of his creation. Physically considered, he may form part of an indefinite series of terrestrial changes past, present, and to come; but morally and intellectually he may belong to another system of things—of things immaterial—a system which is not permitted to interrupt or disturb the course of the material world, or the laws which govern its changes.[xxii-B]