many pteropods of larger bulk than those now existing, of the chambered shells of many singular cephalopods (Orthoceratites, &c.), and the shells of some gasteropod and bivalved mollusca. Ascending to the carboniferous formations of this silurian epoch, the molluscan fossils thicken upon us. Brachiopods abound under novel forms; a larger number of gasteropods and of ordinary bivalves have appeared to aid in the great work; "but the cephalopodous inhabitants of the seas during the carboniferous period were still the most important and the most numerous of the molluscous animals; and they included not only the straight shells of Orthoceratites, but a large number of spirally twisted species, bearing a somewhat different relation to the nautilus. The most important are called Goniatites." * It is from these strata that lime is principally worked; and in the marble of which your chimney-piece is made, you may trace the figures of shells that have been pictured there by no sportive freaks of the formative powers of nature, nor by a spontaneous vegetation, as philosophy once dreamed, but that are the real remains of living creatures which "have put off flesh and blood, and are become immutable."-Ascending to the middle epoch, we find, indeed, the former races. to have disappeared, but their places are fully occupied by others approximating nigher in character to those of existing seas, "without any of the species being identical, and with little approach even to existing genera. A very large number were among the common tenants of the lias, both brachiopods and bivalved and univalved mollusks; and another large and important group called Ammonites, related to the existing Nautilus. The Belemnite, which was a naked cephalopod allied to the Sepia, was also a common animal, and, with the Ammonites, so thronged some parts of the sea that complete strata seem to have been formed of their remains. In the oolitic seas mollusca swarm even more abundantly: some Terebratulæ, in certain localities, lived in beds as oysters now do almost to the exclusion of other animals; the Ammonite was scarcely less abundant than in the preceding period; and the Belemnite now occurs in the highest perfection, varying in size from specimens not an inch long to others measuring upwards of a foot.The succeeding cretaceous period owes not less to its molluscan tenants, and their fossils truly indicate their influence. Bivalved and univalved genera thronged the waters; and the

*Ansted's Ancient World, 96. In this popular and pleasant volume, the student will find the successive creations of the mollusca carefully indicated, and good figures of the most remarkable and characteristic species.

cephalopods, ere long destined to be dismissed from among the workers which were operating so assiduously to fit this globe for man's tenancy," seem to have expanded into a vast multitude of strange forms before becoming finally extinct."-We step on into the modern epoch; and there, too, the mollusca accompany us-different, indeed, in species from all that had preceded them, but alike in this work of contribution to our earth's perfection. The Ammonites have died out, and their place and purpose is occupied and fulfilled. by carnivorous gasteropods, in their spiral shells, created in the most remarkable profusion. The Nummulites-small shells of doubtful classification-also abound, and are so incredibly multitudinous in some localities that rocks are made up of them. "Other smaller foraminiferous shells have built great masses of the limestone of this period." They enter so largely into the composition of the stones of which Paris is built, that it may be said without exaggeration that that great city is built of shells. *This very general statement is sufficient for the purpose in view, of indicating the vast influence the mollusca have had in their capacity as assistant-architects of our world; but to make their remains subservient to geology, the conchologist has to go more narrowly to work, he has to ascertain the species which occur in every layer, if I may so speak, of every strata; to mark those which are peculiar to each; to note the variations they have undergone in their transition from one formation to another; the times of their creation-of their chief predominance of their decay and extinction; and to specify what new forms come to supply the place of those which are about to disappear, or which have been erased from the volume of living entities. From such researches, which have been conducted with a zeal and ability that cannot be too highly praised, geologists have borrowed largely; and though the value of the evidence which fossil shells afford in unravelling the mutations of the earth is variously estimated, yet it seems agreed on all hands that it would be as wise for the historian in tracing the history and manners of an ancient people to neglect their medals and their monuments, as for the geologist to overlook the light thrown over his antiquarian researches by these medals of the ancient world. "The different series of formations," says the Rev. Mr. Conybeare, "differ very materially in the species of organic remains which they include, and by which they are, therefore, said to be characterised. The species frequently vary from form

* Desc. de Coq. car. des Terrains, 253.-Dr. J. P. Smith's Script. Geol. 98.

ation to formation, so that they have been said, almost without exaggeration, to be as regularly disposed in the geological formations as in the drawers of a well-arranged museum; hence if the fossils of any given locality be known, we may securely pronounce as to its geological formation, and vice versâ.”*

Mr. Lyell has divided the tertiary formations into three periods; and it has been ascertained by Deshayes, that as we proceed from the lowest of these to the most recent, there is a gradually increasing approximation to the existing forms of nature: in the lowest, or eocene, there are only three testaceous mollusks in the hundred identical with existing species; in the mid, or meiocene, there are nineteen ; but in the uppermost, or pleiocene, the proportion is upwards of a half, or fifty-two per cent. During this latest period, however, the mollusks continued to effect very considerable deposits, less in extent, it may be admitted, than in previous epochs when the secondary and carboniferous limestones were formed, but still sufficient to vindicate their claims to be, among animated beings, the most influential of any, excepting zoophytes, in altering the relation between sea and land. Examples of these deposits abound in the north and south of Europe in general, in Asia and Africa, and in New Holland; but we select one only as an illustration of our position.

In France, in the neighbourhood of Touraine, there is a continuous bed of broken shells, of about nine ancient square leagues in superficial extent, and at least twenty feet in thickness: the whole mass of shells is estimated at 170 millions of cubic tons!+ Such facts seem to warrant the inference, that the living mollusks continue to be powerful cooperative agents in bringing about those changes which slowly and imperceptibly are imprinting an altered character on the features of our earth; and it is so. In Europe there are everywhere remarkable beds of shell-marl, abounding with the remains of lacustrine mollusca, which certainly constitute a very material part of its bulk; and by these depositions lakes and marshes have been filled up to a great extent. Beaches composed of dead sea-shells are

*West of Eng. Journ. i. 3.-"Conchology, studied in a logical manner in its various relations both to zoology and geology, may become a powerful means of bringing this latter science to perfection. It is even allowable, in the present day, to anticipate the time when Conchology shall arrive at questions which relate to the general physics of the terrestrial globe, and furnish us with the necessary materials for their solution."-DESHAYES, Mag. Nat. Hist. n. s. i. 9.

+ Malté-Brun's Geog. ii. 268-272.- Jameson in Brewster's Edinb. Encyclop. xv. 735.

found scattered through the world, the mass being the remains of some gregarious species, such as the oysters, which the sea has left uncovered in its retreat, or which, by their increase near the mouths of rivers, have forced the stream to seek another entrance into the ocean. For proofs of their efficacy to this purpose, we need not travel abroad, though undoubtedly the more remarkable of them are, as you might anticipate, to be found in warm and tropical climates, where life is more prolific than in the moderate temperature of Europe, and productive of larger growths. In Senegal, Adanson mentions that in the tide-way of the Del, not far from the mouth of the Niger, the village of Del is built on the extremity of a bank of shells, which extends nearly a league to the north; all this enormous bank being solely composed of the valves of the tree-oyster that had once lived there pendant from the roots of the mangol-trees, but had been left dry by a change in the course of the river, that change effected by their own natural increase.* The same traveller describes another bank formed in a similar manner, by the same species of oyster, which is of still greater extent, and gives name to a district of Senegal-le quartier de la Chaux,"-because the whole country is thence furnished with all its lime.† America supplies us with some remarkable examples of the same kind, where at the mouth of many of its large rivers, a little elevated above the tide, there are extensive beds of the Ostrea virginica mixed with some littoral shells in a subfossil state. Anastasia Island, upon the eastern coast of Florida, which is about ten or twelve miles long, and one and a half broad, "is composed of horizontal layers of a

* Voy. au Sénégal, 128.

+ Ibid. 147.

Dr. Rogers adds-" The position in which these beds of shells are invariably seen, is upon the low level plains adjacent to the tide-creeks of our rivers, where they appear to have dwelt in colonies in the sheltered bays at a time when these plains were at a small depth beneath the water, and to have been lifted with them by, perhaps, the last shock which has changed the level of the coast. These shells, in a sub-fossil state, occur in Cumberland county, New Jersey, on the bank of Stow Creek, at Egg Harbour, on the Severn, at Euston, in Maryland; again, upon the York River in Virginia, and indeed upon many others of the southern rivers. They occur at the mouth of the Potomac, resting upon the beds of marine shells, which were originally described in the Journal of the Academy of Natural Sciences, by Mr. Conrad, and considered by him as referable to the newest of our fossiliferous formations. In the same locality, these beds of fossil Ostrea virginica are seen to be covered by the diluvium, so that there can be no question of their origin having been during the latest stage, as it were, of the tertiary period, and not connected, as imagined by the vulgar, with human agency."-Fourth Report of Brit. Assoc. 17.-See also Bosc's Coquil. ii. 295.

semi-indurated rock, consisting wholly of fragments of shells, belonging, as far as examined, almost, though not exclusively, to species inhabiting the adjoining coast." There are similar islands and beaches on the coasts of Georgia and Florida; and Dr. Rogers believes, that most of the other sand beaches and islands which lie along the coast of North America, as far as Long Island, have the same origin. We do not say that these shells, by their aggregation, gave of themselves origin to the islands in question, but it is very evident that they have materially contributed to it: probably the layers of shell-rock are the result of vast colonies of bivalve and other shell-fish which had settled on sandbanks, and been lifted up afterwards above the waters by the agency of earthquakes. A deposit, composed entirely of two existing shells, in a subfossil state, the Cyrena carolinensis, and more especially the Rangia cyrenoides of Des Moulins, extends along the whole shore of the Gulf of Mexico from Pensacola to Franklin in Louisiana, bends round Mobile Bay, Lake Poutchantrain, and ranges across the delta of the Mississippi immediately above its marshes, a total distance of nearly three hundred miles, and probably much further! It is remarkable that the shells "occur in beds with scarcely any admixture of sand or earth, and they are consequently found extremely useful in repairing roads, and paving the streets of the city. They are dug from the surface of the soil, both on the main shore and the islands of the bay. These deposits border the bays of the Gulf of Mexico between Mobile and New Orleans, and they occur in the vicinity of Franklin, Louisiana. The Ohandeleur Isles, between Mobile Bay and the delta of the Mississippi, consist of deposits of these shells covered by a fertile soil. The Rangia lives in vast numbers in the extensive flats below Mobile, burrowing three or four inches beneath the surface of the sand, in which numerous depressions indicate where they are to be found."*

There is reason, therefore, to believe that the exuvial coverings of the mollusca continue to be heaped up in the dark unfathomed caves of ocean, to become, at some future period, and under the pressure and influence of conjectural agencies, the material constituents of calcareous banks or

*Fourth Report of Brit. Association, 14, 30. Near Valparaiso, there are great beds of shells, which are elevated some yards above the level of the sea. They nearly all consist of one species of Erycina; and these shells at the present day live together in great numbers on the sandy flats. So wonderfully numerous are those forming the beds, that for years they have been quarried and burnt for the lime, with which the large town of Valparaiso is supplied."— C. DARWIN, Voy. of Adv. and Beagle, iii. 310.—See also vol. ii. p. 421.