While the cultivators of the living departments of na ture arrange and describe these objects, it is for the geolo gist especially to determine their antiquity, by the posi tions and relations of the rocks or alluvia in which they may be imbedded. It is he alone, also, who can truly dis cover by the natures of the rocks what were the earths which they frequented; the yet unconsolidated materials in which they lived and died. It is his duty, also, either to ascertain, by geological observations and anologies, what were the fluids which they inhabited ; whether they lived in the land or under the sea, in fresh water or in salt; or, at least, to confirm by geological phenomena the evidence which zoology or botany may produce on this subject. Thus, also, it belongs to him to show, under what states of the earth such living beings should sometimes have in habited fresh waters on its surface, while at others they resided beneath the sea; to explain why terrestrial and marine animals are found intermixed, and why, in some cases, they alternate. The geologist also must assign rea sons why those animals, which once occupied the surface of the loose earth, beneath the water, are now imbedded in solid rocks; why, once living at the bottom of a deep ocean, they now occupy places on the highest mountains; and why, when originally packed in horizontal beds, they are now accumulated in a similar manner in strata elevated at high angles, or disturbed in many irregular ways. It is also for him to assign a reason why they are abundant in some kinds of rock, while there are others in which they are never found; why they are partial; why their deposits are interrupted by strata that contain none ; and why they show so many different attachments to particular strata, whether with respect to their natures or their relative places in the series of rocks.
It is for geology, also, to account for the appearances and all the attendant circumstances of those organic bo dies, of comparatively recent date, and, in some cases, in deed, of dates even within the records of history, which are found in the land and in its loose alluvial surface. It is the business of that science to show how they were en tangled in these alluvia; whence they were derived, and how accumulated; and how the waters which must have covered as it deposited many of them, have disappeared. To show why the remains of the inhabitants of the sea now sometimes occupy the same alluvia as those of land animals, is also within the department of the geologist. It is further his province to inquire, if any facts exist to prove that which is suspected from the analogies and places of many organized bodies ; namely, whether certain parts of the earth have undergone changes of climate; whether there is any probability that the axis of the globe has experienced any alteration of its position in former times. It has also been sometimes imagined, that many such animals, or their remains, have been transported to their present situations by deluges. Here the geologist may confirm, or otherwise, the evidence which is deduci ble from the appearance of these remains, by those pheno mena of another nature which are more peculiarly the objects of his science.
Almost every thing, indeed, which renders this branch of natural history peculiarly interesting, is in the province of the geologist. It is his science which explains diffi culties, and assigns causes for the several phenomena. It is geology which connects with the history of the earth itself, that of the different races of beings by which it was inhabited, or by which it is still possessed ; as unassisted zoology and botany connect together those races that have long ceased to exist, with the present inhabitants. It is
not the object, however, of these remarks, to enter into details of a more minute nature respecting this extensive subject. Neither can we neie pretend to show how the several geological facts and reasonings to which we Haut thus alluded, may be brought to bear on these and on many other cases that might have been enumerated. To enter on them in such a manner, would be to involve a very con siderable part of the general details of geology ; to write no small portion of a work on that wide subject. The geo logist who has mastered his science, or, at least, as much of it as is yet known, is prepared to enter on such reason ings wherever they may be requisite; as far, at any rate, as facts can assist him ; and the remainder must be trusted to the power which he has acquired over his tools. It is by the use of these, that he will distinguish himself from the mass of observers which is content to dwell for ever among trifles; a weed, a shell, or a bone, the shape of an alcyonium, or the anatomy of a rhinoceros.
But the knowledge of fossil remains has a use indepen dent of that which leads to their own history, even in its most extended and interesting sense. It often affords evi dence, either absolute or collateral, of great value, respect ing the more purely geological history of rocks. The na ture of this evidence must, in some respects, be well known to all those who may read this essay as geologists ; yet it will not be out of place to give a slight sketch of it, and of the subjects to which it is principally applicable.
Whatever doubts might exist respecting the deposition or formation of certain rocks under the waters of the sea, are fully removed by the presence of marine shells in them; and w here these strata alternate with, or are, in particular modes, connected with others, that contain no such bodies, the same proofs involve both. Thus also the fact of the elevation of the strata, or of the retiring of the sea, at least, is proved, or confirmed, since there is no want of other proofs of these changes. In the same way the relative po sition of peculiar shells to the planes of the stratification, prove that they were originally in a horizontal or slightly inclined position, although now highly inclined, or even vertical. Thus, among'living shells we find certain worms Inhabiting cylindrical or conical shells, whose instinct it is always to bury themselves in the stratum of mud or sand which they inhabit, in a vertical position, or at the right angles to the plane of the stratum. Now, when such shells are found in the fossil state, they still stand at the same angle with regard to their bed ; although, when these strata are highly elevated, it is plain that they can no longer be at right angles to the horizon. Hence it is inferred, and that securely, that these strata have been moved from their original positions, just as certainly as that they have been elevated out of the waters of the sea. Similar arguments. and equally satisfactory, are derived from the positions of flat and of concave bivalve shells in the elevated strata. In water, the flat ones must necessarily subside in a hori zontal position ; while the concave single shells of bivalves must also repose with their convex sides downwards. Thus the original position of the stratum is easily ascertained, and the changes which it has experienced inferred.