But even much more minute concatenations of form are, by experience, found to exist among the kinds of ani mals, so as to furnish us with marks even far more numer ous and particular than these. Among many organs, where it does not appear a priori that there is a reason for a certain constant relative conformity of structure; such a one does nevertheless exist ; and thus we can infer, even in such cases as this, the nature and form of one part from another, as certainly as if we could trace the reasons why that should be the fact. We have already mentioned, that the masticatory system is least perfect in the quadrupeds that ruminate and have hoofs; and, correspondently, it is more so in those which do not chew the cud, as in the horse, for example, when compared to the ox, as these kinds either possess cutting teeth, or tusks, or sometimes both of those together, in each jaw. Now, it is remark able that in these the structure of the feet is also more complicated ; or they have a greater number of toes, or else the joints of these are not so deeply inclosed in the hoof, or there are more metatarsal and tarsal bones, or a more complete separation between the tibia and the fibula, or else all these pecularities are found existing together. If the reasons of these cannot, as we just observed, be as signed, the facts are not less certain, as is proved by the examination of numerous species in all these animals.
It is thus by having recourse, sometimes to reasoning, and at others to observation, occasionally to both united, that the natures of lost species, or of imperfect fossil re mains, can be determined, and that acute and experienced anatomists are enabled to pronounce on the places in the system of fossil animals, when, to an ordinary observer, there would he nothing but uncertainty and confusion. With respect to any single known species, for example, almost any bone in the body, if it possesses any joint, or tubercle, or specific mark of any kind, is sufficient to de termine what the animal was. Yet geologists, who may flatter themselves that they can decide in this department, must recollect that not only must such power be always limited to those who combine deep anatomical knowledge with much practice, but that success to any extent is scarcely attainable, unless they can also have recourse to large collections of skeletons, with which such fragments as they may be investigating can be compared.
This subject, as a question of Natural History gene rally, is highly interesting. As connected with Geology, it has also its uses in that science, as every department of fossil organic bodies has. It is Cuvier's opinion, that it is infinitely the most valuable part of the general subject for the purposes of geological investigation; a judgment respecting which we cannot feel much surprise, when we recollect how naturally we all learn to overrate that on which we have bestowed the greatest attention, or which has given us the most trouhle. Every thing, as he says,
is here precise. Thus, the presence of bones, and, still more, that of entire skeletons, in any strata, indicate that the stratum in question must have been previously dry, or must, at least, have been associated with dry land. Thus, also, he says that their absence as certainly proves that such a stratum must have been inundated, or must have ceased to be dry land. And thus, he concludes, we establish the important fact of the repeated irruptions of the sea upon the land ; a circumstance which could never be proved by the presence of any other classes of fossil remains.
Had we space to examine these concltisions, from which we are precluded by the limits and nature of this article, we could easily show how hasty many of them are ; but if our geological readers consider them with attention, they will find no difficulty in judging of them, as we might here have done, had our limits permitted. That the nature of the revolutions which changed the form of the earth's surface, must have interfered far more with terrestrial than marine animals, is a conclusion which we have our selves drawn elsewhere. But AI. Cuvicr appears, in all his reasonings on these subjects, to take it for granted, that all the revolutions of the globe consist in a series of deluges ; a conclusion which by no means follows from the facts which he has adduced, and which we are far from thinking proved by any other of the appearances in sup port of it which have yet been brought forward.
But, to quit this subject, we shall only further remark, that, whatever value we may choose to attach to this class of fossil remains in the examination of geological ques tions, their uses are nearly limited to the history of the alluvial strata, and to the very last changes, alone, of the surface of the earth. It is to take a very narrow view of geology indeed, as this able anatomist has every where done, to consider that nothing is worthy of our study in the history of the earth, but that which belongs to its most superficial parts ; that nothing respecting that history is attainable which is not limited to a very short period of time ; and that, having ascertained the species and genera of lost or buried quadrupeds, fishes, and shells, and the nature of the rocks in which these lie, there is nothing more to be done but to sit down satisfied that all beyond it is worthless or unattainable. Geological science may stand on far higher and prouder ground than this ; and we doubt not that a day will arrive, when our knowledge of the earth, of its most distant revolutions and its oldest rocks, shall be as perfect as that of its preserved bones and shells.