But when we come to examine the details on which this opinion rests, they are far from being satisfactory. Ac cess to the depths of the sea is so difficult, that we cannot presume that we are acquainted with all its inhabitants; and it is impossible, therefore, to pronounce an absolute negative with respect to any one fossil shell in nature, or to any one marine ar.itnal. We cannot even be justified in first searching for the living resemblances of the an cient fossils in the seas nearest to those places where they are now found, and then, from their absence, pronouncing on their extinction; because it is not absolutely decided that the climates of the globe have not uncler gone impor tant changes. It does not, indearl, appear how a question of this nature can ever be determined; and if, as has re cently been proved to be the case, greater care in the in vestigation of shells, both recent and pc trifled, shall prove that the resemblances are more numerous than was once imagined, we are entitled, for the present, to suspend our judgments on this question, as far as it depends on evi dence of this nature. If, as noticed in a former part of this at ticle, the earlier animals have been exposed to the particeiar consequences of general revolutions, as there suggest( d, then, in, ced, we may perhaps conclude, that, prior to •k point of time, all genera and species are e:KtIrc • •.111e general revolutions are admitted to r. at any subsequent period, the same ar g be extended; and we must then limit our 2 ". t esemblanccs, accordingly, to those fossils that at- teo.let! in the strata which follow the red marl, or, st lartht:r, to those that occur above the chalk.
,rut this ar:mment respecting the possible or probable e.,.!inetions of the earlier animals, is purely hypothetical, since it rests on suppositions that never can be proved. Even admitting that the early races had been extermina there in no reason why new genera, or even new spe cies, should not have been created on the models of those that were thus destroyed. But, instead of entangling our selves in metaphysical reasonings, let us examine how the fact stands, as far as the evidence goes. It will be seen that genera are found in ancient strata similar to those now existing: to know how far and how wide the corres pondence among species extends must be a work of time. It must be observed, however, that even in this abstract question of identities, there may be an uncertainty. The characters of genera are constructed by rules which na turalists have laid down ; and these, being founded on cer tain ostensible forms, may not correspond to those by which nature has regulated the characters and divisions of her families.
In the argillaceous schists of the ancient series, there are found echini, terebratulze, turbines, chama:, and tel linte; and every one of these genera are now existing.
Patella:, nautilx, anomize, and even crabs, are found in the mountain, or lowest secondary limestone, and these also are existing genera. It is almost unnecessary to Porsue this examination further ; as here are instances of genera corresponding with the present, both previous to the great interval which separates the primary frOm the secondary rocks, and subsequent to it. As to the correspondence of species between the present state of the earth and these two extreme points, this is also one of the cases in which we cannot prove a negative. Not only are the fossil•ani mals rare, but they are often so imperfect that their spe cific distinctions are destroyed; while we are equally on acquainted with all the existing species which we ought to possess before deciding•on this question.
IF now we ascend higher in this series, commencing with the lias, as posterior to that change in the disposition of the earth's surface which also appears to have been a very general one throughout the globe, we find the cor respondences to the living genera materially increased in number. In that association of strata there are found, for example, astcria, chama, donax, ostrea, helix, trochus, and many others; while, above it, up to the chalk inclu sive, we also meet with patella, halanus, turbo, buccinum, pinna, murex, and other genera, together with tortoises.
If the question of corresponding species remains still doubtful here also, it must be attributed to the causes al ready mentioned. But, in the uppermost strata of all, na turalists seem to have been satisfied of the correspondence even of many species among fossil shells with those still existing. It is unnecessary for us to give a list of these; since the truth of the statement must depend on that mi note knowledge and experience which conchologists only can possess, and which we have no room to examine here.
The correspondence of genera and species in the larger animals, chiefly terrestrial, which are found most com monly in the alluvial soils, has been ascertained in many cases by authority, which no one will dispute, to wit, that of Cuvicr. And in these examples, the size of the ani mals, and the certainty and number of the indications drawn from their complicated anatomy, should leave no doubt respecting their real natures. Of seventy-eight quadrupeds, it is found that eleven or twelve are now ex isting, and that sixteen or eighteen are doubtful. Respect ing some of the others which appear to have no parallels at present, we cannot be certain, because we have by no means explored those parts of Asia, America, Africa, or New Holland, where they may, for aught we know, still be concealed.
As Cuvier is, however, of opinion that very little pro bability exists of now discovering any new quadrupeds, we owe it to our readers to give an abstract of his reason ings on this subject.