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Show 48 IJAR WINIANA. pages, but even whole alternate chapters, have been lost out, or rather which were never printed from the autographs of Nature. The record was actually made in fossil lithography only at certain times and under certain conditions (i. e., at periods of slow subsidence and places o£ abundant sediment) ; and o:f these records all but the last volume is out of print; and of its pages only local glimpses have been obtained. Geologists, except Lyell, will object to this-some of them moderately, others with vehemence. Mr. Darwin himself admits, with a candor rarely displayed on such occasions, that he should have expected more geological evidence of transition than he finds, and that all the most eminent paleontologists maintain the immutability of species. The general fact, however, that the fossil fauna of each period as a whole is nearly intermediate in character. between the preceding and the succeeding faunas, is much relied on. We are brought one step nearer to the desired inference by the similar "fact, insisted on by all paleontologists, that fossils from two consecutive formations are far more closely related to each other than are the fossils of two remote' formations. Pictet gives a well-known instance-the general resemblance of the organic remains from the several stages of the chalk formation, though the species are distinct at each stage. This fact alone, from its generality, seems to have shaken Prof. Pictet in his firm belief in the immutability of species" (p. 335). What Mr. Darwin now particularly wants to complete his inferential evi¢lence is a proof that the same gradation may be traced in later periods, say in the Tertiary, TilE ORIGIN OF SPEOIES. 49 and between that period and the present; also that the later gradations are finer, so as to leave it doubtfuJ, whether the succession is one of species-believed on the one theory to be independent, on the other, derivative-or of varieties, which are confessedly derivative. The proof of the finer gradation appears to be forthcoming. Des Hayes and Lyell have concluded that many of the middle Tertiary and a large proP? rtion of the later Tertiary mollusca are specifically identical with living species ; and this is still the almost universally prevalent view. But Mr. Agassiz states that,." in every instance where he had sufficient materials, he had found that the species of the two epochs supposed to ~e identical by Des Hayes and Lyell were in reality distinct, although closely allied species." 1 Moreover, he is now satisfied, as we under- · stand, that the same gradation is traceable not merely in each great division of the Tertiary, but in particular deposits or successive beds, each answering to a great number of years; where what have passed unquestioned as members of one species, upon closer examination of numerous specimens exhibit differences which in his opinion entitle them to be distinguished into two, three, or more species. It is plain, therefore, that whatever conclusions can be fairly drawn from the present animal and vegetable kingdoms in favor of a gradation of varieties into species, or into what may be regarded as such, the same may be extended to the Tertiary period. In both cases, what some call species others call varieties; and in the later Tertiary shells 1 "Proceedings of the American Academy of Arts and Sciences·,, vol. iv., p. 178. |