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 evidence is a proof that the same gradation may be traced in later periods, say in the Tertiary, and between that period and the present; also that the later gradations are finer, so as to leave it doubtful 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 proportion 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 be identical by Des Hayes and Lyell were in reality distinct, although closely allied species."[I-11] Moreover, he is now satisfied, as we understand, 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 this difference in judgment affects almost half of the species!

We pass to a second difficulty in the way of Mr. Darwin’s theory; to a case where we are perhaps entitled to demand of him evidence of gradation like that which connects the present with the Tertiary mollusca.  Wide, very wide is the gap, anatomically and physiologically (we do not speak of the intellectual) between the highest quadrumana and man; and comparatively recent, if ever, must the line have bifurcated.  But where is there the slightest evidence of a common progenitor?  Perhaps Mr. Darwin would reply by another question:  where are the fossil remains of the men who made the flint knives and arrowheads of the Somme Valley?