But no doubt a greater difficulty arises where whole groups of species and genera, or even families and orders, appear to arise suddenly, without anything leading up to them. Even this the second difficulty, however, admits of being fully met, when we remember that in very many cases it has been proved, quite apart from the theory of descent, that superjacent formations have been separated from one another by wide intervals of time. And even although it often happens that intermediate deposits which are absent in one part of the world are present in another, we have no right to assume that such is always the case. Besides, even if it were, we should have no right further to assume that the faunas of widely separated geographical areas were identical during the time represented by the intermediate formation. Yet, unless they were identical, we should not expect the fossils of the intermediate formation, where extant, to yield evidence of what the fossils would have been in this same formation elsewhere, had it not been there destroyed. Now, as a matter of fact, "geological formations of each region are almost invariably intermittent"; and although in many cases a more or less continuous record of past forms of life can be obtained by comparing the fossils of one region and formation with those of another region and adjacent formations, it is evident (from what we know of the present geographical distribution of plants and animals) that not a few cases there must have been where the interruption of the record in one region cannot be made good by thus interpolating the fossils of another region. And we must remember it is by selecting the cases where this cannot be done that the objection before us is made to appear formidable. In other words, _unless_ whole groups of new species which are unknown in formation A appear suddenly in formation C of one region (X), where the intermediate formation B is absent; and _unless_ in some other region (Y), where B is present, the fossiliferous contents of B fail to supply the fossil ancestry of the new species in A (X); _unless_ such a state of matters is found to obtain, the objection before us has nothing to say. But at best this is negative evidence; and, in order to consider it fairly, we ought to set against it the cases where an interposition of fossils found in B (Y) _does_ furnish the fossil ancestry of what would _otherwise_ have been an abrupt appearance of whole groups of new species in A (X). Now such cases are neither few nor unimportant, and therefore they deprive the objection of the force it would have had if the selected cases to the contrary were the general rule. In addition to these considerations, the following, some of which are of a more special kind, appear to me so important that I will quote them almost _in extenso_.