428 Darwin, and after Darwin. 



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 else- 

 where, had it not been there destroyed. Now, as a matter of 

 fact, " geological formations of each region are almost in- 

 variably 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 forma- 

 tion 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 un- 

 known 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 suj ply 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 appear- 

 ance ot whole groups of new species in A (X). Now such 



