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, asa 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, wzless 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 wnless 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); wz/ess 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 o/herwzse have been an abrupt appear- 
ance oi whole groups of new species in A (X). Now such 
