Chap. IX. 
GEOLOGICAL EECOED. 
299 
confined to some one spot. Most marine animals liave 
a wide range; and we have seen that with plants it is 
those which have the widest range, that often est present 
varieties; so that with shells and other marine animals^ 
it is probably those which have had the widest range, 
far exceeding the limits of the known geological forma¬ 
tions of Europe, which have oftenest given rise, first 
to local varieties and ultimately to new species; and 
this again would greatly lessen the chance of our being 
able to trace the stages of transition in any one geo¬ 
logical formation. 
It should not be forgotten, that at the present day, 
with perfect specimens for examination, two forms can 
seldom be connected by intermediate varieties and thus 
proved to be the same species, until many specimens 
have been collected from many places; and in the case 
of fossil species this could rarely be effected by palae¬ 
ontologists. We shall, perhaps, best perceive the im¬ 
probability of our being enabled to connect species by 
numerous, fine, intermediate, fossil links, by asking our¬ 
selves whether, for instance, geologists at some future 
period will be able to prove, that our different breeds of 
cattle, sheep, horses, and dogs have descended from a 
single stock or from several aboriginal stocks; or, again, 
whether certain sea-shells inhabiting the shores of North 
America, which are ranked by some conchologists as 
distinct species from their European representatives, 
and by other conchologists as only varieties, are really 
varieties or are, as it is called, specifically distinct. This 
could be effected only by the future geologist discover¬ 
ing in a fossil state numerous intermediate gradations; 
and such success seems to me improbable in the highest 
degree. 
Geological research, though it has added numerous 
species to existing and extinct genera, and has made the 
