262 ABSENCE OF INTERMEDIATE VARIETIES [CHAP. X, 



spot. Most marine animals have a vide range ; and we hare 

 seen that with plants it is those which have the widest range, 

 that oftenest present varieties ; so that, with shells and other 

 marine animals, it is probable that those which had the widest 

 range, far exceeding the limits of the known geological formations 

 in Europe, 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 geological formation. 



It is a more important consideration, leading to the same 

 result, as lately insisted on by Dr. Falconer, namely, that the 

 period during which each species underwent modification, though 

 long as measured by years, was probably short in comparison 

 with that during which it remained without undergoing any 

 change. 



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 are collected from many places ; and with 

 fossil species this can rarely be done. We shall, perhaps, best 

 perceive the improbability of our being enabled to connect species 

 by numerous, fine, intermediate, fossil links, by asking ourselves 

 whether, for instance, geologists at some future period will be 

 able to prove that our different breeds of cattle, sheep, horses, 

 and dogs are 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 con- 

 chologists 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 

 by the future geologist only by his discovering in a fossil state 

 numerous intermediate gradations ; and such success is im- 

 probable in the highest degree. 



It has been asserted over and over again, by writers who 

 believe in the immutability of species, that geology yields no 

 linking forms. This assertion, as we shall see in the next chapter, 

 is certainly erroneous. As Sir J. Lubbock has remarked, " Every 

 "species is a link between other allied forms." If we take a genus 

 having a score of species, recent and extinct, and destroy four- 

 fifths of them, no one doubts that the remainder will stand much 

 more distinct from each other. If the extreme forms in the genus 

 happen to have been thus destroyed, the genus itself will stand 

 more distinct from other allied genera. What geological research 

 has not revealed, is the former existence of infinitely numerous 

 gradations, as fine as existing varieties, connecting together nearly 

 all existing and extinct species.. But this ought not to be expected ; 



