Chap. IX. IN ANY SINGLE FORMATION. 033 



range ; and wo have soon tliat with plants it is those wliicli 

 have the widest rani>-o, that oftonest present varieties; so that, 

 witli shells and other marine animals, it is pro])able that those 

 which liavc had the widest range, far exceeding the limits of 

 the known geological formations of Europe, have oftcnest given 

 rise, ilrst 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 for- 

 mation. 



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, from the reasons 

 lately assigned, probably short in comparison with that during 

 which it remained without undergoing any ch.ange. 



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, initil many specimens are collected from many 

 ]ilaces ; and, in tlie case of fossil species, this can rarely be 

 effected by paleontologists. "We shall, perhaps, best perceive 

 the improbability of our being enabled to connect species by 

 numerous fine, intermediate fossil links, by asking ourselves 

 ^^•hether, 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 

 alwriginal stocks; or, again, Avhether certain sea-shells inliabit- 

 ing the shores of North America, which are ranked by some 

 conchologists as distinct species from their European represent- 

 atives, 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 discovering in a fossil 

 state numerous intermediate gradations ; and such success is 

 imj>r(>bable in tlu; iiighest degree. 



It has been assorted over and over again, l)y Avritors who 

 believe in the immutability of species, that geology yields no 

 linking forms. This assertion is entirely erroneous. As Sir 

 J. Lubbock has nMuarkod, "Every species is a link between 

 other allied forms." We clearly see this if we take a genus 

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

 lifths of thorn ; for in tliis case no one doubts that the ri'inain- 

 dor will stand much more distinct from each other. If the ex- 

 treme forn)s in the genus happen to have boon thus destroyed, 



