THE IMPERFECTION OF THE GEOLOGICAI. RECORD 285 



spot. Most marine animals have a wide range; and we have 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 ulti- 

 mately 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 re- 

 sult, as lately insisted on by Dr. Falconer, namely, that the pe- 

 riod 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 per- 

 fect specimens for examination, two forms can seldom be con- 

 nected 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 sev- 

 eral aboriginal stocks; or again, whether certain sea-shells in- 

 habiting the shores of North America, which are ranked by 

 some conchologists as distinct species from their European rep- 

 resentatives, 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 improbable in the highest degree. 



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

 lieve in the immutability of species, that geology yields no link- 

 ing 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 



