IMPERFECTION OF GEOLOGICAL RECORD 79 



was probably short in comparison with that during which 

 u 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 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 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 conchologists as 

 distinct species from their European representatives, and 

 by other conchologists as only varieties, are really varie- 

 ties, 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 grada- 

 tions; and such success is improbable 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 be- 

 tween 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 ex- 



