Chap, XV.] CONCLUSION. 295 



ably sterile, and varieties invariably fertile; or th at 

 s terility is a special en jlogm£nt__aj3^sign_j3L creation^ 

 Th e belief that species were immutabl e productions jwas_, 

 almost unavoidab le as long as thel^stor y of thewo rld_ 

 was thoug ht to be of short duration ; and now that we 

 ""have acquired some idea of thelapse_ of time, we are too ^ 

 apt to assum e_ffiithau t proof, t£ atI^e_geological record_ 

 is so perfect that it wouldi i a . vc affor dcri i n p inin o v irlp iirn 

 , of the mutation of species, if they had undergone 

 A mutatiofl, ^ 



J^ rSut the chief cause of our natural unwillingness to 

 ii aomit that one species has given birth to other and 

 distinct species, is that we are always slow in admitting 

 great changes of which we do not see the steps!\ The 

 difficulty is the same as that felt by so many geologists, 

 when Lyell first insisted that long lines of inland cliffs 

 had been formed, and great valleys excavated, by the 

 agencies which we see still at work, ^he mind cannot 

 possibly grasp the full meaning of the term of even a 

 million years ; it cannot add up and perceive the full 

 effects of many slight variations, accumulated during an 

 almost infinite number of generationsTj 



Although I am fully convinced oTthe truth of the 

 views given in this volume under the form of an abstract, 

 I by no means expect to convince experienced naturalists 

 whose minds are stocked with a multitude of facts all 

 viewed, during a long course of years, from a point of 

 view directly opposite to miue-Vlt is so easy to hide 

 our ignorance under such expressions as the " plan of 

 creation," " unity of design," &c., and to think that w 

 give an explanation when we only re-state a facT7 ]6 Any- 

 one whos e disposition leads him to attach more weight 

 to unexplained difficulties than to the explanation 'oTa 



