VI.] SPECIES AND TIME. 161 



astronomy seem able to allow for the completion of the 

 process. 



Finally, a difficulty exists as to the reason of the absence 

 of rich fossiliferous deposits in the oldest strata — if life 

 was then as abundant and varied as, on the Darwinian 

 theory, it must have been. Mr. Darwin himself admits ^ 

 " the case at present must remain inexplicable ; and may 

 be truly urged as a valid argument against the views '^ 

 entertained in his book. 



Thus, then, we find a remarkable (and on Darwinian 

 principles an inexplicable) absence of minutely graduated 

 transitional forms. All the most marked groups — bats, 

 pterodactyles, chelonians, ichthyosauria, anoura, &c. — 

 appear at once upon the scene. Even the horse, the animal 

 whose pedigree has been probably best preserved, affords 

 no conclusive evidence of specific origin by insignificant 

 fortuitous variations ; while some forms, as the labyrintho- 

 donts and trilobites, which seemed to exhibit gradual 

 change, are shown by further investigation to do nothing 

 of the sort. As regards tlie time required for evolution 

 (whether estimated by the probably minimum period re- 

 quired for organic change, or for the deposition of strata 

 which accompanied that change), reasons have been sug- 

 gested why it is likely that the past history of the earth 

 does not supply us with enough. First, because of the 

 prodigious increase in the importance and number of 

 differences and modifications which we meet with as we 

 traverse successively greater and more primary zoological 

 groups ; and, secondly, because of the vast series of 

 strata necessarily deposited if the period since the 

 Lower Silurian marks but a small fraction of the whole 



1 " Origin of Species," 5th edition, p. 381. 



M 



