106 EXPEDITION OF THE "CHALLENGER" m 



broad fact that, the lower we go in the scale of 

 organization, the fewer signs are there of con- 

 vergence towards the primitive form from whence 

 all must have diverged, if evolution be a fact. 

 Nevertheless, that it is a fact in some cases, is 

 proved, and I, for one, have not the courage to 

 suppose that the mode in which some species have 

 taken their origin is different from that in which 

 the rest have originated. 



What, then, has become of all the marine 

 animals which, on the hypothesis of evolution, 

 must have existed in myriads in those seas, wherein 

 the many thousand feet of Cambrian and Lauren- 

 tian rocks now devoid, or almost devoid, of any 

 trace of life were deposited ? 



Sir Charles Lyell long ago suggested that the 

 azoic character of these ancient formations might 

 be due to the fact that they had undergone 

 extensive metamorphosis ; and readers of the 

 " Principles of Geology " will be familiar with the 

 ingenious manner in which he contrasts the theory 

 of the Gnome, who is acquainted only with the 

 interior of the earth, with those of ordinary 

 philosophers, who know only its exterior. 



The metamorphism contemplated by the great 

 modern champion of rational geology is, mainly, 

 that brought about by the exposure of rocks to 

 subterranean heat ; and where no such heat could 

 be shown to have operated, his opponents as- 

 sumed that no metamorphosis could have takeu 



