66 De Vi Physica 



type and model of the past, both being, as 

 it were, merely loci, points at which you might 

 cut infinite time. For according to Lyell, 

 geological time was practically infinite : he 

 expressly compares it to astronomical space, 

 overlooking the essential objection (that 

 space is all, whereas the earth is only a very 

 little one). Hence he threw back present 

 conditions into all past periods, and sought 

 to explain the past as though but another 

 present. This is the essence of Lyellian 

 geology. The old man is identified with the 

 child. What Lyell did not understand, and 

 Darwin followed him, was, that the geo- 

 logical process is, not a mathematical and 

 infinite, but an organic process, like the life 

 of an animal or a tree, a thing which 

 runs a course, with a beginning, a middle, 

 and an end : not comparable to parallel 

 lines, but rather to a cone, lines starting 

 from a point and diverging ; or to a spiral, 



