12 De Vi Physica 



dynamically the same. Hence Lyell gave 

 the name of Principles of Geology, and De 

 la Beche that of the Geological Observer, to 

 works devoted to the study of present phy- 

 sical operations : a study in itself the most 

 fascinating in the world. 



But how far this geological uniformitarian- 

 ism was scientifically sound : how far, since 

 Lyell's day, experience has confirmed or 

 rejected it : how far its drafts upon the bank 

 of time can be honoured : how far its minute 

 agents have actually the power attributed to 

 them : how far land is or is not, slowly and 

 imperceptibly, actually rising or sinking : 

 how far earthquakes have or have not power 

 to produce permanent slight alterations in 

 the level of continental areas : how far run- 

 ning water actually has or has not the power 

 of erosion in rock, soft or solid, naked or 

 covered, level or inclined : how far ice- has 

 or has not the power of scooping : how far 



