20 journal of Travel and Natural History 



to the conclusion, that these hollows have been eroded by forces 

 acting on the surface, it by no means necessarily follows, that the 

 forces so engaged have always been working at the same rate as 

 now. We know of no other agencies in nature capable of per- 

 forming the task, yet they may have done the work sometimes 

 more slowly, sometimes more rapidly, than they do it at the present 

 time. The action may have been the same in kind, without 

 necessarily being always the same in degree. If, indeed, our 





:i- 



Vw,. 7. — N'icw (if l!eM Cliro, I.och Slapiii, Skyc. 



To shew the conical outhne which is apt to be taken by a mass of homogeneous decomposing 

 rock, such as the syenite of Ben Chro. 



planet, and the solar system of which it is a part, \\-x\c been 

 slowly parting with heat, and if heat be the ultimate source from 

 wliich the energy of all natural forces is derived, the present 

 vigour of these forces is perhaps much less than it used to 

 be. In especial, the rate of denudation may have varied, and 

 might have been formerly more rapid than it has now become. 

 This is a question which may be decided either way, without 

 affecting tlic argument of those who, like myself, believe that. 



