12 Sir Charles Lyell and Modem Geology. [Jan., 



as its ultra-antagonist, the theory of marine denudation, pur et 

 simple, does in the other ; and it is not surprising that Sir Charles 

 Lyell should refuse to give his support to either. It is perfectly 

 possible that atmospheric causes may have produced a greater effect 

 in particular regions than even Sir Charles himself was able to 

 prove in the ' Principles ; ' but that is quite a different issue, and 

 merely a further proof of the doctrine of uniformity. which he has 

 advocated for so many years. 



It would occupy too much space to recount the arguments that 

 may be urged in support of the different theories of erosion and 

 denudation ; but it may be remarked generally, that phenomena of 

 so varied a character are not, as a rule, referable to the same cause. 

 Certain valleys generally considered to have been scooped out by 

 the sea may have been excavated by rain and rivers, or vice versa ; 

 but a multitude of such instances, unless they embrace every possible 

 character of valley and circumstance of occurrence, is not sufficient to 

 warrant the general conclusion that all valleys have been formed by 

 one agent, or by the other. 



Another phase of the question is that respecting the meaning to 

 be attached to the expression " form of the ground," this having 

 been very recently the subject of discussion. If the very latest and 

 smallest modifications of the surface are taken into account, of 

 course the present " form of the ground " is due entirely to atmo- 

 spheric agencies, not excepting volcanic cones and craters ; but if 

 this interpretation be insisted on, — why scientific discussion has 

 degenerated into quibbling. 



The theory of the formation of lake-basins by glacial erosion is 

 fundamentally new, and has received from Sir Charles Lyell, in the 

 last edition of the ' Elements,' and in a work to which we have 

 not yet referred,* a fuller examination than the " subaerial denuda- 

 tion " hypothesis, which is merely an old notion revived in an 

 overgrown shape. Sir Charles Lyell is no advocate of the theory 

 that lake-basins have been scooped out by huge glaciers ; and in the 

 works we have mentioned he has fully stated the objections which 

 appear to him to render it improbable. He admits, of course, that 

 " heavy masses of ice creeping for ages over a surface of dry land 

 . . . must often, by their grinding action, produce depressions 

 in consequence of the different degrees of resistance offered by rocks 

 of unequal hardness; " but the objections to any long continuance 

 of this scooping action on any particular spot are the greater the 

 larger and deeper the lake-basin to be accounted for, because to 

 excavate such a depression a power is required " capable of acting 

 with a considerable degree of uniformity on masses of varying 

 powers of resistance." In opposition to the view that the great 

 Swiss and Italian lake-basins were scooped out by glaciers Sir 



* ' Antiquity of Man,' p. 309. 



