480 Proceedings, 



performs its work of eroding the elevated rock mass into ridges and peaks ; 

 and that after the first rough excavation has been performed, and only the 

 hard cores of crystalline or tough metamorphic rocks have survived the 

 denudation, and when the valleys have all been perfectly moulded to perform 

 their functions of ice gutters, then the process is admitted to be very slow. 

 But to ascribe thus to glacier action the formation of the very ridges and 

 peaks of mountain tops is, I think, unreasonable. In fact no larger amount of 

 work can be assigned to glaciers even of the glacial epoch, as the Duke of 

 Argyle remarks in a quotation made by Mr. Travers, than that of deepening 

 the valleys which existed before — that on the one hand when the period 

 began it found the existing system of hills and valleys in the main determined, 

 and on the other that it cannot have left them exactly as it found them. But 

 this is very far from the view which Dr. Hector would seem to maintain — 

 that mountain and valley, with all their characteristic variety of surface, have 

 been cut out of the solid by enormous glaciers. Now, the very opposite is 

 the case. It is the pre-existing configuration of hill and valley and mountain 

 range which has determined the movements of these glaciers, so that, as the 

 Duke of Argyle says, the effects of glacial denudation become a comparatively 

 narrow question. 



But whether we ascribe too much or too little to the existence of a glacial 

 epoch, let us for a moment consider what are the probable causes which might 

 explain the extraordinary changes of climate which have certainly existed in 

 the earth in very distant epochs of time. 



There are two sources of heat which have varied greatly — the heat of the 

 sun and heat from the body of the earth itself. 



Our faculties can form no conception, and can make no answer to the 

 question, how far the forces which are in activity in the sun have exhausted 

 themselves. Say that such changes can be worked out in any length of time 

 that can be assigned ; such period, however vast, is nothing to eternity. To 

 eternity no limit is assignable j priest and philosopher alike are ignorant here. 

 But though we can give no answer to the question, we are assured that the 

 forces which are in activity in the sun as revealed to us by light, " the winged 

 messenger," through the spectroscope, are forces operating on the same sub- 

 stances as those which form the earth ; that they must have had a beginning, 

 as assuredly they will have an end ; and that the sun will in the course of time 

 cease to evolve heat, light, and electricity. It seems certain that they vary 

 greatly in their intensity — at one epoch the heat of the sun may have been 

 much greater than it is now, and at another fiir less. It is impossible they can 

 have always been the same. 



I have dwelt longer on this subject than I should have done, had I not 

 been desirous of introducing to your notice the very plausible theory of 



