THE " GREAT ICE AGE." 139 



cade pouring down a " moulin" a well bored by themselves 

 and reaching the bottom of the glacier. Now what must 

 be the action of such a downflow of water upon my sup- 

 posed submarine bed of till just grazing the bottom of the 

 glacier? Obviously, to wash away the fine clayey particles, 

 and leave behind the coarser sand or gravel. It must form 

 jusfc such a basin or lenticular cavity as Mr. Geikie de- 

 scribes. The oblong shape of these, their longer axis co- 

 inciding with the general course of the glacier, would be 

 produced by the onward progress of the moulin. The ac- 

 cordance of their other features with this explanation will 

 be seen on reading Mr. Geikie's description (pp. 18, 19, 

 etc). 



The general absence of marine animals and their occa- 

 sional exceptional occurrence in the intercalated beds is 

 just what might be expected under the conditions I have 

 sketched. In the gloomy subglacial depths of the sea, 

 drenched with continual supplies of fresh water and cooled 

 below the freezing-point by the action of salt water on the 

 ice, ordinary marine life would be impossible; while, on the 

 other hand, any recession of the glacial limit would restore 

 the conditions of arctic animal life, to be again obliterated 

 with the renewed outward growth of the floating skirts of 

 the inland ice-mantle. 



But I must now refrain from the further discussion of 

 these and other collateral details, but hope to return to 

 them in another paper. 



In "Through Norway with Ladies" I have touched 

 lightly upon some of these, and have more particularly de- 

 scribed some curious and very extensive evidences of sec- 

 ondary glaciation that quite escaped my attention on my 

 first visit, and which, too, have been equally overlooked by 

 other observers. In the above I have endeavored to keep 

 as nearly as possible to the main subject of the origin of the 

 till and the character of the ancient ice-sheet. 



