272 THE STORY OP THE EARTH AND MAN. 



familiar, they necessitate the conclusion that in the 

 period of extreme refrigeration, the greater part of 

 the land was under water, and such hills and moun- 

 tains as remained were little Greenlands, covered with 

 ice and sending down glaciers to the sea. In hilly 

 and broken regions, therefore, and especially at con- 

 siderable elevations, we find indications of glacier 

 action; on the great plains, on the contrary, the 

 indications are those of marine glaciation and trans- 

 port. This last statement, I believe, applies to the 

 mountains and plains of Europe and Asia as well as of 

 America. 



This view requires not only the supposition of great 

 refrigeration, but of a great subsidence of the land in 

 the temperate latitudes, with large residual islands 

 and hills in the Arctic regions. That such subsidence 

 actually took place is proved, not only by the frequent 

 occurrence of marine shells in the boulder clay itself, 

 but also by the occurrence of stratified marine 

 clays filled with shells, often of deep-water species, 

 immediately over that deposit. Further, the shells, 

 and also occasional land plants found in these beds, 

 indicate a cold climate and much cold fresh water 

 pouring into the sea from melting ice and snow. In 

 Canada these marine clays have been traced up to 

 elevations of 600 feet, and in Great Britain deposits 

 of this kind occur on one of the mountains of Wales 

 at the height of 1300 feet above the level of the sea. 

 Nor is it to be supposed that this level marks the 

 extreme height of the Post -pliocene waters, for drift 



