THE GREAT ICE AGE 371 



believe that in the Glacial age the whole continent of North 

 America, as far south as the latitude of 40, was covered with a 

 continuous glacier, having a wide front, and thousands of feet 

 thick, we may well ask, first, what evidence there is that Green- 

 land or even the Antarctic continent is at present in such a 

 condition ; and, secondly, whether there exists a possibility 

 that the interior of a great continent could ever receive so large 

 an amount of precipitation as that required. So far as present 

 knowledge exists, it is certain that the meteorologist and the 

 physicist must answer both questions in the negative. In short, 

 perpetual snow and glaciers must be local, and cannot be con- 

 tinental, because of the vast amount of evaporation and con- 

 densation required. These can only be possible where com- 

 paratively warm seas supply moisture to cold and elevated land, 

 and this supply cannot, in the nature of things, penetrate far 

 inland. The actual condition of interior Asia and interior 

 America in the higher northern latitudes affords positive proof 

 of this. In a state of partial submergence of our northern 

 continents, we can readily imagine glaciation by the combined 

 action of local glaciers and great ice floes ; but in whatever 

 way the phenomena of the boulder clay and of the so-called 

 " terminal moraines " are to be accounted for, the theory of a 

 continuous continental glacier must be given up. 



The great interior plain of western Canada, between the 

 Laurentian axis on the east and the Rocky Mountains on the 

 west, is seven hundred miles in breadth, and is covered with 

 glacial drift, presenting one of the greatest examples of this 

 deposit in the world. Proceeding eastward from the base of 

 the Rocky Mountains, the surface, at first more than 4,000 

 feet above the sea level, descends by successive steps to 2,500 

 feet, and is based on Cretaceous and Laramie rocks, covered 

 with boulder clay and sand, in some places from one hundred 

 to two hundred feet in depth, and filling up pre-existing hollows, 

 though itself sometimes piled into ridges. Near the Rocky 



s. E. 27 



