50 
Pole, which had hitherto prevented the excessive cooling around 
the poles, and thereby made possible the beginning of the Ice 
Age in America. There were still vast bodies of ocean water at 
the north, but the lack of opportunity for the rapid intermingling 
of those waters with the ocean currents of the south, resulted in a 
glaciers throughout Montana and Idaho, and smaller ones 
throughout the mountains of Utah, Nevada, and Colorado. 
lakes called Lahontan and Bonneville, of which Pyramid and 
Walker Lake and Carson Sirk now represent the one, and Great 
Salt Lake the other. 
\s the access of the ocean currents to the North Pole was still 
farther cut off and the Arctic lands emerged from the sea, and the 
the temperate plants crept up along the valleys of Arizona, climb- 
ing the mountains and the rim of the Great Basin, and slowly 
displaced the dying vegetation of the Frigid invaders, tii! it spread 
out over all the valleys and possessed the land from the Colorado 
to the Yukon, and as the climate still grew milder, the temperate 
a 
