GLACIAL PHENOMENA IN NEVADA 



tion extending over all the valleys now form- 

 ing the sage plains as well as the mountains. 

 The basins of the main valleys alternating 

 with the mountain-ranges, and which contained 

 lakes during at least the closing portion of 

 the Ice Period, were eroded wholly, or in part, 

 from a general elevated tableland, by immense 

 glaciers that flowed north and south to the 

 ocean. The mountains as well as the valleys 

 present abundant evidence of this grand origin. 

 The flanks of all the interior ranges are seen 

 to have been heavily abraded and ground 

 away by the ice acting in a direction parallel 

 with their axes. This action is most strikingly 

 shown upon projecting portions where the 

 pressure has been greatest. These are shorn 

 off in smooth planes and bossy outswelling 

 curves, like the outstanding portions of canon- 

 walls. Moreover, the extremities of the ranges 

 taper out like those of dividing ridges which 

 have been ground away by dividing and con- 

 fluent glaciers. Furthermore, the horizontal 

 sections of separate mountains, standing iso- 

 lated hi the great valleys, are lens-shaped like 

 those of mere rocks that rise hi the channels 

 of ordinary canon glaciers, and which have 

 been overflowed or past-flowed, while hi many 

 of the smaller valleys roches moutonnees occur 

 in great abundance. 



191 



