GLACIAL PHENOMENA IN NEVADA 



Second, this tableland, bounded on the east 

 and west by lofty mountain-ranges, but com- 

 paratively open on the north and south, was 

 loaded with ice, which was discharged to the 

 ocean northward and southward, and in its 

 flow brought most, if not all, the present in- 

 terior ranges and valleys into reUef by erosion. 



Third, as the glacial winter drew near its 

 close the ice vanished from the lower portions 

 of the basin, which then became lakes, into 

 which separate glaciers descended from the 

 moimtains. Then these mountain glaciers van- 

 ished in turn, after sculpturing the ranges 

 into their present condition. 



Fourth, the few immense lakes extending 

 over the lowlands, in the midst of which many 

 of the interior ranges stood as islands, be- 

 came shallow as the ice vanished from the 

 mountains, and separated into many distinct 

 lakes, whose waters no longer reached the 

 ocean. Most of these have disappeared by the 

 filling of their basins with detritus from the 

 mountains, and now form sage plains and "al- 

 kali flats." 



The transition from one to the other of these 

 various conditions was gradual and orderly: 

 first, a nearly simple tableland; then a grand 

 mer de glace shedding its crawhng silver cur- 

 rents to the sea, and becoming gradually more 



193 



