Geological Survey of the Territories in 1872. 203 
sembles the outline of a well-filled purse. It is apparently quite 
deep; but its depth was not ascertained. From its eastern 
called Lake Lewis, in memory of Capt. Merriwether Lewis, who 
would otherwise be without memorial in the region which he 
was the first to explore, since “ Lewis's Fork” of the Columbia 
has now reverted to its Indian name of Shoshone or Snake 
above Lake Riddle, or 8024 feet above the sea. 
Moving southward from Mt. Sheridan, the region about the 
ultimate sources of the main Snake was pretty thoroughly 
since leaving Tyghee Pass. and found ourselves among fine- 
value. 
The ultimate source of the main stream of the Snake isa 
about 500 feet, shows a face of quartzite gravel reaching to its 
very summit, where the deposit is just pierced by an outcrop 
of the gray trachytic lavas and A basalt, which form the nu- 
cleus of the ridge. This is one of the highest points in the im- 
mediate neighborhood, being about 8654 feet above the sea ; 
and there was nothing to indicate, with any certainty, 
been the source and course of the large river which 
tributed such immense amounts of gravel. Only the general 
levels imply a southern source and a northward flow. Erosion 
has taken place since on so grand a seale that one 1s compelled 
to consider the deposit very ancient. 
