MOHAWK LAKE DEDS. 
401 
the “ Old River Beds of California ” (XII). His conclusions 
in brief are that the enormous deposits of coarse sediments 
(the auriferous gravels) were caused by overloaded waters, 
which resulted from the melting of snow and ice, from the 
heat of the approaching interior lava which soon after was 
erupted, completely filling up the old river beds and causing 
their streams to seek new channels. 
Glacial conditions are presumed to have commenced be¬ 
fore the lava flows and to have reached their maximum after 
the lava flows. It is thought probable that the gradual 
elevation and the attendant glacial conditions commenced 
and advanced until the former culminated in the fracture 
and outflow of lava. He considers that there is a certain 
definite relation between slope and the amount of detritus 
which determines the depth of canons. 
If this relation be disturbed by increase of slope the stream 
will strive to re-establish it. Thus it has been with the great 
canons of the plateau region, and thus it must have been 
with the canons of the Sierra Nevada. Professor Le Conte 
says: 
“ It is difficult to imagine that the Tertiary river channels 
should have remained so shallow after the erosion of the 
whole Cretaceous and Tertiary times if the general Sierra 
slope were as high then as it is now , viz., 100 to 200 feet per 
mile. * * * 
“ The elevation which I suppose took place in the Sierra 
range at the time of the lava flow was evidently of a gentle 
kind, unaccompanied with crumblings and dislocations of 
the strata, and therefore undetectable except by the work of 
canon cutting.” 
In reviewing Whitney’s “ Climatic Changes ” (XVIII), in 
1883, Mr. Gilbert (V, page 194) writes: 
“ If the inclination of the western flank of the Sierra was 
exceedingly gentle in Pliocene time, it would be natural for 
its streams to form deposits on the lower slopes ; and if after¬ 
ward an elevation occurred, increasing this inclination, the 
51—Bull. Phil. Soc., Wash., Vol. 11. 
