190 J. LeConte—Old River-beds of California. 
high Sierra was mantled with snow and ice and glaciers proba- 
bly occupied the higher portions of the river troughs, and thus 
g a new system wholly 
independent of the previous one, though having the same gen- 
eral direction. In cutting these new channels the rivers seem 
was the high Sierra ice mantled and all its cafions filled wit 
glaciers, but even the much lower Coast Range was snow-cap- 
ped, and glaciers probably ran down its valleys nearly or quite 
into the Bay of San Francisco.* As another result of the 
increased elevation of the Sierra and the prodigious consequent 
erosion by ice and water of this time, and of water alone 12 
subsequent times, the erupted lava was swept clean away from 
the greater portion of the high Sierra, leaving only the roots 
visible in the form of dikes, and the river channels lower dow? 
the slope were cut far below the detritus-filled and lava-capped 
old river channels, which are thus left high up on the present 
divides. Meanwhile meteoric waters percolating downward 
through the decomposing lava caps, and therefore charged with 
carbonates of soda and lime, and therefore also dissolving silica, 
cemented the gravels and petrified the drift wood, or else tak- 
ing more silica, changed in places volcanic and slate pebbles 
and bed rock into clay. 
Berkeley, Cal., Oct. 15, 1879. i 
* I have found what I regard as good evidence of glacial action about the sil 
of the University, 300 feet above the Bay of San Francisco. 
