——— — * 
The Term Sierran.—Hershey. gi 
The peneplain was virtually completed by the close of 
deposition of the Aurifeous gravels proper and the rhyolyte 
tuff, and was then buried under the andesyte tuff which, after 
filling the shallow valleys, spread out over the uplands and 
pretty thoroughly mantled the surface of the northern half 
of the province. Small monadnocks were widely scattered 
over the peneplain, but those of sufficient size to be promi- 
nent objects in the scenery were not numerous. Probably 
a mountain 150 feet in hight was an important elevation. 
The Bear mountains in Calaveras county are regarded as 
monadnocks and a line of less elevation ike character 
extends northward next to the great va ost as far 
as Oroville. Another important group ng the sum- 
mit north of the Central Pacific railwa = Qn the readily 
pretty thoroughly base-leveled. 7 
The obliteration of the old valley systet se the 
rapid accumulation of the andesyte tuff left the streams free 
to choose new courses. At some time folloy 
opment of the tuff plain, a rather sudden 
province toward the great valley inaugurat 
consequent drainage of the northern Sierras 
elevation the streams were rejuvenated, began 
leys and practically all of the rugged scenery, of this won- 
derful mountain region is their work. 
We now come to an important problem, 
which does not seem to have been made in @ satisfactory 
manner, and which has a direct bearing on th question at 
issue. We have the product of the post-and@syte erosion 
in the form of two strongly contrasted types, the rolling up- 
lands and the cafions. Do they indicate that the uplift was 
affected in two principal stages, of which the first was the 
longer but the amount less, while the second was the pro- 
found orographic disturbance to which the deep cafions are 
due? 
It is possible that the contrast between the rolling up- 
lands and the cafions may be in part explained by a great 
difference in the resistant properties of the material exca- 
vated. During the development of the peneplain, oxidation 
solution of 
