The Term Sierran,—Hershey. 93 
ing the accumulation of the Auriferous gravels proper. When 
the vulcanism ceased, degradation overcame aggradation and 
the extensive removal of the andesyte and basalt covering and 
erosion of the decayed upper portion of the older rocks to 
form the present rolling uplands may have occurred without 
further uplift. The earlier epoch of erosion is not sharply 
delimited from the later stages of the vulcanism. 
The Auriferous gravels proper have long been correlated 
with the Ione formation in the great valley and considered 
of Miocene age, but the latest work of Merriam, Knowlton 
and others seems to place at least their upper portion in the 
Early Pliocene. The succeeding andesyte and basalt volcanic 
epochs were probably contemporaneous in a general way with 
the extensive Middle Pliocene vulcanism in the Coast Range 
region. This would bring the earlier stages of the post-vol- 
canic erosion in the Late Pliocene and open the Pleistocene 
with the great uplift which inaugurated the canon cutting. 
This view seems to have been held by most students of Sierra 
Nevada geomorphology. 
The correlation of the Sierran cafion with the Ozarkian 
canon valleys of the eastern states is based on the assumption 
that the great Sierra Nevada uplift was virtually contempo- 
raneous with the post-Lafayette uplift which inaugurated the 
Pleistocene in the Mississippi basin, a proposition which has 
not yet been proved and, until the intervening interior basin, 
Rocky mountains and great plains have been more thoroughly 
studied as to their Pleistocene history, it must remain conjec- 
tural. I am averse to correlating erosion cycles on opposite 
sides of the continent. Earth movements in the Pacific Coast 
country have been of such different character from those which 
affected the region east of the great plains that it is far 
from certain that they were parts of the same crustal disturb- 
ances. 
The Sierran valleys—narrow, steep-sided gorges, 1,000 to 
over 3,000 feet in depth, trenched into quite resistant forma- 
tions—cannot be directly compared with the Ozarkian valleys 
of the Mississippi basin, which are much shallower, relatively 
wider, but excavated in softer formations. Taking into con- 
sideration the difference in conditions under which the erosion 
was affected, we may easily reconcile the contrasts and refer 
