14^ The American Geologist. ^^^'^^^^ ^^os. 
From the size of the gorge below the Nash mine, it appears 
that the glacial deposit at the Nash mine to too old to be con- 
sidered of Wisconsin age (the "Glacial Epoch" of California 
classification). It is certainly not as old as the Kansan epoch, 
but I am not equally positive that it is not as old as the Illinoian 
epoch. The same phenomena that I have described, if situated 
in the Mississippi basin, would indicate the Illinoian epoch. 
However, making allowance for, we will suppose, severer con- 
ditions in this mountain icgion, I will select the lowan epoch as 
the most probable age of liies^ deposits. At the same time I 
will not assert positively that their deposition was not as recent 
even as the Early Wisconsin. In such a mountain valley as 
this, we are dealing with dififerent conditions than in the 
Mississippi basin, and the standards to which I have been 
accustomed have to be used with great caution. The inception 
of the idea that we have here glacial deposits older than the 
Wisconsin has been so recent to me and so opposes a favorite 
theory of mine, that I do not yet feel free to subscribe to it 
without reservations. 
Mr. H. W. Turner='= encountered apparent glacial deposits 
in the Sierra Nevada region far below those usually correlated 
with the Wisconsin drift sheet of the eastern states. Tiiey 
occupy positions which seem to suggest considerable erosion 
between their accumulation and that of the glacial deposits 
near the summit of the range. I have understood Mr. Turner 
to refer them to the time of the earlier series of Wisconsin 
moraines in the eastern states, but it is possible that they date 
from an even earlier epoch. Reviewing Mr. Turner's re- 
marks on them, I should say that they are at least lowan and 
possibly Illinoian in age. The dual history of the great extinct 
Quaternary lakes of the Great Basin region leads us to expect 
evidence of two cold moist periods in the neighboring moun- 
tains, and as the second maximum stage of the lakes was con- 
temporaneous with the glaciation whose efifects are so glaring- 
ly apparent, the earlier maximum stage may be tentatively 
correlated with the older glacial deposits observed b}^ Turner 
and with the apparent older glacial phenomena discussed in 
this paper. 
* "The Pleistocene Geology of the South Central Sierra Nevada with espec- 
ial reference to the Origin of Yosemite Valley." Proc. Cal. Acad. Sci., Third 
Series, vol. i, No. 9. 
