MOHAWK LAKE BEDS. 
391 
with a little lignite and carbonaceous shale, and at one point 
where some sulphur springs issue forth the very fine-grained 
layers contain numerous well-preserved leaves, mostly of 
deciduous trees. Professor Ward has made a preliminary 
examination of these leaves and identifies two forms as 
Quercus distinda and Liquidambar Califomica .* Some of the 
leaves are probably new. In the summer of 1890 I obtained 
here impressions of a bunch of pine leaves and of a winged 
maple seed. Professor Ward considers the plant remains to 
indicate that the beds are about of the same horizon as the 
auriferous gravels, apparently meaning the later and more 
abundant gravels which occur in considerable amount on 
the western slope of the Sierra Nevada, and which seem to 
be but little older than the volcanic material that usually 
covers them. These later and more abundant gravels are 
generally considered of Pliocene age. The Sierra Nevada 
has undoubtedly been a land mass since, at least, early Cre¬ 
taceous time (since the post-Mariposa upheaval). It is there¬ 
fore extremely probable that some of the river gravels of the 
Sierra were deposited by streams that flowed in early Ter¬ 
tiary or even late Cretaceous times. 
For positive evidence of there being older river channels, 
which in some cases are intersected by later channels, the 
reader is referred to R. E. Browne’s paper on “Ancient River 
Beds ” (II), which will be again mentioned further on. The 
beds above described containing the fossil leaves have a 
westerly dip varying from 5° to 30° and are distinctly over¬ 
laid by andesitic breccia. 
I am inclined to correlate the horizontal beds containing 
carbonaceous shale at Mohawk Post Office and Grey Eagle 
Creek, previously described, with the certainly pre-andesitic 
beds, but I have been unable to find any barrier that existed 
before the time of the andesitic eruptions that could have 
* In his “ Report on the Fossil Plants of the Auriferous Gravels of the 
Sierra Nevada,” Memoirs Museum Comp. Zool., Vol. VI, No. 2, Pro¬ 
fessor Lesquereux describes these two species from Chalk Bluffs, Nevada 
county, referring the beds to the Pliocene. 
