IGNEOUS ROCKS OF THE SIERRA NEVADA. 409 
fied trunks of both deciduous and coniferous trees, bowlders of 
granite, some of them tons in weight, and pebbles and fragments 
of nearly all the older rocks of which the Sierra Nevada is com- 
posed, are found imbedded in the andesitic material. 
Along the east side of the Great Valley of California these 
andesite-tuffs grade into well-stratified material containing abun- 
dant rolled sand grains, and such areas may be regarded as water 
deposits. A most remarkable fact has been noted by the writer 
in regard to these tuff areas, and that is that wherever the orig- 
inal top layer of the beds has been preserved this is, so far as 
observed, a distinct breccia, composed chiefly of angular frag- 
ments and blocks cemented by ashes, while below are layers of 
“e\HBL: PYRZANDSBRECCIA . 
ho Xe) Soo 
x 8 reoy 
©0507 /CONGLOMERATE - 
- ee ee ee, 
Fic. 3. Lava-capped hill four miles west of Ione. Elevation about 400 ft. above 
base. 
fine tuff and volcanic conglomerates, The accompanying section 
(Fig. 3) represents the layers composing a flat-topped hill about 
four miles west of Ione, in Amador county. 
With variations as to the layers of conglomerate and tuffs in 
their number and thickness, this section may be verified at a great 
number of points in the foothill region. The andesite of the 
breccia eruptions is a coarse-grained rock. It is shown in the 
table of analyses by No. 72 Sierra Nevada, which came from the 
southwest base of Mt. Ingalls. No. 16 Sierra Nevada is a massive 
occurrence of a similar coarse andesite, but differs from No. 72 
in containing hornblende to the exclusion of pyroxene. 
In the area of the Downieville and Bidwell Bar atlas sheets 
