406 LTT Af OO KEIN ALE OTN GLH OLE OG Nea 
the rhyolite-flows is shown by the plant remains occurring chiefly 
in clay beds of the Neocene Auriferous gravels with which the 
rhyolitic material is associated. Some of these clays have been 
thought themselves to be decomposed rhyolitic material. These 
plant remains, chiefly leaves, have been studied by Lesquereux, 
Ward, and Knowlton. Professor Lesquereux, it is true,’ first 
considered the plants from the Auriferous gravels to indicate a 
Pliocene age for the containing beds, but in a more recent report? 
he refers other plants from the same, or possibly a somewhat 
later horizon, to the Miocene.3 
Analyses of two rhyolites are given in the table (Nos. 126 
Amador county, and 365 Plumas county). A number of partial 
analyses have been made of rhyolites from other localities, and 
all show a remarkably uniform silica, lime, soda, and potash 
ratio. 
In Butte and Plumas counties there are extensive tables of a 
dense fine-grained black basalt, represented in the table of anal- 
yses by No. 276 Plumas county, and No. 18 Sierra Nevada. 
At many points the tables of this basalt are capped with andesite- 
breccia, showing that it is earlier than the andesite. Its age rel- 
ative to the rhyolite is not known to the writer, but it is thought 
to be later, since the gravels which it covers at some points 
appear to belong to later channels than those covered by the 
rhyolite. Still, at Sawpit, northwest of Onion Valley (Downie- 
ville atlas sheet), this older basalt covers the older white quartz 
gravels, and on the Oroville Table Mountain it caps the Ione 
formation. 
After the rhyolite and older basalt flows there was a period 
of erosion before the main andesite eruptions. These were of 
hornblende-pyroxene-andesite, an analysis of an average sample 
of which is given in the table (No. 72 Sierra Nevada collection). 
Much of the andesite occurs in the form of a tuff or breccia, and 
"Memoirs Museum of Comp. Zool., Vol. VI., No. 2, p. 54. 
2J.S. Diver, Eighth An. Rep. U.S. Geol. Survey, p. 419. 
3 The age of the Auriferous gravels is discussed in a paper by DILLER (JOURNAL 
GEoLoGy, Vol. II., pp. 32-54) and in a paper by the writer to appear in the American 
Geologist, June 1895. 
