388 THE JOURNAL OF GEOLOGY, 
Milton series, and the area in the southern part of the Sierra at 
Mineral King is probably Triassic in age. Under granite, which 
forms much the larger part of the range, are included the pot- 
ash-poor granite or granodiorite of Becker, or tonalite of Vom 
Rath, and the porphyritic granite,’ described in the Fourteenth 
Annual Report, United States Geological Survey. Nearly all 
the small areas noted on the map enclosed in schists or in basic 
igneous rocks are granodiorite, the porphyritic granite occurring 
chiefly along the crest of the range, especially in its southern 
part. The Magnesian series comprises serpentine, talc and 
tremolite schists with some other associated amphibolitic schists, 
the entire series being derived from basic igneous rocks. The 
porphyrites and amphibolitic rocks comprise the rocks laid down 
on the Gold Belt maps as diabase and porphyrite and amphibo- 
lite-schist derived therefrom, and altered igneous rocks which 
are now diorites, and which may be designated, following Cross, 
metadiorites, that is to say, diorites formed from other rocks 
by metamorphism without reference to the character Of mene 
original rocks. The material first determined by Wadsworth? 
as diabase-tufa forms a part of this series. There is, however, 
very little true diabase in the range, while porphyrites (altered 
andesites) on the other hand are abundant. The bisilicate that 
is most common in the porphyrite is augite, but large masses 
contain augite in very subordinate amount. Certain very basic 
portions of these areas seem to have contained olivine and are 
probably melaphyres. The silica contents of the series ranges 
from 48.86 per cent. in the melaphyre-like rocks to 68.56 per 
cent. in the porphyrites with metasilicates in small amount, and 
in some areas the acid porphyries grade over into still more acid 
varieties containing free quartz, as in the rocks of the Gopher 
Ridge. (See Jackson geologic folio.) The amphibolitic schists 
included within the porphyrite and amphibolite areas were © 
«This porphyritic granite was wrongly designated a granite-porphyry in the Four- 
teenth Annual Report, U. S. Geological Survey and in the American Geologist, Vol. 
XIIL., p. 305. A similar use of the term may however be found in Hatch’s Petrol- 
ogy, 1892, p. 114. 
2 Auriferous Gravels, p. 44. 
