IRE VILE VS: 
United States Geologic Atlas, Folio 42, Bidwell Bar, California. 
1898. 
This folio consists of six pages of text, signed by H. W. Turner, 
geologist, a topographic map of the district, a map showing the areal 
geology, and a map showing the economic features, with one page of 
special illustrations. The quadrangle represented in this folio lies 
between the parallels 39° 30’ and 4o~° north latitude and 121° 30’ 
and 121° west longitude. It comprises a portion of the northern 
Sierra Nevada and lies chiefly in Plumas and Butte counties. Except 
a small area in the southwest corner, the quadrangle is drained entirely 
by the Feather River. As in the other Gold Belt folios, the formations 
are divided into two main groups: ‘The Bed Rock series, and the 
Superjacent series. 
Bed Rock sertes.— In this quadrangle the Bed Rock series is com- 
prised very largly of old igneous rocks with minor amounts of 
Paleozic sediments. In the northeast corner a single belt of slates, 
known to be of Juratrias age, is noted. The age of the Palzozoic 
rocks is known to be in part Carboniferous. In the Diadem lode there 
occur silicified tests of foraminifera, Zoftusia columbiana Dawson, this 
being the first time this fossil has been found in California. Its age 
is Carboniferous. Other Carboniferous fossils were found at other 
points in the Calaveras formation. The igneous rocks belonging to 
the Bed Rock series may be grouped under three main headings : 
1. Amphibolite and amphibolite schists, diorite and porphyrite. 
In all of the rocks of this series, excepting some of the porphyrite, 
there is a large amount of green aluminous amphibole. The main 
mass of the rocks of this group are metamorphic lavas and tuffs. 
2. Magnesian rocks, comprising serpentine, talc, chlorite and color- 
less amphibole rocks, all of which appear to be merely different altera- 
tion products of rocks of the peridotite and pyroxenite family. The 
serpentine has resulted from the alteration of facies of the magma rich 
in Olivine and rhombic pyroxene, and the talc, chlorite and colorless 
amphibole schists from other facies rich in aluminous pyroxene. ‘The 
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