-■tt) The American Geologist. April,i894 
pushed ou1 of their normal northwesterly strike near the granite, in 
places striking east and west. They have, moreover, been converted 
into mica-SChistS, which at some points, as in Yagui gulch', carry small 
andalusite crystals. According to Fairbanks, t he clay slates, one-fbur1 h 
mile from the granite, contain needles of fibrolite.* 
[n the lower foothills of Madera and Mariposa counties is a bell of 
mica-schist, portions of which carry large andalusite crystals in great 
abundance. Attention was called to this schist bell many years ago by 
Prof. Blake. The Xe Plus Ultra and Buchanan copper mines are in 
these schists. This bell may also be a metamorphosed area of .Mariposa 
slates. At Merced Falls, at the \er\ west edge of the foothills on the 
Merced river, is a bell of clay slates, which is probably the southward 
continuati >f the western belt of the Mariposa formation, which ex- 
tends from Folsom through Salt Spring valley southward. The general 
si rike of this bell of clay slates would carry it into the ( Jhowchilla mica- 
andalusite-schisl area. 
The Mariposa slates form an integral pari of the auriferous slate 
series. The dip of the slates is usually from 70° to vertical. At Folsom 
a little west of the bridge over the American river, are nearly horizon- 
tal unaltered sandstones containing Chico fossils; while not far east of 
the bridge are contact mica-schists of the Mariposa formation dip- 
ping at a high angle. No more conspicuous unconformity exists in the 
Sierra Nevada than that between these unaltered Chico strata and the 
neighboring metamorphic schists of the Mariposa formation. The pos- 
sibility suggested by Mr. Dillerf of the upheaval of the Mariposa beds 
having occurred after the Chico, or Miocene beds were deposited, can- 
not he entertained. 
Chico Formation. 
The sediments of the Chico formation where seen in the 
foothills of the Sierra Nevada consist chiefly of sandstone and 
conglomerate. In the areas examined by the writer the dark 
shales that form part of the series in the Coast ranges do not 
appear. These sandstones lie with a marked unconformity 
on the rocks of the auriferous slate series. The beds fre- 
quently have a gentle dip toward the valley. The most south- 
ern locality in the gold belt where the Chico formation is 
known with certainty is at Folsom on the American river, 
where the beds have an altitude of two hundred feet above sea 
level. Prof. Whitney first called attention to this locality. 
From here north Chico beds have been found at various points, 
the altitude increasing with the latitude. At Pentz P. O. in 
Butte county the beds are about 400 feet in elevation; on 
( liico creek 500 feet or more; underlying Shasta valley 2,500 
-Tenth Ann. Rep. State Mineralogist of Cala., p. 30. 
tBull. Geol. Soc. Am., vol. 4, p, 12-. 
