288 The American Geologist. May, 1902. 
outcrops to the south. We have then three east-west belts of 
limestone separated by two anticlinal belts of quartzyte. “Mar- 
ble mountain,” mapped about fifteen miles east of Oro Grande 
is probably a part of this same series. 
This combination of pure quartzyte overlaid by nearly pure 
limestone with virtually no formation of schists or slates is an 
unusual one for California, but is an association common in 
the Rocky Mountain and Black Hills region. The alteration of 
the Oro Grande series has destroyed all fossils and its age can 
only be conjectured, although in this case such conjecture may 
have a very strong basis. Except for a higher degree of met- 
amorphism, it is identical in character with the Lower Cam- 
brian series described by Walcott* from Inyo county and I be- 
lieve the propriety of classing it as Lower Cambrian will 
hardly be questioned. 
The relation between the Oro Grande series and the gneiss- 
schist series near Barstow is not proved, but it is safe to say 
that the former is newer than and rests on the latter. The 
Oro Grande Lower Cambrian series shows regional metamor- 
phism. Its appearance indicates a slightly less age than the 
Klamath and Pelona Schist series, but a somewhat greater 
age than the Devono-Carboniferous of the Klamath and Sierra 
Nevada regions. The occurrence of this Lower Cambrian 
series so near to the Pelona schists but less highly metamor- 
phosed than the latter seems to me to corroborate other evi- 
dence of the pre-Cambrian age of the Pelora and indirectly 
of the Klamath Schist series. 
At mile-post thirty-two and one-half from Barstow toward 
San Bernardino, the railroad touches a line of outcrop of a 
fine-grained schistose rock which weathers to a dark color. A 
band of it several hundred feet wide extends northeast along 
the border of the Mesozoic granite to well up the slope of a 
high quartzyte mountain whose southern flank the granite 
reaches. I consider the dark band a zone of contact-meta- 
morphism in the quartzyte due to the intrusive granite. It 
is properly a quartz schist, The less degree of alteration af- 
fecting the series uniformly over many square miles and far 
distant from any intrusive granite is pre-Mesozoic. 
*Am. Jour. Sci., vol. xlix, March, 1895, p, 141. 
