California Tertiary Formations.—Hershey. 307 
sandstone near Gorman’s station. The borax mines west of 
Fraser mountain seem to be in connection with another patch 
of them. Probably many other isolated areas will be found 
in the southern Coast ranges. 
The Rosamond belt swings around the western end of a 
broad low undulating granite belt and then starts east again. 
Three miles south of Mojave is the Exposed Treasure mine 
and a lot of other prospects on a low mountain, very rocky 
and showing colors of black, yellow and light brown. The 
hill has a base of granite and over this is a massive, very coarse 
textured, porphyritic rhyolyte. Associated with and perhaps 
over this is an ordinary white rhyolyte of massive structure. 
A black stain on the rhyolyte where exposed gives the black 
color to much of the surface of the hill. 
Soledad peak, four miles south of Mojave, is the highest 
and by far most prominent of the rhyolyte hills of this region. 
It rises to 1200 feet above the plain and shows the dark 
red, purple, yellow, light green, etc., of most of the rhyolyte 
hills. The material of a rather dark spur has the macroscopic 
appearance of andesyte, but under a hand microscope appears 
quite acid. Similar material externally resembling andesyte of 
reddish color occurs in many of the hills near the Santa Fe 
railway, 5 to 7 miles southeast of Mojave, but most of it out- 
crops like rhyolyte and seems too acid for an andesyte. Doubt- 
lessly some interesting discoveries here await the petro- 
grapher. 
I traced the lava belt eastward by means of a line of 
buttes showing the characteristic colors and topography of the 
Rosamond series, checking occasionally by a close examination. 
It is in the form of a narrow strip, rarely over several miles 
wide, trending easterly, across Mohave desert and probably 
marking a line of fissures in the granite. A prominent group 
several miles north.of Rogers dry lake-bed includes Castle and 
Desert buttes, old land-marks. If the detrital slopes were re- 
moved, the rhyolyte belt would probably be continuous to a 
point about five miles northwest of Kramer. Then there is 
an interruption for several miles, after which the rhyolyte 
sets in stronger than ever and forms a high rugged, purple 
and yellow range trending far to the eastward, not many miles 
north of the railroad. From Hinkley station eastward the 
