6 GEOLOGY. 
from San Francisco and the ocean, near the Golden Gate. This mountain is considered 
volcanic by many in California, but no evidence of it has yet been seen. 
Our second camp was in a grove of oaks on the bank of a small brook. Here a slight dew 
fell during the night. Temperature of the air at sundown, 74°; at 9 p. m. 64? 
The narrow valley in which we had been travelling gradually expanded, and at one place 
reached nearly to the foot of Mount Diablo, forming a plain of considerable extent. This was 
timbered near the hills and the mountain by a growth of evergreen oaks mingled with the 
common ‘white oak’’ of California, (Quercus Hindsii.) 
The general appearance of this valley or plain, with Mount Diablo beyond, is doma i in the 
outline engraving. The foot hills are almost devoid of trees, and present singularly rounded 
outlines. They are covered with the dead stalks of the wild-oat. - 
An outerop of coarse-grained sandstone was seen near the border of the valley. The rock 
contained large pebbles, most of them as large as hens’ eggs, and similar to those collected at 
Benicia. 
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MOUNT DIABLO AND DIABLO VALLEY. 
About three miles beyond the camp, July 12th, another outcrop of a conglomerate was 
found, trending about north 30? west. From this place high hills of stratified rocks were 
visible at the foot of Mount Diablo. Two miles beyond, and near the banks of a small stream, 
which we followed, a succession of sandstone strata were exposed in a bluff about six hundred 
feet long. They were. highly inclined at an angle of 60°, dipping easterly, the trend being 
nearly northwest and southeast. The strata are soft and not firmly consolidated, consisting of 
argillaceous sandstones of different degrees of fineness; some of the beds*being coarse-grained 
and filled with pebbles. The cast of one valve of a shell of the genus Cardium was found on 
the surface of one of the layers, but it was in an imperfect state. 
On approaching Livermore’s valley, or rancho, we left the main road and crossed over low 
hills on the left. Outcrops of soft, earthy sandstones were frequently seen. At one point the 
trend was north 30° west, and the dip northeast, at an angle of 45°. Beyond this a reverse 
dip was found, and, to all appearance, an anticlinal axis. The strata were all light colored 
and contained a large amount of clay, and clay mingled with sand. In one stratum a large 
amount of pumice-stone was found disseminated in irregular masses, from one-quarter of an 
inch to several inches in diameter. It was white and very soft and fibrous, the cells being 
nearly all in one direction and elongated. 
This formation of sandstone and conglomerate, which was so constantly seen, is, apparently, 
