54 
GEOLOGY. 
of this rock, the lines being very near together and generally of different colors. It is com¬ 
pact and porphyritic ; the crystals disseminated in it being small and white, resembling feld¬ 
spar. 
After passing this ridge, we travelled for several miles on the surface of the dry lake which 
was visible from the Tejon pass. This consists of a perfectly level and floor-like bed of clay, so 
hard that the mules left scarcely any tracks upon it. It extended for miles ; and the pellicle 
upon the surface being exceedingly fine and polished the distant portions appeared like water, 
and the mountains and other objects were reflected as if from a mirror. It reminded me of the 
frozen surface of a lake. 
At the further extremity of this dry lake, or on the margin of its widest portion—for it 
appeared to he prolonged further east and north—we reached another series of lost ridges. As 
we approached them, the ground was found to he strewn with a pink gravel, which consisted ot 
angular fragments of feldspar of that color, and indicated that the ridges were granitic. This 
was found to be the case, the rock being a gray granite, traversed by large veins or masses of 
pink feldspar, or granitic veins, in which this feldspar was the predominating constituent. 
These veins were so large and numerous in some places that they could easily he mistaken for 
the principal rock of the ridge. Their direction appeared to he variable : one had a trend of 
N. 36° W.; a second, N. 14° B.; and a third, N. 66° E. TLe granite which is cut by these 
veins has an even texture, and contains a large amount of feldspar ; it decomposes into gran- 
xilar masses, which may he crumbled in the hand. Numerous little peaks were formed by the 
projection of limited exposures of granite above the general surface of the Basin, and a corre¬ 
sponding number of little valleys or basins was inclosed by them ; so that the general character 
of the surface of the Great Basin was represented in miniature. We traversed a considerable 
area among these outcrops of granite, and occasionally found large blocks of it standing out 
upon the surface, the surrounding rock being covered from sight by a thin layer of feldspathic 
gravel. One of the highest points that we reached presented an almost vertical bluff, five or 
six hundred feet high towards the north, and was surrounded on all sides by a regular slope. 
This being the most elevated point in that vicinity, we had a fine view of the surrounding 
country. On the south, at a distance of twenty-five or thirty miles, we could see the blue 
summits of the transverse chain of mountains forming the southern boundary of the Basin ; 
and on the west the lofty ridges of the Sierra Nevada—the intervening country being a treeless 
desert. Towards the north the eye could roam among countless lost mountains rising like the 
waves of the ocean in a storm, presenting a constant succession of peaks, until, by their number, 
they appeared to form a continuous range. 
Several peaks, at a distance of forty or fifty miles, had a peculiar conical form, having flat¬ 
tened tops, suggestive of volcanoes, hut there was no opportunity of verifying such a supposition. 
They may be the remnants of elevated plains of sedimentary origin, or of overflows of lava or 
basalt. 
We returned from this point towards the first spring, nearest the Tejon Pass, and on the way 
hack found one or two additional hut smaller springs, one of them on the border of the dry 
lake at the base of the bluff of porphyritic rocks. 
October 13.—We left the spring, and, instead of following our trail back to the Tejon Pass, 
struck across the plain of the Basin, in a southerly direction, towards the entrance of the Pass 
of San Francisquito. This is in the chain of mountains extending a little south of east from 
the Sierra Nevada to the peak of San Bernardino, at the source of the Mojave river. This chain 
