284 GEOLOGY. 
small geological map of the Pass and in the sections. This rock will make excellent lime, but 
there is not a great abundance of fuel in the vicinity. 
Cajon Pass.—A large number of boulders and fragments of white limestone were seen in the 
higher parts of the Cajon Pass, and a considerable body of the rock undoubtedly exists, in situ, 
in some of the adjacent ridges. 
San Bernardino.— This settlement is well supplied with limestone from the mountains south- 
east of the city. I had no opportunity to visit the locality. " 
San Bernardino or San Gorgoso Pass.—Limestone is abundant in almost every point that 
extends outwards from San Gorgoño Mountain towards the west. It is also found in the lower 
ridges along the Desert, near the Pass. 
BITUMEN. 
There are numerous places in the Coast Mountains, south of San Francisco, where bitumen 
exudes from the ground and spreads in great quantities over the surface. These places are 
known as Tar Springs, and are most numerous in the vicinity of Los Angeles. It is also 
common to meet with large quantities of this materialfloating on the Pacific, west of Los 
Angeles, and northward towards Point Conception. I have seen it, when passing this point, 
floating about in large black sheets and masses. These masses are probably the product of . 
submarine springs; or they may be floated down by small streams from the interior. I am 
informed by Lieutenant W. P. Trowbridge, of the United States Engineer Corps, that the 
channel between Santa Barbara and the Islands is sometimes covered with a film of mineral 
oil, giving the beautiful prismatic hues that are produced when oil is poured on water. 
Springs at Los Angeles."—Some of the springs that I examined near Los Angeles were mere 
overflows of bitumen, or asphalt, from a small aperture, around which it had spread out so a8 
to cover a circular space about thirty feet in diameter. This had hardened by exposure, and 
was covered and mingled with dust and sand, which quickly adheres to the clean and fluid 
surfaces. The outer portions were as hard as a pavement, and the mass was highest towards 
the centre, where it was soft and fluid like melted pitch. It was thus evident that all the hard 
portions had risen in a fluid state, and by the heat of the sun had been gradually spread out 
over the surface. Being constantly exposed to dust, which had become thoroughly incorporated 
with the asphalt, it had acquired the consistency and hardness of an artificial mixture. This 
spring is about seven miles from Los Angeles, on the banks of a small brook, and is underlaid 
by bituminous shales. Bituminous shales are also exposed at the shores of San Pedro, near 
the base of the vertical bluffs of the sedimentary formations of the slope. Rounded masses of 
silicious strata, charged with bitumen, are.cast up by the waves, and are probably broken from 
submarine outcrops, -" 
1844). 
h the earth 
bubbles. According to the warmth of the air, the gas contained in the bubbles expands and bursts, producing a rà 
detonation. The inhabitants collect the solidified asphaltu d use it for covering the roofs of their houses, formed of reeds " 
of pieces of wood (shingles). Vessels carry this bitumen to different parts of the coast. This material, nevertheless, — : 
inconvenience of melting in the sun, running down from the roofs, and penetrating through the roofing. The ho i es 
are covered with it require particular care, but small expense, since the springs are worked by any one, according to the 
wants.” 
