178 
GEOLOGY. 
larities are filled up by more modern accumulations. The nearly horizontal position of the 
upper strata of the slope is shown by slight outcrops at several points near the city. 
At one of these outcrops, in the bank of a brook, the strata are argillaceous and sandy shales, 
charged with bitumen, and this substance rises to the surface in the vicinity. At another point 
nearer the city, and among the gently rolling hills just north of it, the strata are white, like 
chalk, and very tough, so that the rock can be broken out in blocks. It is very light and 
porous, absorbing water rapidly when wet, and emitting a strong argillaceous odor. It is 
principally white clay and fine sand, and does not effervesce with acids. It appeared to have 
been quarried, under the supposition that it contained lime. 
At San Pedro, twenty miles distant, there is a fine exposure of the edges of strata in the bluff 
overhanging the beach. This bluff is from forty to sixty feet high, and is nearly vertical, 
being constantly undermined by the waves. The strata appear in nearly horizontal lines along 
the face of the bluff ; and present a considerable difference in their lithological characters. 
Some of them are almost wholly formed of clay, others of soft sandstone, and others of a more 
compact, but fine-grained rock, formed by the mingling of the two materials. With the excep¬ 
tion of some beds at the base of the series, they are all light-colored, and have a modern 
appearance, The lower beds are bituminous, and emit a strong odor of bitumen when they 
are struck by the hammer. This bituminous mass is thinly stratified, and is, in fact, a mass 
of bituminous, clay shales, which are soft and plastic where washed hy the tide. They are 
exposed along the shore, the base of the beds being below the surface of the water, but the upper 
limit rising in places to a height of five feet above it. Above these bituminous shales the 
argillaceous beds are stained with oxide of iron, and nodular masses or concretions of the oxide 
protrude from the face of the bluff at many points. A short distance beyond the landing, the 
upper part of the beach, under the cliff, is strewn with large, tabular blocks of sandstone, of a 
brown color, and evidently derived from the wear of the bank. They lie piled together in con¬ 
siderable quantities, and resist the action of the surf very well. They are thus shown to be 
much harder than the other strata, which are easily washed away. The surfaces of these 
blocks present peculiar markings, or reticulations, which are readily recognized as sun-cracks, 
and are precisely similar in appearance to those found on the slabs of red sandstone in the 
quarries of New Jersey and Connecticut. They also resemble the deep cracks produced in the 
clay soils of California by the sun and air after the rainy season. It would thus appear that at 
the time of the deposition of this stratum of sandstone it was alternately above and below the 
surface of the water, and it may have formed the surface-layer of a shelving beach or estuary 
flat, occasionally left bare and exposed to the sun for a long time. 
Among other fragments of sandstone and igneous rocks along the beach, I procured many 
rounded masses of a black, or brownish-black, silicious rock, which much resembled coal, or a 
dark, impure resin. The lines of stratification were very numerous and near together, and 
some of the fragments cleaved readily, parallel to these layers ; but most of them broke with a 
conchoidal fracture, yielding thin, sharp fragments like flint or obsidian, though not so vitreous. 
These masses were evidently bituminous, and were very interesting as an indication of the 
proximity of strata formed of the same material, for they are probably broken from an outcrop 
below the surface of the water. They are still more interesting from a close resemblance they 
bear to compact vitreous beds in the great infusorial formation of Monterey. The presence of 
strata of marine infusoria in the vicinity of San Pedro is thus indicated. Specimens of this 
