Reports of explorations and surveys, to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean: Vol. 5, Pt. 2

GEOLOGY.
POST-PLIOCENE DEPOSITS OF MONTEREY, SAN PEDRO, AND SAN DIEGO.
Evidences of a comparatively recent or Post-Tertiary elevation of the California coast are
found at various points from San Francisco south to San Diego. At San Pedro, near the mouth
of the Los Angeles River, a low bluff, or bank, about thirty feet high, consists of beach-sand
and shingle, mingled with shells, similar to those now living in the waters of the Pacific.
Accumulations of the same kind are also found at Santa Barbara and San Diego.
The bank at San Pedro is composed, at the base, of coarse, brown sea-sand, interstratified with
fragments of shells; but the upper portions are formed of coarser materials, in two or three
layers, from four to six feet thick. The upper layer is of soil and sand, charged with fragments
of Pecten; below this, a thick stratum of sand is filled with shells and a layer of fragments of
a calcareous rock, or soft limestone, perforated in every direction by boring mollusks. Beachshingle and sand, with shells, are found below. These fossils were all remarkably well preserved; but had evidently been subjected to much wearing upon a beach, as the fragments were
very abundant, and many of the shells were broken.
The following species were obtained: Tellina Pedroana, Venerupis cycladiformqs, Saxicava
abrupta, Petricola Pedroana, Sc7hizothoerus Nuttalli, Mytilus Pedroanus, Penitella speleeum,
Fissurella crenulata, Nasga interstriata, N. Pedroana, Strephona Pedroana, Littorina Pedroana. These were all determined and described by Mr. Conrad, who observes in his
letter that " the shells are generally those which live in the adjacent waters, and indicate
little, if any, change of temperature since their deposition. The littoral character of this formation is very evident. Water-worn shells and fragments show the action of the surf, whilst
entire specimens of bivalves, and P.l oladidce, and S'axicave, remaining undisturbed in their selfexcavated domicils, exhibit the same disposition of marine shells that is familiar to the observer
on all sandy and argillaceous shores. They burrow in clay, mud, or sand, beyond the ordinary
action of the surf; whilst some are scooped out by the tempest-driven surge, and others preyed
upon by fishes and marine animals of various kinds, and are thus broken up and deposited
among the living species."
The action of the surf at the base of this bank has liberated great numbers of the fossils, and
they are to be found strewed along the beach, mingled with shells recently cast up by the waves.
A tooth of the mammoth was also obtained from this bank by a brother of Captain Ord, of
TOOTH OF THE MAMMOTH, (lower molar, one-third natural size.)
the United States Coast Survey. It is a lower molar, weighing eight pounds, and twelve inches
long. It has a grinding surface five and a half inches long, which exposes the ends of eight
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