Los Angeles herald., 1910-09-25

able for the deposition of coarse sedi-
ments. During q part of the eocene
there was a recession of the sea from
portions of both the San Joaquin and
Sacramento valleys, and the RECORDS
left I'm the strata show that marshland
or fresh water conditions prevaiied, IN
the deposits formed during this time
are to be found some workable coal
beds.
CALIFORNIA ONCE DRY
Following the eocene came a period
of uplift, when practically all of Cali
fornia was dry land and was subjected
to erosion. This period is called the
oligocene. Only a small area in the
Santa Cruz mountains Is known to
have been submerged during this pc
riod, though II is possible that por-
ton of the lower end of the San Joa-
uuin may still have been connected
with the sea through a narrow strait
near Ventura.
Just following the oligocene and dur
ing the early part of the miooene came
some of the most important earth
movements in the southern coast
ranges. All of the San joaquin valley
and the coast ranges from San Fran
cisco to Los Angeles were again low
cred below the sea, except for rev
islands. where the mountains now ex-
ist. During the subsistence of the San
JOAQUIN, the Sacramento valley re-
mained above the sea level and did not
share the great earth movements with
the San JOAQUIN. This condition of the
| Sacramento continued during the mid
die portion of the miocene, when the
great thickness of diatomaceous Shales
was being deposited In the region south
| out San Francisco bay North OF the
bay narrow necks were submerged and
we find isolated deposits of diato-
maceous shale at Point Reyes and at
! Point Arena. OF the territory which
was submerged during the early mio-
Gene, a large portion gradually sub
sided more during the middle mlocene
| time, allowing a deposition of great
| thickness of deposits. During Monterey
| time 1t is probable that erosion was
not very active, as the deposits of the
age are chiefly limestones and diato-
maceous shales, the latter predominant
| ing. The sea conditions which must
have existed during that time can be
seen at the present time, as In some
! localities the dlatom plants thrive IN
| such abundance as to accumulate
deposit on the sea bottom very rapidly
FOLDS AND FAULTS
Following the Monterey came an
| other gread period of readjustment,
which consisted of intense folding and
| faulting, and in many localities the
uplift was extremely great and the
| erosion very active. Later a further
subsistence took place, which was prob
ably the most profound in the tertiary.
| Almost the entire coast range south OF
| San Francisco bay and a large portion
| adjacent to the ocean north of the bay
were submerged and a considerable
thickness of deposits formed, During
| a part of this time the conditions for
the deposition of diatomaceous shales
was favorable and we find such de-
posits in the southern coast ranges.
1.-THE deposits of such shales did not
reach a great thickness, but in some
localities it is probably the source of
petroleum. During this period por-
| ton of the Sacramento was probably
! submerged under the inland sea, but
the deposits over the greater part of
| the valley indicate the water was fresh
| or brackish.
Following the upper miocene, in the
| pleocene period, we find the coast
ranges again uplifted and the sea prob
ably entirely cut off from the interior
valleys, as the great thickness of sed-
| iments in the San joaquin are of fresh
water origin. Only a limited amount
| of territory adjacent to the coast was
under the sea. The Sacramento Valley