150 
OIL DISTRICTS OF SOUTHERN CALIFORNIA. 
these concretions are round, while at others they vary from elliptical 
to irregular; they are usually 4 feet or less in diameter. In some of 
the layers of this band the grains of quartz and feldspar attain a 
diameter of three-eighths of an inch, in others the grain is finer. 
The color of the sands here varies from gray through light yellow to 
purple, the latter color indicating the former presence of oil in the 
rock. 
About 300 feet stratigraphically beneath the upper oil sands is the 
second productive layer. This consists of 40 to 50 feet of Thick to 
medium-bedded arkose strata, similar in all practical respects to the 
upper sands. Between these two principal layers and in the shale 
beneath the lower are other sandy beds, which are shown by the well 
records in the west end of the field to be more or less productive. 
The great bulk of the oil, however, is derived from the two principal 
layers just described. 
MIOCENE BASALT. 
Large masses .of basalt are associated with the Puente sandstone 
and shale in the region about the mouth of Cahuenga Pass and to the 
east as far as Laughlins Hill. From evidence to be obtained at dif¬ 
ferent localities in this region, both intrusive masses and surface flows 
are represented by the rock. Outcrops of a spheroidal type, such as 
that forming the little knoll three-fourths of a mile northwest of Hol¬ 
lywood, indicate the intrusions, while the vesicular facies found in the 
east end of Laughlins Hill tends to prove the existence of the flows. 
The usual color of the weathered outcrops is purplish red to reddish 
brown, the overlying soil in nearly all cases partaking of the character¬ 
istic color of the underlying rock. The igneous rock in the knoll 
three-fourths of a mile northwest of Hollywood, although doubtless 
genetically identical with the fine-grained basalt lying farther east, 
somewhat resembles in hand specimens certain forms of diabase. 
The age of the basalt is the same as that of similar rocks found north 
and northwest of Santa Monica in the Santa Monica Mountains, also 
in the Puente Hills, north of Brea Canyon, and in many regions of the 
Coast Range at least as far north as the Santa Cruz Mountains. The 
rock intrudes or is interbedded with the Vaqueros sandstone and Mon¬ 
terey shale or contemporaneous formations at one locality or another, 
but is unknown, except as worn pebbles in conglomerate, in any of 
the later formations. It is therefore of middle Miocene age. 
FERNANDO FORMATION. 
GENERAL CHARACTER. 
The line of demarkation between the Miocene and Pliocene forma¬ 
tions in the region about Los Angeles is not at all distinct. There is 
no doubt of the existence of a decided break between the white shale 
