114 CALIFORNIA ACADEMY OF SCIENCES  [Proc. 41H Ser. 
often confined to 250 feet or less. Mechanical difficulties often 
make it impracticable to draw upon all of the sands capable of 
yielding oil, and the perforations of the casings are sometimes 
extended to only half the thickness of oil strata actually 
encountered in drilling. 
Below the base of the Kern River group and, therefore, 
within the Temblor, oil-sands have been reported in the records 
of the deep wells, but none of them are known to be capable 
of yielding commercial quantities of oil. The oil is generally 
reported to be of lighter character than that from the oil- 
measures of the Kern River group. Thin streaks of oil-sand 
and stains of oil, and shales more or less colored by bituminous 
matter, if not with oil, outcrop in certain localities within the 
Temblor. Some of these are to be seen along Kern River east 
of the oil-field, and in the hills north of Poso Creek as, for 
example, near the old fuller’s-earth mine. Oil-sands are 
reported in some old wells a quarter of a mile north of this 
mine, at a depth of 1300 to 1400 feet, and gas is still issuing 
from one of these wells in small quantity. 
Gas, which is generally regarded as an indication of oil, 
has been encountered in nearly all of the wells, old and new, 
that have been drilled into the Temblor beds. Considerable 
quantities of gas were found in both the Grace Well No. 5, and 
in the deep well of the Petroleum Development Company. 
Stratigraphically, the oil is not found in a single bed extend- 
ing across the field, but in sandy beds more or less separated 
by clays and distributed through the oil-measures. The sandy 
beds and clays interleave, often forming an alternating series 
throughout the measures. As a rule, in the developed portion 
of the field the sands are thicker in the eastern part of the 
field and become thinner toward the west, and the clays are 
thicker on the western border and become thin and scattered 
toward the east. In like manner the sands are thicker toward 
the south, and clays increase in volume northward. 
There is considerable lack of uniformity in the well-records; 
but this is probably due more to faulty records than to irreg- 
ularities in the beds themselves. Both sands and clay-beds are 
believed by some to be lenticular in section, and this is some- 
times given as the cause of troubles met with in controlling the 
underground water. But if a lenticular condition has really 
