Vou. III] ANDERSON—NEOCENE DEPOSITS OF KERN RIVER 115 
been observed in any case, it is likely to have been found along 
certain directions, and belongs primarily to the sands rather 
than to the clays, since it would owe its origin to the sorting 
action of currents during deposition. However, the idea of 
this condition comes solely from a study of the well-records, 
and the faulty data furnished by some of these should not be 
forgotten. If a well-record fails to record a particular bed of 
clay, it does not prove its absence, but possibly only a failure 
to detect it. 
The structure of the beds is almost that of a simple mono- 
cline, but when studied in detail the beds undulate somewhat, 
forming slight anticlines and synclines striking N. W. to S. E. 
The ultimate areal extent of the field has not been proved 
by actual developments, though the limits may be definitely 
known toward the northeast, if not also toward the southwest. 
Thus far water has proved to be more troublesome on the 
southwestern border of the field; and this is partly on account 
of the thinner clay beds in this direction, and the greater 
difficulty met with in shutting it out from the wells, or in 
confining it to certain limits by means of these clays. 
The gravity of the oil varies from 10.4° B. to 17.0°, though 
a large percentage of the production is between 14.5° and 16° 
B. Still lighter oil comes from strata below the oil measures 
of the Kern River group. 
Water-sands, which are the source of much trouble, are 
found both above and below the productive beds—some 
within the oil-measures, though in some cases water has been 
let into the oil-measures by accident or by faulty drilling. It 
is usually possible to shut out the upper water, and when the 
horizon of the lower water-sands is once learned, drilling may 
be stopped above it. There are usually sufficient clays suitably 
situated for the control of the underground water if the condi- 
tions are correctly known beforehand. 
The question as to the origin of petroleum is one much 
debated; but in California there is overwhelming evidence in 
favor of an organic origin, and the facts point to certain low 
organisms of both marine and fresh-water habitat. In the 
Tertiary formations of California, Diatomaceae are extremely 
abundant, and beds that are largely composed of their remains 
