110 
SANTA MARTA OIL DISTRICT, CALIFORNIA. 
but the Eocene shales in which it is characteristic, or in which 
it occurs in appreciable quantity except locally, although there are 
numerous formations which would be capable of storing oil if any 
had originated in them. Moreover, the bituminous Monterey shale 
of the Coast Ranges does not occur consistently above or below 
any one formation from which the oil could have been derived. It 
lies unconformably upon ancient metamorphic rocks; granite and 
other igneous rocks; Jurassic, Cretaceous, or early Tertiary sedi¬ 
ments; or conformably over lower Miocene beds, according to local 
conditions; and it is either not covered by later deposits or is buried 
by sediments of various ages, in different places. 
The decision is therefore unavoidable that some ingredients of the 
Monterey shale gave rise to the oil, and the question arises what these 
were. The organic composition of the strata making up this forma¬ 
tion is discussed on pages 38-43, where a number of animal and 
plant forms that may have contributed to the oil are enumerated. 
The writers are strongly of the belief that the petroleum was derived 
largely from the minute organisms, especially the plant organisms 
(diatoms), which are present in such abundance in these shales. The 
chemists Peckham and Clarke believe that the nitrogen present in 
the California oil proves its origin from animal substance. But it is 
not necessary to consider that this petroleum originated entirely 
from either animal or vegetable matter; it is more probably the 
product of remains of both kinds combined, much of the nitrogenous 
material being furnished by animal tissue. 
Other small organisms of a low order present in the Monterey shale 
besides the diatoms are Foraminifera and Radiolaria, both orders of 
marine animals. They became embedded in the mass of the organic 
and adventitious silt material of the deposit at the sea bottom, and 
their bodies were thus preserved with the hard parts and may have 
become a source of hydrocarbons and nitrogen for the petroleum. 
The fact that the limestone and calcareous shale of the Monterey are 
usually very bituminous suggests the conclusion that the Foraminif¬ 
era were great oil formers, inasmuch as these rocks are thought to be 
made up largely of foraminiferal remains, although of course the 
calcareous strata may owe their petroliferous character to their 
porosity. In many places the body o£ the limestone is full of minute 
specks of oil contained in cavities about the size of the interior of 
foraminiferal skeletons, and these specks give the impression that the 
oil is not far from its point of origin. Albert Mann, of the United 
States Department of Agriculture, makes the suggestion that possibly 
Foraminifera originally made up a greater part of the shales than 
now appears and that tlieir easily destroyed calcareous tests were 
leached out, the soft parts adding their quota to the total amount of 
petroleum formed and owing to their animal character helping to 
