138 OIL FIELDS OF TEXAS-LOUISIANA COASTAL PLAIN, [bull. 212. 
those which ascribe it to an organic origin, and (3) those which 
involve both inorganic and organic agencies. 
THEORIES OF INORGANIC ORIGIN. 
In 1866 Berthelot suggested that water containing carbonic acid or 
an earthy carbonate coming in contact with metallic sodium or 
potassium at a high temperature might produce both liquid and 
gaseous hydrocarbons such as are found in various oil fields. In 1877 
Mendeljeff published his theory, which remains the most plausible of 
all the inorganic theories thus far proposed. Stated briefly, it is that 
water percolating downward through fissures in the earth's crust 
comes in contact, under conditions of high temperature and great 
pressure, with metallic carbides ; that a chemical reaction takes place, 
with the formation of metallic oxides and saturated hydrocarbons, 
and that the latter ascend and impregnate the porous beds of sedi- 
mentary rocks in which they are now found. 
Various modifications of the theories of Berthelot and Mendeljeff 
have been suggested by other chemists, but these contain the essen- 
tials of all the purely inorganic theories which merit consideration. 
The fact is unquestioned that hydrocarbons similar to or identical 
with some of the constituents of natural petroleum may be produced 
in the laboratory b} 7 the action of inorganic substances, but no geo- 
logic or other evidence that these reactions actually take place in the 
earth's crust has been discovered. The conclusion must therefore 
be that while the inorganic theory is attractive it is not proved. 
THEORIES OF ORGANIC ORIGIN. 
These theories may be again divided into two groups : (a) That petro- 
leum is indigenous to the rocks in which it is found, and (b) that it is 
the product of natural distillation. 
The first of these theories was advocated by Sterry Hunt, who 
asserted that all petroleum was formed in limestone by the decompo- 
sition of the animal remains which it originally contained. It was 
also advocated by Lesley and Whitney. 
The theory was further amplified by Orton, who extended it to the 
petroleum found in the shale and sandstone in the Appalachian field 
as well as that found in limestone. According to Orton, a petroleum 
results from the primary decomposition of organic matter, and was 
formed when the rocks containing it were themselves formed. 
A modification of this theory has recently been advanced, namely, 
that the oil, instead of being the product of decomposition of 
organic matter, is secreted by living organisms of a low order, such 
as diatoms, and therefore exists as such as an original constituent of 
the rock in which it is found. The presence of oil associated with 
« Ann. Rept. Geol. Survey Ohio, 1890, p. 85. 
