HAYES AN 
KENNEDY 
D ] OEIGIN OF PETROLEUM. 139 
diatoms in the mud at Sabine Pass is regarded by Dr. Phillips as fur- 
nishing some degree of support to this theory. 
The majority of geologists have held to the second theory, namely, 
that petroleum is derived from the organic matter disseminated 
through great masses of carbonaceous shales by the process of slow 
natural distillation at relatively low temperatures, and that it has 
subsequently migrated through the strata to the reservoirs in which 
it is found. In proof it is pointed out that these carbonaceous shales 
yield by artificial distillation a large quantity of hydrocarbons, both 
gaseous and liquid, which are indistinguishable from those found in 
nature; but the possibility of natural distillation at a temperature 
sufficiently low to leave the inclosing rocks entirely unchanged has 
not been proved, nor have the residues of carbon which would result 
from such distillation been found in the rocks. 
Again, there is much diversity of opinion among those who hold to 
the organic origin of petroleum as to whether its source is in animal 
or vegetable remains. Peckham believes that petroleum may be 
derived from both animal and vegetable matter, but that the source 
of the organic matter determines the- character of the oil, that with a 
paraffin base (e. g., Pennsylvania) being derived from plant remains, 
and that with an asphalt base (e. g., California) being derived from 
animal remains. 
THEORIES OF COMBINED ORGANIC AND INORGANIC ORIGIN. 
Among the theories whicli fall in the third group may be mentioned 
that proposed by O. C. D. Ross ffl in 1891. It is that petroleum is 
produced by the action of volcanic or solfataric gases containing 
sulphurous acid and hydrogen sulphide upon limestone, with the for- 
mation of gypsum and free sulphur. The reactions given undoubt- 
edly take place in the laboratory, and they may also take place in 
certain localities in nature. On the other hand, Hopkins b proposed 
a theory, which has been elaborated and modified somewhat by other 
chemists, according to which the gypsum is the original material and 
the limestone is secondary. The essential features of this theory are 
that gypsum, calcium sulphate, in the presence of decomposing 
organic matter which gives off carbonic acid, is reduced, with the for- 
mation of limestone, calcium carbonate, free sulphur, and hj^dro- 
carbons. This reaction has not been exactly reproduced in the 
laboratory, but neither can the conditions which must prevail at 
great depths in the earth be exactly reproduced. 
It will be observed that the theories of this group are intermediate 
between those of the first two classes. The original materials are in 
part organic (limestone and vegetable or animal matter) and in part 
inorganic (volcanic gases and gypsum). 
« Chemical News, Vol. LXIV, 1891. 
^Repoi-t on the Geology of Louisiana, 1869. 
