662 The American Naturalist. [July, 
ous to and derived from certain limestones, as Hunt has so strongly 
asserted. On the other hand, Newberry’s doctrine that the great sup- 
plies of the Pennsylvania field are derived from Devonian shales is be- 
coming more firmly established and widely accepted every year, 
though it seems likely that he has laid too much stress on bituminous 
shales. In other words, the theories are not incompatible with each other. 
Different fields have different sources. We can accept without incon- 
sistency the adventitious origin of the oil in Pennsylvania sandstones, 
and its indigenous origin in the shales of California or in the lime- 
stones of Canada, Kentucky, or Ohio. 
The double origin of petroleum from both limestones and shales— 
and it is not necessary to exclude sandstones from the list of possible 
sources—deserves to be universally accepted. In confirmation of this 
double origin, it is coming to be recognized that the gas and oil de- 
rived from them two sources—limestones and shales—generally differ 
from each other in noticeable respects. The oil and gas derived from 
limestones contain larger proportions of sulphur and nitrogen than 
are found in the oil and gas of the shales. Nitrogen renders the oils 
unstable, and sulphur compounds impart to them a rank and persistent 
odor from which they can be freed only with great difficulty. In the 
case of the oil-bearing shales of California, the petroleum is evidently 
derived from the animal remains with which the formation was orig- 
inally filled. In composition this oil agrees with the limestone oils 
already described. It contains more than four times as much nitrogen 
as the Mecca oil of northeastern Ohio, and its percentage of sulphur 
is very high. Peckham says of the Pennsylvania oils :? 
** The exceedingly unstable character of these petroleums, consid- 
ered in connection with the amount of nitrogen that they contain and 
the vast accummulations of animal remains in the strata from which 
they issue, together with the fact that the fresh oils soon become filled 
with the larvae of insects to such an extent that pools of petroleum be- 
come pools of maggots, all lend support to the theory that the oils are 
of animal origin.” 
He speaks again of this class of petroleums as formed of animal 
matter that has not been subjected to destructive distillation.? 
It now appears as if oil and gas derived from animal remains can be 
distinguished from those of the bituminous shales by the characters 
above described. Certain it is that the *«limestone oils’’ differ in 
physical characteristics from the Pennsylvania oils, for example, in a 
? Op. Cit., p. 69. 
3 Ibid., p. 71. 
