The chief characteristics of petroleum strata are enumerated as:

I. The existence of adjoining beds of limestone, gypsum, etc.

II. The evidence of volcanic action in close proximity to
them.

III. The presence of salt water in the wells.

I. All writers have noticed the presence of limestone close to
petroleum fields in the United States and Canada, in the Caucasus, in
Burma, etc., but they have been most impressed by its being
"fossiliferous," or shell limestone, and have drawn the erroneous
inference that the animal matter once contained in those shells
originated petroleum; but no fish oil ever contained paraffin. On the
other hand, the fossil shells are carbonate of lime, and, as such,
capable of producing petroleum under conditions such as many limestone
beds have been subjected to in all ages of the earth's history. All
limestone rocks were formed under water, and are mainly composed of
calcareous shells, corals, encrinites, and foraminfera--the latter
similar to the foraminfera of "Atlantic ooze" and of English chalk
beds. Everywhere, under the microscope, the original connection of
limestone with organic matter--its organic parentage, so to speak, and
cousinship with the animal and vegetable kingdoms--is conspicuous.
When pure it contains 12 per cent. of carbon.

Now petroleum consists largely of carbon, its average composition
being 85 per cent. of carbon and 15 per cent. of hydrogen, and in the
limestone rocks of the United Kingdom alone there is a far larger
accumulation of carbon than in all the coal measures the world