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 contains. A range of limestone rock 100 miles in length by 10 miles in width, and 1,000 yards in depth, would contain 743,000 million tons of carbon, or sufficient to provide carbon for 875,000 million tons of petroleum. Deposits of oil-bearing shale have also limestone close at hand; e.g., coral rag underlies Kimmeridge clay, as it also underlies the famous black shale in Kentucky, which is extraordinarily rich in oil. II. As evidence of volcanic action in close proximity to petroleum strata, the mud volcanoes at Baku and in Burma are described, and a sulphur mine in Spain is mentioned (with which the writer is well acquainted), situated near an extinct volcano, where a perpetual gas flame in a neighboring chapel and other symptoms indicate that petroleum is not far off. While engaged in studying the geological conditions of this mine, the author observed that Dr. Christoff Bischoff records in his writings that he had produced sulphur in his own laboratory by passing hot volcanic gases through chalk, which, when expressed in a chemical formula, leads at once to the postulate that, in addition to sulphur, _ethylene_, and all its homologues (C_{n}H_{2n}), which are the oils predominating at Baku, would be produced by treating: 2, 3, 4, 5 equivs. of carbonate of lime (limestone) with 2, 3, 4, 5 " sulphurous acid (SO_{2}) and 4, 6, 8, 10 " sulphureted hydrogen (H_{2}S); and that marsh gas and its homologues, which are the oils predominating in Pennsylvania, would be produced by treating: