No question in geology is more obscure than that of the origin of the numerous natural hydrocarbons commonly classified as asphalt, ozokerite, petroleum, and natural gas. Certain facts of occurrence and certain results of experiment are indeed established, but the interpretation to be placed upon them is so doubtful that the conclusion reached may almost be said to depend on predilection. A great number of the more important hydrocarbons found in petroleums can be produced artificially from organic substances, such as coal, wood, and fish oil, while identical or closely allied hydrocarbons result from the interaction of inorganic substances, such as cast iron and chlorhydric acid. In many places petroleum is closely associated with fossiliferous strata; but hydrocarbons likewise exist in meteorites and in volcanic gases; they are even expelled by heat from granite and basalt. The most orthodox opinion at the present day is that a part of the natural hydrocarbons is of organic origin and a part also of inorganic origin; but when it comes to estimating the relative importance of the two portions there is no approach to unanimity. Before making a suggestion, which in this connection appears to be of interest, it may be well to outline the arguments for the opposing views.
