The problem of the origin of petroleum has been the subject of considerable scientific controversy for many years. Not a few of the leading scientists hold to the theory that petroleum is derived from metallic carbides lying far beneath the porous strata in which the oil is stored by Nature, and that even at the present time the process is in operation. This idea, which may be termed the inorganic theory of petroleum origin, was considered to have received substantial support when it was found that the action of water on the carbides of certain metals resulted in the liberation of hydrocarbons. The view that petroleum is of organic origin is to-day almost universally accepted, although there is no general agreement either as to whether petroleum is derived from vegetable or animal matter, or as to the forms of life that provided for its genesis. In certain places in the world--notably on the eastern side of the Caspian Sea and also near the Mediterranean--there is some conversion of organic matter into petroleum actually to be seen to-day. It is not difficult, as the late Sir Boverton Redwood, Bart., pointed out in an address before the Royal Institution of Great Britain in 1918, to account for the formation of adequate deposits of the necessary material. In the comparatively deep and quiescent water along the margin of the land in past ages, there would be abundant opportunity for the deposition not only of the remains of marine animals and plants, but also of vegetable matter brought down to the coast by the water courses, and the changes which the earth has undergone would result in the burial of these substances under sedimentary mineral matter, the deposits thus formed being ultimately, as the result of further alterations in the earth’s surface, frequently found occupying positions far removed from the sea, and sometimes beneath immense thicknesses of subsequent deposits. That vegetable matter may be the source of certain petroleums is an opinion that has found increasing evidence to support it. There are two kinds of vegetable matter which are possible, terrestrial and aquatic, and in the deltaic conditions that characterize so many oil-fields, either could be equally well appealed to as a source of accumulation. The extensive coal and lignite deposits in many geological periods bear eloquent testimony to the presence of carbonaceous matter far in excess of that required to provide proved supplies of petroleum. Every important coal-field demonstrates the fact that vegetable matter can be partially converted into bituminous compounds or hydrocarbons by natural processes. Marsh gases often occur in great quantities in faulted zones in the coal measures, though the bituminous substances found in coal are not true bitumens that dissolve in the usual solvents, while the tars derived from the destructive distillation of coal in no way resemble natural petroleums or the products of oil-shale distillation.