I think this discovery also supports the theory that the origin of petroleum in nature is produced by moderate heat on coal or similar matter of a vegetable origin. For we know from the researches of Freund and Pebal (_Ann. Chem. Pharm._, cxv. 19), that petroleum contains phenol and its homologues, and as I have found this organic compound in the coniferae of to-day, it is probable that petroleum in certain areas has been produced from the conifers and the flora generally of some primaeval forests. It is stated by numerous chemists that "petroleum almost always contains solid paraffin" and similar hydrocarbons. Professors Schorlemmer and Thorpe have found heptane in Pinus, which heptane yielded primary heptyl-alcohol, and methyl-pentyl-carbinol, exactly as the heptane obtained from petroleum does (_Annalen de Chemie_, ccxvii., 139, and clxxxviii., 249; and _Berichte der Deutschen Chemischen Gesellschaft_, viii., 1649); and, further, petroleum contains a large number of hydrocarbons which are found in coal. Again, Mendelejeff, Beilstein, and others (_Bulletin de la Societe Chemique de Paris_, No. 1, July 5, 1883), have found hydrocarbons of the-- C_{n}H_{2n2+}, C_{n}H_{2n-6}, also hydrocarbons of the C_{n}H_{2n} series in the petroleum of Baku, American petroleum containing similar hydrocarbons. I think all these facts give very great weight to the theory that petroleum is of organic origin. On the other hand, Berthelot, from his synthetic production of hydrocarbons, believes that the interior of the globe contains alkaline metals in the _free_ state, which yield acetylides in the presence of carbonic anhydride, which are decomposed into acetylene by aqueous vapor. But it has been already proved that acetylene may be polymerized, so as to produce aromatic carbides, or the derivatives of marsh gas, by the absorption of hydrogen. Berthelot's view, therefore, is too imaginative; for the presence of _free_ alkaline metals in the earth's interior is an unproved and very improbable hypothesis. Byasson states that petroleum is formed by the action of water, carbonic anhydride, and sulphureted hydrogen upon incandescent iron. Mendelejeff thinks it is formed by the action of aqueous vapor upon carbides of iron; and in his article, "Petroleum, the Light of the Poor" (in this month's--February--number of _Good Words_), Sir Lyon Playfair, K.C.B., F.R.S., etc., holds opinions similar to those of Mendelejeff.