In considering the two primary theories as to the origin of petroleum, whether inorganic--that is from chemical action on rocks forming part of the earth’s crust, or whether organic, from the decay of vegetable and animal matter--there are many strong arguments for both theories and it is quite reasonable to believe that both may be correct. There are localities where petroleum exists in formations showing little evidence of animal or vegetable remains and little possibility of having reached these formations by migration. As a rule, the production in such formations is small, rarely in commercial quantities, and it is probably derived from inorganic sources. This possibility is further demonstrated by laboratory experiments. On the other hand, it is probable that the greatest sources of petroleum are due to organic origin, more particularly in the carboniferous or the tertiary formations, where coal, cannel-coal, lignite, and other similar products are most frequently found. Hydro-carbons identical with most of the products of the distillation of petroleum, are so commonly obtained from the distillation of coal, lignite, and even bituminous shale and peat that in most cases the organic theory of the source of petroleum appears to be the correct one. Natural gas usually exists in association with oil deposits and in a great measure has the same properties, its existence as a gas or a liquid being dependent on the temperature and pressure under which it is held. In recent years, before it is sold for consumption as natural gas, it has become the general practice of oil producers to compress and chill the gas to obtain a considerable yield of gasoline which exists in the natural gas as a vapor. Another process for extracting this gasoline is by absorption, that is, passing the gas under a comparatively low pressure through a heavy oil, which takes out a part of the gasoline from the gas. In both processes, but especially in the high compression system, there is a considerable percentage of very volatile gasoline obtained, which is highly explosive and difficult to retain as a liquid. Varying in different localities and under different conditions, natural gas yields commercially from one-half gallon to five gallons of gasoline per thousand cubic feet, although extreme cases show much wider range.