Natural Gas, combustible gas which escapes from beneath the soil in such quantities that it may be used for fuel or illuminating purposes. In its natural state the gas occurs in porous sedimentary rocks, and, when proper openings are made, it rises to the surface. Wells are drilled for gas, as for oil or water. Natural gas is the product of decay or distillation of organic matter buried in sand, mud etc. By its burial the organic matter is shut off from contact with the air, and hence the gases arising from its deposition and distillation are not completely oxidized. Organic matter is now being imbedded in sands and muds which are in process of deposition on lake and sea bottoms. Under proper conditions this might ultimately give rise to gas. Natural gas is really a mixture of several gases in variable proportions; among them marsh-gas (CH₄) and hydrogen are usually most abundant. Natural gas is widely distributed. It is extensively utilized in Indiana, Pennsylvania, Ohio, West Virginia, New York and California; to a limited but still important extent in Kansas and Kentucky; and to a slight extent in Utah, Colorado, Illinois, Missouri and Texas. The flow of gas from a well usually is of short duration. It may last for a few months or even years, but not indefinitely. The popular notion that the withdrawal of gas from beneath the surface leads to earthquakes is wholly without foundation. The gas occurs in the pores of rock, and its escape does not make the rock less firm or substantial. Gas occurs in rock formations of various ages. Some of it comes from rocks as old as the ordovician (see Geology), and some of it from formations as young as the tertiary or even pleistocene. Natural gas and petroleum are probably associated in origin, as they often are in their distribution.