• Occurrence, Geological Horizons, etc.— In the United States the principal sources of natural gas are located on the west slope of the great Appalachian uplift, extending from New York through Pennsylvania and West Virginia to southern central Kentucky with a considerable portion of southeastern Ohio, also along the northern portion of the great Cin cinnati uplift in northwestern Ohio and cen tral Indiana and southeastern Kansas. There has been recently developed an important nat ural gas field in eastern central Ohio.
In California, Texas, Louisiana, Colorado, South Dakota and Alaska gas is found in geo logically more recent rocks, but no attempt is here made to correlate the rocks of one field with those of another. In the Mississippi Val ley to the eastward natural gas occurs almost universally in rocks. of Palaeozoic Age, extend ing from the highest Carboniferous down at least as far as the Trenton limestone, a distance of over 9,000 feet. The rocks vary greatly in thickness from place to place, so that no one section can be regarded as typical of all parts of the region. The 50 gas-bearing horizons known are composed of very different material, ranging from the coarser sandstones of the Upper Carboniferous and Catskill period to the finer sands of the Middle and Lower Devonian, the limy sands of the Silurian period, the crys talline limestones of the Ordovician and the crystalline sands of the Cambrian period.
So far as at present discovered there are five great gas fields in the United States, the Pennsylvania and West Virginia field; the Kansas field; the Oklahoma field; the Louisi ana field and the California field. During 1915 two wells in Montana flowing 6,000,000 cubic feet per day were opened, and there have been promising developments in new grounds in •Indiana, Kentucky, Oklahoma and Louisiana. There were, in 1915, 23 States in which • some natural gas was produced, though the yield was notably large only in nine. In all, the gas-yielding territory of the United States covers about 9,365 square miles, of which some 10,600,000 acres are being ac tively exploited by gas producers. The States that produce large quantities of natural gas, as Pennsylvania and West Virginia, distribute it to the adjoining States by a system of pipe lines, so that in some instances the natural gas consumed in a town or city is produced over 200 miles from where it is consumed. Thus
Oklahoma and Kansas pipe gas into Missouri; Louisiana into Arkansas and Texas; Illinois into Indiana and Oklahoma into Arkansas.
In many localities the yield of gas is inci dental to the production of petroleum, and the former has been frequently sacrificed for the more stable fuel. This is the case particularly in the Caddo field of Louisiana, where billions of feet of gas have been allowed to escape un hindered. For some years open gas vents known as aroarers)) were of interest only as a night spectacle when, having been ignited, their flames, a hundred feet in height, lighted up the surrounding country. It is a satisfaction to record that in most localities this waste has been checked. Another avenue of serious waste, when the totals are considered, is that which has occurred in boring for oil. This, too, has been overcome by sealing the gas sands with clayey mud, when they are encoun tered in the search for oil.
Production of Natural Gas in the United No other country enjoys the luxury of natural gas to the extent of the people of the United States. It is used in Canada and in a very limited way in England, Australia, Germany, Rumania, Galicia, Russia, Persia, In dia, China and Japan, but all these countries combined use only 2 per cent of the known world's commercial production of this efficient and convenient fuel, leaving 98 per cent to be consumed by the people of the United States. The total value of the natural gas produced and sold since its introduction, commercially, in the United States, in 1872, up to the close of 1915 was $1,164,717,474. Assuming the average price of the last 25 years, 12 cents per 1,000 cubic feet, this value should represent 9,705,978,950, 000 cubic feet in amount. If it were possible to confine this immense quantity in a tank whose end was one square mile in area it would require to be 630 miles in length. Its heating value would equal 945,000,000 tons of coal. Large as this quantity seems, it is quite probable that it does not represent one-half of the actual quantity which has flowed from the earth's rocky reservoirs since the discovery of petroleum. The loss in developing petroleum fields has been so great that these figures, rep resenting only that amount of gas which has been collected and sold on a commercial basis, give little idea of the actual evolution from the great gas reservoirs.