Abstract Commercial production of natural gas in the Lima-Indiana district of Indiana and Ohio began in 1884–1886. Ten years later the largest area known to produce gas from rocks of Ordovician age was proved and outlined. The district extends in a curve for a distance of about 150 miles and covers an area of about 12,000 square miles. Only a few gas fields of small areal extent were found in Ohio; those in Indiana were numerous and large. All are now mostly exhausted. Most were coextensive with oil fields. In Indiana the gas field areas lie across the crest of a broad structural arch, in Ohio mostly east of the axis of a northward pitching anticline, according to published subsurface structure maps. Descriptions of local structures have not been published. Subsurface anticlines with 125 feet of structural closure, beds dipping at the rate of 40–120 or more feet per mile, and north-south axes are known in Indiana. In Ohio a fault with 100–200 feet of displacement and a general north-south trend is known. In Indiana at least, it appears that the commonly published structural form and attitude of the Cincinnati arch are not correct. The gas- and oil-bearing horizons occur in a dolomitic limestone zone of Ordovician age, mostly in the upper 50 feet of the “Trenton” formation. Porosity and percentage content of magnesium carbonate are considered to have been the controlling factors in trapping the occurrences. The writer believes that folding and genetic sites have been at least equally important as factors in determining the occurrences. Paleogeologic action, with earth movements of the arch active before Pennsylvanian time and possibly as early as Lowville (Middle Ordovician) time, is probably an important determinant.

Abstract The Production of petroleum, which in had been practically confined to the muddy valleys and hillsides around Oil Creek, Pennsylvania, expanded to global range duringthe next 20 years. In 1871 all but 525,000 barrels of the world’s production of 5,730,000 barrels of oil came from the narrow belt of country that the Drake well had opened. New developments followed rapidly. Exploitation of the nearby “Lower Belt” doubled Pennsylvania production in 1873 and halved the price to$1.80 per barrel. The Bradford, Pennsylvania-New York, field, with reserves of more thanone half billion barrels of high grade oil, was discovered in 1871 and grew slowly at first, but became the dominant market factor in 1877. The 500 million barrels of sulfurous oilin the Lima, Ohio-Indiana field, discovered in1885, introduced new problems into the oil industry. From 1878 through 1890 the averageprice of crude oil in the United States remained below $1.00 per barrel in every yearbut one. Drilling activities from West Virginiato California had some successes and many difficulties, but their immediate effects were ofonly local importance. A natural gas industrycame into being in 1883, with profound effectson the nation’s economic structure as manymanufacturers moved to take advantage of the cheap fuel. The United States’ share of world production declined from 91 percent in 1871 to lessthan 60 percent of the gross 76,633,000 barrelsof oil in 1890. Output in the United Statesgrew 9-fold during the 20 years, but that of therest of the world increased by a multiple of 59.The increase in North America came from newly