Natural gas is produced in the states of New York and Pennsylvania from rocks of Pennsylvanian, Mississippian, Devonian, Silurian, Ordovician, and Ozarkian age. The limits of production are defined in Pennsylvania by the highly folded and faulted area in the central part of the state and in New York by the Adirondack Mountains and the valley of the Hudson. From a historic standpoint this region is very interesting since the first natural gas well was drilled and the first natural gas transmission line was laid in this area. The stratigraphy of the area covers almost the entire Paleozoic system of rocks. These rocks were deposited in the northern end of the Appalachian geosyncline. The most important gas-producing horizons represent shore-line deposits or the fine sand deposits of deltas or partly enclosed bays. There are more than 50 gas-producing horizons and more than 200 separate gas fields in the area. The dominating structural features are the Appalachian geosyncline and the system of folds and faults which originated during the Taconic and Appalachian revolutions.
Gas occurrences in certain sandstones conform very closely to structural conditions but in general the character of the reservoir rocks is the most important factor in determining the accumulation of gas. The carbon ratio of the coals is an excellent index of the presence of oil or gas in the sandstones, but recent studies of certain of the more important reservoir rocks of the Chemung formation indicate that the permeability of the sandstone is of greater importance in limiting the area of oil production than the metamorphism of the rocks which was responsible for the progressive eastward devolatilization of the coals.
The supply of gas in this part of Pennsylvania at present exceeds market demands, whereas for several years New York's production has been supplemented by large amounts of imported gas. The proved reserves of the Pennsylvania fields combined with the large reserves of neighboring states should be ample to supply the demands of this territory for many years.