The Medina (Silurian) and the Trenton (Ordovician) formations of New York are well known members of the Lower Paleozoic system. Both have their typical outcrops in New York state and both are present as concealed formations with a generally southern dip throughout almost all the western part of the state. Folds and faulting are practically absent. Two divisions of the Medina are recognized, the upper, known as the Albion sandstone, being the source of most of the Medina gas. The most prolific Medina fields are in the counties bordering Lake Erie. The fields are slow yielding of their gas and have a long life.

The Trenton formation is predominantly a limestone but contains numerous beds of shale. Gas may be found at many horizons in a single well and large pockets of gas are commonly encountered. Small but persistent flows have been maintained in several shallow pools near the east end of Lake Ontario for more than 35 years. Deep tests of the Trenton in other parts of the state have failed to yield outstanding results.