Linear features (lineaments) have been discerned in Erie County from multi-temporal Landsat MSS images and return-beam vidicon scenes. This 2,107 km² (814 mi²) portion of the Appalachian Plateau is criss-crossed by at least 24 Landsat linear features, some of which may be of

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structural origin. The lengths range from 7.25 to 24 km (4.5 to 15 mi) within the county. However, some lineaments extend for many kilometers outside of the mapped area.

There are two major sets of Landsat lineaments in Erie County. They are oriented approximately northwest-southeast and northeast-southwest. The vectors of the dominant set average 329° and those of the secondary set average 49°. The 329° set approximately coincides with the average regional dip of mapped subsurface beds. The 49° set generally corresponds to regional subsurface strike.

A detailed structural interpretation on the top of the Queenston Formation shows that some of the northwest lineaments locally coincide with dip reversals and other anomalies. This mapped horizon is the base of the Lower Silurian Medina Group which is currently the principal gas-producing reservoir in this region.

Lineaments which have a tectonic origin are surface expressions of faults and other structural disturbances which probably affected the crystalline basement and were repeatedly reactivated during the deposition of overlying beds.

Extensional fractures (fracture traces) interpreted from enlarged aerial photographs are abundant. The fracture traces are found in the surface lineament zones as well as in areas between lineaments. These fractures, at depth, can locally enhance the porosity and permeability of reservoir beds which, normally, are classified as "tight formations."

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