Devonian Marcellus Formation Maps
In recent years it has received an explosion in attention from the energy development community because of it's potential as a source of untapped natural gas. This is particularly important because the Marcellus formation exists in an area of North America where the demand for energy is also high.
The result of this combination of factors is a drastic increase in the value of drilling rights for natural gas in the areas on top of the Marcellus shale, namely western and northern Pennsylvania, Southern New York, and most of West Virginia.
What does it look like? One can see Marcellus Shale is several areas of Central Pennsylvania where it has been "peeled" to the surface. Dr. Terry Engelder has documented these on his web-site, http://www.geosc.psu.edu/~engelder/marcellus/marcellus.html