The most comprehensive research regarding the Marcellus Shale and other Middle and Upper Devonian organic-rich shales in the Appalachian basin was published as part of the U.S. Department of Energy's Eastern Gas Shales Project (EGSP) in the late 1970s. Maps created from data collected during that project have been reproduced as color documents in PDF format and are available for download. Three cross sections across NW and SW Pennsylvania show the thickness and distribution of the Marcellus in the subsurface. The section lines are oriented N-S (E-E') and E-W (A-A' and C-C'). These maps have been digitized and are available as shapefiles for use with a geographic information system (GIS). The map data can be downloaded in both polygon and line format. The shapefiles that contain map data in line format consist of lines corresponding to either depth or thickness depending on the map source data. Polygons represent ranges of data (thicknesses or depths). It may be necessary to use both the line and polygon data to digitally reproduce the original maps. The Pennsylvania Geological Survey assumes no responsibility for the accuracy or completeness of the information in the maps.