Forty selected core samples of ''Devonian shales''from two wells in western and southwestern West Virginia were analyzed petrographically. Lithologically these samples may be grouped into 6 rock types: shale, silty shale, dolomitic shale, shaly siltstone, shaly dolostone, and dolostone. Mineralogically, illite comprises the major part of the argillaceous fraction, whereas quartz constitutes the principal nonclay mineral. Carbonate is present in most specimens and is generally dolomitic. The most prevalent heavy mineral is pyrite. Dark gray (N3) to brownish-black (5YR2/1) organic, rich shale constitutes the most distinctive rock type in the principal ''Brown shale pay zone interval. Organic matter occurs in several forms and comprises as much as 4.4% of the shale. Vertical mineral-lined fractures are important in facilitating gas accumulation and migration in most pay zones. Dolomite is the main mineral constituent in these linings; however, small amounts of calcite and barite are also present. Mineral linings serve as propping agents to hold fractures open and thus are important in maintaining porosity and permeability along the fractures. Lenses of silt-size quartz and feldspar may serve as conduits for movement of gas into these fractures. (16 figures)
