Ordovician shale forms a broad belt, about 10 miles wide, across the southeastern part of Pennsylvania, from Greencastle on the southwest to Belvidere, New Jersey, on the northeast. It lies northwest of the Great Valley, a limestone valley locally called Cumberland Valley, southwest of Susquehanna River, and Lebanon, Reading, and Allentown valleys, successively to the northeast. The name Martinsburg has been applied to the shale throughout this belt. A rather large area, 17 miles long, which is connected with the main belt at Hummelstown, extends southwest to Shepherdstown and is referred to as the Steelton area. Many small areas of Ordovician shale occur southeast of the main belt, most of which lie north of the Triassic basin. They are shown on the map, figure 1, and will be described under the following names: Schaefferstown, Shillington, Wyomissing, Oley Valley, Limeport, Jutland, Doylestown, and Cocalico shale areas. The shale in . . .