The area here described, and shown on the map (figure 1) covers the Fairfield, Gettysburg, and Carlisle quadrangles and the immediately adjacent region. These three quadrangles were surveyed by the writer for publication in folios of the geologic atlas of the United States. The mapping of the adjacent region is taken from published State geologic maps of Maryland and Pennsylvania somewhat modified.
The Triassic igneous rocks of this area, with the possible exception of a thin sheet just south of Bendersville, are all intrusive diabase and include one large sheet, several cross-cutting bodies, and many small sheets and dikes. Their distribution is shown on the accompanying map, figure 1. The concealed and weathered condition of the exposures make it difficult to determine the mode of occurrence of some of the masses, but the relations shown in the sections (figure 2) . . .