DISTRIBUTION AND MODE OF OCCURRENCE 627 



it is still united with the cross-cutting mass. Two sills leave the cross- 

 cutting mass north of Fairfield. One extends northeastward between the 

 bedding planes and appears to divide into 3 sheets, inclosing sedimentary 

 layers in part of its course. The other lies west of the cross-cutting body 

 and follows the flat contact of the overlapping Triassic sediments on the 

 Paleozoic limestone. This sheet is apparently of wide extent and, al- 

 though it rises somewhat into the sedimentary beds of the Triassic in 

 places, it is generally at or close to the overlap contact and will be here- 

 after referred to as the "overlap-contact sill." This relation is well shown 

 in the isolated igneous mass resting on the limestone north of Fairfield. 

 At the western edge of the basin this sill is cut off by the bounding nor- 

 mal fault and is concealed beyond to the north. The loop of diabase 

 northeast of Cashtown is a folded sheet apparently at a slightly higher 

 horizon, but the band exposed along the western edge of the Triassic far- 

 ther northeast is probably the outcrop of the overlap-contact sill. The 

 narrow loops of diabase at Bendersville are thin folded sheets apparently 

 higher above the base, and one of them seems to be a surface flow. The 

 overlap-contact sill is identified again in the valley northwest of York 

 Springs, where it rests on the Paleozoic limestone floor. 



A short cross-cutting body leaves the upper side of the Gettysburg sill 

 5 miles northeast of Gettysburg, and a longer one branches off 5 miles 

 farther on. The latter sends off several small sheets between the sedi- 

 mentary layers on both sides, and at its western end, where it swells to 

 greater dimensions, a larger intrusive body leaves it and runs northward. 

 This body is believed to be a sheet which is extensively exposed also in 

 adjacent valleys to the west and east and is there overlain by thick beds 

 of conglomerate. Since the conglomerate is known to overlap the Paleo- 

 zoic limestone floor nearly horizontally from the western border of the 

 Triassic to York Springs in a near-by valley, it is believed that the lime- 

 stone floor lies only a short distance below the intrusive sheet just de- 

 scribed, which is even nearer the western border, and that this sheet is 

 the same as the overlap-contact sill which was traced northward from 

 Fairfield. This is borne out by the fact that one of the areas of its out- 

 crop connects at the north with the overlap-contact sill that lies on the 

 Paleozoic limestone floor northwest of York Springs. 



The diabase sill northwest of York Springs follows the limestone out- 

 crop northward to where it disappears along the bounding fault. From 

 there it passes northeastward toward Dillsburg, dividing into two bands, 

 one terminating in the cross-cutting mass that extends east from Dills- 

 burg, the other continuing past Dillsburg to another large cross-cutting 

 body. These two cross-cutting bodies unite into one large mass which 



