The Honeybrook uplift lies on the east side of the large Paleozoic limestone lowland around Lancaster in the Piedmont of southeastern Pennsylvania. This lowland is an embayment of the limestones of the Appalachian Valley into the Piedmont area around the plunging end of folds of Cambrian quartzites of South Mountain, which is the northern extension of the Blue Ridge (Fig. 1). The Honeybrook uplift brings Cambrian quartzites and pre-Cambrian basement rocks to the surface on the east side of the limestone lowland. Chester Valley, a long narrow synclinal limestone valley of east-northeast trend, lies south of the Honeybrook uplift, which is overlapped on the northeast side by gently north-dipping Triassic redbeds.
This paper is the result of detailed studies for a report on the Honey-brook and Phoenixville quadrangles to be published by the United States Geological Survey. The pre-Cambrian rocks, which were mapped by Florence Bascom and will . . .