The Piedmont of Maryland occupies a belt about 55 miles wide, extending across the central part of the State from the Pennsylvania-Maryland line to the Potomac River. Its southeastern edge is the “Fall line,” marked by such towns and cities as Elkton, Havre de Grace, Baltimore, Laurel, and Washington, and its northwestern boundary is Catoctin Mountain. The Piedmont is for the most part a rolling upland underlain by pre-Cambrian crystalline rocks, and it comprises, in the western part, the Frederick Valley, underlain by Paleozoic rocks, and the Triassic lowland which lies along the eastern edge of Catoctin Mountain.
The area of the pre-Cambrian rocks of the Piedmont of Maryland is divided for geologic reasons into an eastern and a western belt by the Peach Bottom syncline, which crosses the Pennsylvania-Maryland line at its intersection with the Susquehanna River, north of Conowingo. This syncline extends southwest from Cardiff through Greystone, . . .