This field trip provides an overview of both the geology underlying the city of Philadelphia and the hydrology of the Schuylkill River watershed. Philadelphia is located at the contact between two major East Coast physiographic provinces, the New Jersey Coastal Plain and the Piedmont. The Piedmont rocks are examined during this field trip. In this area, the Piedmont exhibits low to moderate relief and is underlain by folded and faulted sedimentary and metasedimentary rocks of early Paleozoic age. These rocks are interpreted to represent the collision of a magmatic arc with a continental landmass and adjacent forearc basin sediments during the early Paleozoic; they are intensely deformed and metamorphosed to the amphibolite and granulite facies. The Piedmont rocks appear in the type section of the Wissahickon Formation, which will be the geologic focus of this field trip. The hydrology of the Schuylkill River and one of its major tributaries, Wissahickon Creek, will also be discussed during the trip.