Paleozoic, a schist, a metamorphic rock containing garnet, staurolite, kyanite, and sillimanite. Varieties include oligoclase-mica schist. As the Poquessing passes along the border between Philadelphia and Bucks County, the Pennsauken and Bridgeton Formations, from the Tertiary, consisting of quartz sand, overlie the Wissahickon Formation, but the creek has eroded below these formations to flow along the Wissahickon Formation. Then, the last few hundred yards (meters) before emptying into the Delaware River, it flows through the Trenton Gravel formation, from the Quaternary, consisting of reddish-brown gravely sand and silt. Tributaries Black Lake Run Bloody Run Byberry Creek Colberts Run Elwoods Run Waltons Run Wilsons Run Historic bridges Several historic bridges cross the Poquessing. A two-span, closed-spandrel, stone arch bridge, built in 1805, originally carried the King's Highway, later the Byberry and Bensalem Turnpike. It was improved in 1917 to carry the new Lincoln Highway but was bypassed by the Roosevelt Boulevard in 1921. It is open to pedestrian traffic only. A three-span stone arch bridge, built in 1845, carrying Red Lion Road near the site of the old Red Lion Inn is still in use. A two-span, closed-spandrel, stone arch bridge at Richlieu Road, built in 1840, is no longer in use. A two-span, , closed-spandrel, stone arch bridge at Century Lane, built in 1853 to connect the villages of Mechanicsville (now part of Philadelphia) and Elizabethtown, remains in use. A single-span concrete arch bridge where Frankford Avenue meets Bristol Pike (both U.S. Route 13), built in 1904, is notable for its early modern use of concrete. It was listed on the National Register of Historic Places in 1988 and remains in use today. A 19th-century four-arch stone bridge carries Amtrak's Northeast Corridor rail line (originally Pennsylvania Railroad) over the Poquessing and Grant Avenue in Philadelphia. The span over Grant Avenue has been improved to a concrete deck arch. Quotation From The History of Philadelphia's Watersheds and Sewers compiled by Adam Levine, Historical Consultant, Philadelphia Water Department: Poquessing Creek rises in Montgomery County, crosses the north-west line of the late township of Byberry, where it receives a branch which flowed mainly through Moreland. It there bends northward into the county of Bucks, again southward, when it touches the township line, and flows south-east and south-west, forming the boundary line of Byberry, and turning to the south-east enters the Delaware.—Bloody run empties into it at Carter's mill, Black Lake creek at Mechanicsville,