The Pennypack flows south out of the Pennypack Preserve, enters Montgomery County's Lorimer Park, then crosses the line into the city of Philadelphia where it flows within Pennypack Park all the way to its mouth at the Delaware River. About two miles upstream of its mouth, the creek falls off the hard edge of North America and flows onto sediments deposited on the shallow continental shelf - the Coastal Plain. The transition from the hard, ancient Piedmont rock so familiar to visitors to the Pennypack Preserve to the sandy Coastal Plain - the fall line - is dramatic.
|Pennypack Creek at the fall line|
The Piedmont bedrock at the fall line displays graphic evidence of the repeated stresses experienced by the rock at the edge of the continent. North America and Africa have collided with one another on at least two occasions, and the bedrock, composed mostly of dull, gray metamorphic gneiss, is twisted and bent like taffy. In addition, other types of rock have gotten caught-up in the collisions and been incorporated into the cooled "taffy" like the quartzite in the image above, and the granite in the image below.
|A stone studded with mica|
The pools created by this fish ladder have become very popular swimming holes with members of the Hispanic community in the neighborhood. Although swimming is prohibited, and the creek is far too "impaired" for safe contact, that doesn't stop the kids from cooling off. Fortunately, if the shad begin to use the creek for spawning again, they would return in March and not have to contend with crowds of kids.
|Requisite sycamore-against-blue sky image|
The fall line's a pretty "happening" place!
Submitted by David Robertson