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The Schuylkill River in Geologic Time

In the history articles on this website we have looked back at the current neighborhood in what seem like grand time scales: decades back to Franklin Town; centuries back to the Baldwin Locomotive Works, Andrew Hamilton's Bush Hill, William Penn's Springettsbury Manor; and millennia back to the Lenni Lenape. Those time scales are miniscule compared to the intervals discussed in this article.

Sandy Owens, one of the original founders of our Friends group and the leader in getting the historical plaque honoring Matthias Baldwin in the northwest corner of the Park, looked at the geography of the Schuylkill and Delaware Rivers and considered some possibilities.

schuylkill basin.png
Schuylkill River watershed
Pa 1681 map.jpeg
A Map of the Improved Part of the Province of Pennsilvania in America: begun by Wil. Penn, Proprietary and Governour thereof anno 1681, by Thomas Holme
(from the Library of Congress)
The two-square mile City of Philadelphia, the land between two rivers, is in lower middle.
Note the generally north-south orientation of the rivers.
Philadelphia in 2019.
The blue dot represents Baldwin Park, close to the narrowest point between the Delaware and the Schuylkill Rivers.



Eventually, all things merge into one, and a river runs through it. The river
was cut by the world's great flood and runs over rocks from the basement of time.

                from the book A River Runs through It, by Norman Maclean

Look at a map of the Matthias Baldwin Park area that shows both the Schuylkill and
Delaware Rivers. Notice the narrow distance between the two rivers where the Schuylkill
bends in toward the Delaware. Long before the dam was built near the Philadelphia
Museum of Art, a canal was planned to run through the Callowhill Cut, linking the two
rivers. Nothing came of this plan and the Schuylkill continues its southward flow where it
runs into the Delaware River near League Island. Together the two rivers, now one,
empty into the Atlantic Ocean. The Schuylkill River is the largest tributary of the

I had a theory. Is it possible that 400 million years ago in the Paleozoic Era the Delaware
River was torn apart by a tectonic event? The tectonic plates slipped and warped; the
earth quaked; the Appalachian Mountains pushed up through the earth's crust; the
magma flowed and water wrenched from the Delaware became the Schuylkill, one river
torn apart into two. The last vestige of the waterway that linked the two rivers together
could be Pegg's Run, a creek submerged into a sewer pipe under Willow Street in the east
Callowhill industrial district. I turned to an expert, Eric Clausen, a geology teacher at OLLI in
Philadelphia, for a response. His answer was a firm no: did not happen. Wrong theory.

Clausen, who holds a PhD in geology from the University of Wyoming and capped his
long teaching career at Minot State University, North Dakota, with the title Professor
Emeritus, agreed that the flow and routes of rivers were altered by tectonic and seismic
events as well as glacial ice. The Rhine River in Switzerland is one example. At one time
it flowed into the English Channel rather than into the Atlantic Ocean near Rotterdam,
The Netherlands, as it does today. Locally, the Delaware River, Lehigh River, and
Susquehanna have all made sharp directional changes that are due to such events.

According to Dr. Clausen, "Wind Gaps provide evidence of places where rivers once flowed but were
diverted to flow in different directions. The classic example is Wind Gap, Pennsylvania,
21 miles north of Allentown. There are numerous other wind gaps throughout the
Appalachian Mountain region indicating that prior to today's river pattern, regional rivers
flowed along very different routes."

With tectonic activity, two plates collide with one plate going over or under the other.
Earthquakes may or may not be a part of tectonic movement, but tectonic activity can change the drainage routes of rivers. Water flowing downhill may change course and flow along a different gradient.
Glacial ice can block the flow of water sending a river on a different path. The quick
melting of huge ice sheets can cause massive floods sending water across upland areas.
This last situation is what Dr. Clausen proposes happened with the creation of the
Schuylkill River.

The origin of the Schuylkill River lies in the Appalachian Mountains. Geologists in the
late 19th century dated the Schuylkill back to the late Paleozoic Era. This assertion,
repeated over and over again without further research, has recently been challenged. The
current belief is that the Schuylkill is a much younger river than thought. It was created
by a massive glacial melt of the continental ice sheet before the last ice age. Melting
glacial flood waters flowed across New Jersey into the Philadelphia area.

What about earthquakes? The bedrock in many Philadelphia areas, notably Chestnut Hill
is Wissahickon Schist. It is a metamorphic rock formed at depths under great pressure in
the roots of an early Paleozoic mountain range. Old and inactive fault lines from millions
of years ago are evident in the Wissahickon Schist. Today a prominent fault line extends
across the Schuylkill Valley in the Conshohocken area to northern Chestnut Hill along
the valley traversed by Bells Mill Road; however, there is no evidence of a fault line in
the past eroding the Schuylkill River valley.

Dr. Clausen holds to the theory that erosion in the Schuylkill valley was caused by
flooding, not earthquakes. He says, "The low area that connects the Delaware and Schuylkill is a
water eroded landscape." Immense quantities of water flooded our area
where stand the Barnes Museum, Parkway Central Library, the Art Museum and
Matthias Baldwin Park. Clausen states, "The only known geological event capable of
producing such volumes of water would be the rapid melting of a large continental ice

A final imagining was asked of Dr. Clausen: If floods caused by the quick melting of the
continental ice sheet had not occurred between the Delaware and Schuylkill River, what
would this area look like today? Dr. Clausen: "All evidence of the previous landscape
that existed was destroyed by the melting glacial ice sheets. To speculate: if there had
been no melting ice sheets, I believe the Philadelphia region would stand several hundred
feet higher above sea level." Presently, the Naval Yard is 10 feet above sea level,
Matthias Baldwin Park 50 feet above sea level and Chestnut Hill 445 feet above sea level.
"Without the flooding, there would be no Delaware nor Schuylkill Rivers, no Pennypack,
Tacony and Wissahickon Creeks. There would have been an earlier river that no longer
exists." Gosh, I like Philadelphia's terrestrial footprint just as it is. I call it home.

The crustal plates of Earth undergo cycles of collisions and separations. About 335 million years ago, the ancestral continents of Africa and North America slowly smashed into each other, folding the crust into mountain ranges: the Appalachians in current Pennsylvania and the Atlas Mountains in current Morocco. These mountains were originally as high as the Rocky Mountains (or some say the Himalayas). The valleys between the folds channel the rivers in a predominantly north-south direction.
Over the last 2.5 million years, there has been an advance of continental ice sheets from each pole towards the equator roughly every 100,000 years. The image shows the extent of the last ice sheet which diminished 10,000 years ago. These ice sheets were up to 1.6 miles thick, tying up water in their ice and thereby lowering ocean water levels. Baldwin Park would have been 400 feet above sea level, instead of its current 50 feet above. The ice sheet shown extends as far south as Boulder Field at Hickory Run State Park, a glacial formation north of Philadelphia in northeast Pennsylvania.
These moving ice sheets erode surface features, and the massive amounts of water released on melting shape the land and river patterns.
authored by Sandra Owens, December 2019
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