Landforms seen along SEPTA’s Norristown High Speed Line

Authors

Introduction:

Trains on the Norristown High Speed Line (NHSL) require approximately 30 minutes to travel 13.4 miles from SEPTA’s 69th Street Terminal to the Norristown Transportation Center, yet that relatively short trip involves crossing several creeks and a major river, climbing up and down as several drainage divides are crossed, passing through a water gap, and traveling over a variety of different bedrock units. This guide describes on a stop-by-stop basis visible landforms in the sequence they are observed assuming the observer begins at the 69th Street Terminal. The one and two car trains have large windows that make observations easy, but be aware stops are only made if passengers want to board or get off and some stop locations, while having platforms, are not well labeled.

69th Street Terminal-Parkview

The 69th Street Terminal is built on the 100-foot contour line and while not visible from the Terminal Cobbs Creek is flowing in a valley approximately 50 feet lower just to the north. East of the 69th Street Terminal southeast oriented Cobbs Creek flows from the Piedmont Province and turns to flow in a south direction along the boundary between the Piedmont Province and the Atlantic Coastal Plain, which today has been significantly altered by urban development. The 69th Street Terminal is located near the mouth of deep valley Cobbs Creek has eroded into the Piedmont Upland. Probably the entire region had an elevation at least as high as the present day Delaware River-Schuylkill River drainage divide elevation crossed by the NHSL just beyond the Radnor stop (approximately 450 feet today). From the 69th Terminal the NHSL travels in northwest direction up the Cobbs Creek valley with Cobbs Creek located on northeast (right) side and Cobbs Creek Park and Golf Course across the creek. Weathered bedrock exposures seen in cuts along the track are mapped as Wissahickon Formation mica schist of probable lower Paleozoic age.

Parkview to Township Line Road (West Overbrook)

The NHSL track is located in the Cobbs Creek valley and Cobbs Creek and Park and Golf Course continue to be seen on the northeast (right side). Philadelphia Electric Golf course is seen on southwest (left side just before leaving the Philadelphia city limits. Before reaching the Philadelphia Electric Golf Course the track crosses the boundary of mapped Wissahickon Formation mica schist and enters a region of mapped granitic gneiss and granite of probable lower Paleozoic age. The contact may be a fault line and a minor south-southwest oriented tributary valley seen in the golf course on the northeast (right) side of Cobbs Creek may be eroded along that fault line. Weathered bedrock exposures can be seen in cuts along the track.

Township Line Road (West Overbrook) to Penfield (Manoa Road)

Cobbs Creek and Cobbs Creek Park on are located on the right side (northeast) of the track. Most of the distance between Township Line Road and Penfield is traveled over mapped granite gneiss and a zone of mafic gneiss, although shortly before reaching the Penfield stop the underlying bedrock is again the Wissahickon Formation mica schist. Again weathered bedrock exposures can be seen in cuts along the tracks. The mica schist, granite gneiss and mafic gneiss are all mapped as being of probable lower Paleozoic age, which was a time when the Philadelphia region was experiencing intense crustal compression and probable mountain building. Rocks underlying the Piedmont Upland today are usually interpreted to be eroded roots of that mountains formed at that time. The contact between the granite gneiss and the mica schist may again be a fault line.

Penfield (Manoa Road) to Beechwood-Brookline

The NHSL track continues in the Cobbs Creek valley with the creek located on the northeast (right) side. Bedrock from Penfield to Garrett Hill is the Wissahickon Formation mica schist usually mapped as being probably lower Paleozoic in age. Weathered outcrops are visible where the NHSL route has been cut into the valley wall. The Wissahickon Formation mica schist is an erosion resistant material and Cobbs Creek crosses the 150-foot contour line at Penfield. Adjacent hills today rise to more than 300 feet and the entire region was probably at least 150 feet higher than those hill tops at the time the Cobbs Creek valley erosion began. The amount of erosion that has occurred and the depth of the Cobbs Creek valley suggest the Cobbs Creek valley was eroded by vast quantities of water from outside the present day Cobbs Creek drainage basin.

Beechwood-Brookline to Wynnewood Road

The NHSL crosses Cobbs Creek about midway so at Wynnewood Avenue Cobbs Creek is located on the left (southwest) side of the tracks. At the point where the NHSL crosses Cobb Creek the elevation is approximately 250 feet or 150 feet higher than at the 69th Street Terminal. The track will continue to climb to higher elevations as it follows the Cobbs Creek valley headward until crossing the Cobbs Creek-Meadowbrook Run drainage divide near the Bryn Mawr stop.

Wynnewood Road to Ardmore Junction

The NHSL is still climbing in Cobbs Creek valley with Cobbs Creek located on the left (southwest) side. Note how Cobbs Creek has been channeled to flow between the tracks and the houses on the opposite side of the channel. After the point where the channeled section ends there are houses located between the track and Cobbs Creek. The track will be adjacent to the Cobbs Creek headwaters again after the Ardmore Avenue stop.

Ardmore Junction to Ardmore Avenue

Just before reaching the Ardmore Avenue stop Cobbs Creek will again become visible to the left (southwest) as the track continues up the Cobbs Creek valley. The track is located in the Cobbs Creek valley and is climbing gradually to an elevation of 300 feet. Hills on either side of the valley rise approximately 50 feet higher.

Ardmore Avenue to Haverford

The NHSL crosses the 300-foot contour line at Ardmore Avenue and Cobbs Creek crosses the 300-foot contour line a short distance upstream from Ardmore Avenue. Cobbs Creek at that point is more than 250 feet higher than it was near the 69th Street Terminal and the NHSL is 200 feet higher than it was at the 69th Street Terminal. Cobbs Creek and Merion Golf Course are located on left (southwest) side. Cobbs Creek at this point is quite small as the track is nearing the Cobbs Creek headwaters. Haverford College campus is located to the northeast (right).

Haverford to Bryn Mawr

The NHSL is proceeding up the Cobbs Creek valley with the Cobbs Creek headwaters being located on the left (southwest). The NHSL crosses the 350-foot contour line and then climbs to the Bryn Mawr stop, which has an elevation of slightly less than 400 feet. The Bryn Mawr stop is located in a cut across the divide separating southeast oriented drainage to Cobbs Creek and drainage to southwest oriented Meadowbrook Run, which flows to Ithan Creek and then to Darby Creek. At the Bryn Mawr stop the NHSL is 300 feet higher than it was at the 69th Street terminal. The Wissahickon Formation mica schist continues to be mapped as the underlying bedrock although urban development and vegetation hide almost all bedrock exposures.

Bryn Mawr to Roberts Road (Rosemont)

Track is on upland adjacent to the Cobbs Creek-Meadowbrook Run drainage divide, although it is descending slightly into the Meadowbrook Run valley and has an elevation of approximately 370 feet at the Roberts Road (Rosemont) stop.

Roberts Road (Rosemont) to Garret Hill

After leaving the Roberts Road (Rosemont) stop the northwest oriented NHSL descends to approximately 350 feet and then begins to climb again as it crosses the deep southwest oriented Meadowbrook Run valley. Meadowbrook Run is flowing under the track at an elevation of between 320 and 330 feet. Meadowbrook Run drains in a south-southwest direction to Ithan Creek, which then flows to southeast oriented Darby Creek. Meadowbrook Run originates in Rosemont, a short distance to the northeast of the NHSL, on the southwest side of one of the deepest wind gaps notched into the Delaware River-Schuylkill River drainage divide. Before being altered by railroad and highway construction the wind gap floor probably had an elevation of between 360 and 370 feet with drainage divide elevations on either side rising to more than 430 feet. North of the wind gap is the east, south-southeast, and north-northeast oriented Mill Creek valley, which drains to the southeast oriented Schuylkill River. The Meadowbrook Run valley and the wind gap are located along the mapped contact of the Wissahickon Formation mica schist (often considered to be lower Paleozoic in age) and felsic gneiss of Precambrian age (on northwest side of valley). The contact is probably a fault line and a zone of more easily eroded material than the erosion resistant Wissahickon mica schist and the felsic gneiss on either side.

Garret Hill to Stadium (Ithan Road)

At Garrett Hill the NHSL has reached an elevation of more than 420 feet and then descends slightly as it crosses the headwaters of southwest oriented Kirks Run, which drains to Ithan Creek. The NHSL in this area is approaching the Delaware River-Schuylkill River drainage divide, which is located a short to the northeast (on the right side of the track), and which crosses the Villanova University campus.

Stadium (Ithan Road) to Villanova

The NHSL track curves so it is oriented in a west-northwest direction and is nearly parallel to the nearby Delaware River-Schuylkill River drainage divide. The low hill to the north on which several Villanova University buildings are located is the drainage divide location.

Villanova to Radnor

The track descends slightly before curving to the north as it crosses Spring Mile Road and the Browns Run valley. Browns Run is a Hardings Run tributary, with Hardings Run flowing to Ithan Creek, which then flows to Darby Creek. At one time a NHSL branch continued in a west-northwest direction from this curve to reach Main Line suburbs further to the west. Spring Mile Road can be identified by newly constructed commercial developments seen to the northeast of the track. After crossing Spring Mile Road and Browns Run the NHSL crosses a low drainage divide into the Hardings Run valley and crosses Hardings Run at the Radnor stop. At the Radnor stop the NHSL track has an elevation of approximately 380 feet.

Radnor to County Line

Shortly after leaving the Radnor stop the NHSL route begins to climb as it travels underneath the former Pennsylvania Railroad main line and now the Amtrak Harrisburg line and SEPTA Paoli-Thorndale line and then enters a deep cut as it crosses the Delaware River-Schuylkill River drainage divide. The Pennsylvania Railroad built its main line in this location near the Delaware River-Schuylkill River drainage divide to avoid ups and downs of the stream valleys draining both sides of this major divide. However, because shallow wind gaps are notched into the drainage divide the former Pennsylvania Railroad line crosses from one side to other. Further to avoid ups and down the Pennsylvania Railroad used fill to construct embankments across the heads of valleys and the shallow wind gaps. The embankment where the NHSL goes under the former Pennsylvania Railroad main line was constructed across the head of a short Hardings Run tributary valley draining in a southwest direction from the shallow wind gap where the NHSL crosses the Delaware River-Schuylkill River drainage divide at an elevation of between 430 and 440 feet or approximately 340 feet higher than the 69th Street Terminal.

Shallow wind gaps crossing the Delaware River-Schuylkill River drainage divide, such as the shallow wind gap used by the NHSL, are evidence that water once flowed from the present day Schuylkill River (Gulph Creek) drainage basin to the north into the Delaware River (Darby Creek) drainage basin to the south. At that time valleys in the Schuylkill River drainage basin (including the Schuylkill River valley) had not yet been eroded and the water was eroding the Darby Creek and tributary valleys. NHSL builders deepened the shallow wind gap floor with the cut seen just after passing under the former Pennsylvania Railroad main line. In that deep cut the NHSL begins to descend into the Gulph Creek valley. The descent is first made along a Gulph Creek tributary valley before reaching the County Line stop (elevation about 330 feet).

County Line to Matsonford

The NHSL track crosses the divide between two north oriented Gulph Creek tributaries as it descends along the Gulph Creek valley south wall to the Matsonford stop. Weathered bedrock seen in some of the cuts as the track descends into the Gulph Creek valley is mapped as felsic gneiss of Precambrian age, although a narrow band of Wissahickon Formation has been mapped near the Matsonford stop. Bedrock underlying the Gulph Creek valley is mapped as a narrow band of Conestoga Limestone of Cambrian and Ordovician age. Bedrock making up the hills on the north side of the Gulph Creek valley is mapped as Octoraro Formation phyllite of probable lower Paleozoic age. The limestone is much easier to erode than the Wissahickon Formation mica schist and the felsic gneiss and the contacts between the different bedrock units may be fault lines.

Gulph Creek flows in a east-northeast direction to near the Matsonford stop location in the valley underlain by the Conestoga Limestone, but just before reaching the NHSL route Gulph Creek turns abruptly to leave the Conestoga Limestone floored valley and to flow through a deep water gap eroded across the high ridge of Octoraro Formation phyllite. The deep Conestoga Limestone floored valley continues in an east-northeast direction from the Matsonford stop location to the Schuylkill River and logically Gulph Creek should continue to flow in that valley. However, Gulph Creek ignores the presence of that limestone-floored valley. A low drainage divide with an elevation of between 230 and 240 feet, just east of the Matsonford stop, separates the east-northeast and north oriented Gulph Creek valley from local east-northeast oriented drainage to the Schuylkill River. In other words the limestone-floored valley is today a through valley drained by different streams. The Octoraro Formation phyllite ridge across which the the Gulph Creek water gap has been eroded exceeds 410 feet in elevation.

Matsonford to Gulph Mills

After leaving the Matsonford stop the NHSL track almost immediately enters the narrow Gulph Creek water gap and Gulph Creek can be seen on the left (west) side. The water gap was probably eroded by a very different stream than one seen today. The narrow water gap valley is more than 200 feet deep and is eroded across a ridge exceeding 410 feet in elevation. Just north of the water gap near the Gulph Mills stop Gulph Creek enters another Conestoga Limestone floored valley and turns to flow in an east-northeast direction to reach the Schuylkill River. An interesting question is why does Gulph Creek turn in a north direction to flow through the deep water gap when it could have continued in an east-northeast direction at Matsonford without having to cross the 410-foot plus high Octoraro Formation phyllite ridge? Contacts between the Octoraro Formation and the Conestoga Limestone on both sides of the high ridge may be fault lines, although there is no mapped fault located along the water gap route.

Gulp Mills to Hughes Park

After leaving Gulph Mills the NHSL climbs out of the Gulph Creek valley and first crosses headwaters of northeast oriented Matsunk Creek (the Gulph Mills Golf Course is located on the right or east side) with Matsunk Creek flowing to the Schuylkill River as a barbed tributary. Bedrock between Gulph Mills and Hughes Park is limestone mapped as the Conestoga Formation of Ordovician and Cambrian age although at the crest of the drainage divide the track crosses a narrow band of Octoraro Formation phyllite, which is usually considered to be lower Paleozoic in age. The Octoraro Formation is more erosion resistant than the Conestoga Formation limestone, which is why a low ridge is present just before reaching the Hughes Park stop. After crossing the Octoraro Formation ridge the track descends to the Hughes Park stop and into the Chester Valley northeast end.

Hughes Park to Dekalb Avenue (King Manor)

After leaving Hughes Park the NHSL passes under the Pennsylvania Turnpike and a large limestone/dolomite quarry can be seen on the left (west) side. Bedrock that was being quarried is the Ledger Formation dolomite of Cambrian age. Dolomite is a carbonate like limestone and like limestone in humid climates is easily eroded and can be dissolved and is often found on valley floors (in arid climates limestone and dolomite often form ridges). The ability of water to dissolve the carbonates can result in the formation of caves and sinkholes, which produces what is called a karst landscape. The broad carbonate-floored valley crossed by the NHSL from the Gulph Mills stop to the quarry is the east-northeast end of the Chester Valley. There are sinkholes in the Chester Valley including some near the NHSL, although they are not readily visible from the NHSL.

After leaving the quarry area the NHSL crosses another geologic contact (probably a fault line) from the Ledger Formation into the Stockton Formation of Triassic age. The Stockton Formation includes red sandstone and shale and weathered exposures of red sandstone and shale can be glimpsed in cuts along the NHSL track just beyond the quarry and before reaching the Dekalb Avenue (King Manor) stop.

Dekalb Avenue (King Manor) to Bridgeport

From the Dekalb Avenue stop the NHSL descends approximately 100 feet into Bridgeport as the track approaches the Schuylkill River.

Bridgeport to Norristown Transportation Center

The NHSL crosses the southeast oriented Schuylkill River on a high bridge offering excellent views of the valley and the towns of Bridgeport and Norristown. The low Norristown Dam is located just upstream from the bridge and can be seen on the left (west) side. The island just upstream from the dam is Barbadoes Island.

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