Coal Mine Classic 2014: Cumberland Valley/Ridge and Valley
This is a prologue to my short trip today, which will be lengthened by stopping to look at some of the interesting sites described in the Roadside Geology of Pennsylvania (B. B. van Diver, 1990, Mtn. Press, Missoula, Montana).
I will be passing through a Karst topography (sinkholes, pinnacles, and springs) from the MD line to mile 17 with the northern terminus of the Blue Ridge to the east. This ridge extends to GA and I have followed it on the previous day. I hope to find Pine Grove Furnace, which was used to produce iron from low-grade ore (limonite). Here is a picture of one of the pinnacles in a corn field.
It is the white object. There were others but pics were hard to take from the interstate. I found the sign to Pine Grove Furnace and made a detour to see either the limonite, quartzite, and/or fossils. Here is an image of the lake near the quartzite. These lakes were created all over PA during the depression by the WPA; they are very popular for weekend outings.
I hiked about 1 mile up a steep grade to get these great images of the area and the Precambrian quartzite that was brought to the surface by the tremendous horizontal pressure and resulting uplift of the Appalachian/Alleghenian orogeny when Africa collided with N. America.
This is called “Steeple Pole” but don’t ask me why. It is a highly metamorphosed sandstone that was probably? deposited in either a beach or sand dune environment more than 1.5 billion years ago, which were metamorphosed BEFORE the Appalachian orogeny occurred (~400 my). This stuff is really HARD!
I also found something I didn’t expect to, some fossil burrows from worms (not known in the modern world) in ~400 my sandstones. The first image shows the surface of what would have been the seafloor (shallow) when the creatures were alive.
This image shows a section perpendicular to the seabed. The worm holes are quite visible because it sprinkled while I was hiking and water is excellent for exaggerating the contrast (remember the entrance to Cibola in National Treasure: Book of Secrets?
I didn’t make it toReservoir Park on US 22 for a good view of a water gap through the ridge because I was so hot and tired from the uphill hike to see Steeple Pole that I wanted to stay in the ACd truck! After crossing I-78, I hope to collect some Ordovician (~500 my) fossils at Swatara Gap, and then some Devonian (~400 my) fossils at Suedberg. From there to the campground, there is a good roadcut that shows coal beds in the Catskill Fm. The guide book I have is 30 years old and these fuzzy images of (maybe) brachiopods from the Devonian section are the best I could find before getting to the camp site.
The linear features in the middle are on the shell of a clam in modern benthic invertebrates. These are certainly not modern. I need to start taking the better camera along.