Swatara State Park sits between and on parts of Second and Blue Mountains in the larger Appalachian Mountains.  It encompasses much of the Swatara Creek, which carved one of the best examples of a water gap in Pennsylvania - Swatara Gap - during the Tertiary.  The rocks underlying Swatara are mainly of Ordovician, Silurian, and Devonian age (354-490 million years old), and were folded into mountains during the Alleghanian orogeny.

The first area of interest is the Late Ordovician Martinsburg Formation, made of mudstone and siltstone.  The sediments that make up the Martinsburg Formation were deposited over 440 million years ago in a sunlit shallow sea.  There was not much disturbance of the soft seafloor, but enough sediment was deposited to preserve many examples of the organisms that lived there.  One of the most famous organisms preserved in these sediments is the trilobite Cryptolithus bellulus (see drawing, left).

A trilobite is an ancient arthropod that got its name from the three lobes that run down its body (tri-lobe-ite).  It is made of three main body parts: a cephalon (head), a thorax, and a pygidium (tail piece).  Trilobites also have multiple body segments and jointed legs.  Although they are extinct now, trilobites were very successful and existed for the entire Paleozoic era, or over 300 million years!   At Swatara you will find small trilobites that range from only a few millimeters to a few centimeters in length, but trilobites have been found around the world that are up to 72 centimeters long!

When you arrive at the fossil pit, the easiest place to start looking for fossils is in the rock that has been dumped in the middle of what used to be only a gravel parking lot (see photo, right).  The original location of this material was at the intersection of the rt81 overpass and rt72.  Fossil hunters removed so much material from under the rt81 overpass that the site was declared off limits.  Fortunately, as construction began on a new overpass in 2004, the debris containing fossils was taken to its new location at the fossil pit so that enthusiasts could once again enjoy hunting for fossils.  Unfortunately, the original location has since been covered in building materials and limestone to prevent erosion, and you can no longer even see the original beds.

After checking out the loose rock in the middle of the Swatara fossil pit, move to the edge where the rock is still in its original position (mostly, except where 4-wheelers have disturbed it).  These rocks are the original reason why this location is called the Suedberg fossil pit.  You may need to use a little more effort looking for fossils here, but it will be worth it.  As mentioned above, these fossils are focused into 2-3 inch thick lenses.  Once you find one of these layers, carefully examine the rock and break it apart to expose more fossils.  I do not have any examples to show you from this site, but the image on the left will show you drawings of fossils you can expect to find, such as brachiopods, crinoids, and the elusive Phacops rana.  One interesting difference between the two types of trilobites that you can find in Swatara is that Cryptolithus bellulus had no eyes, but Phacops rana had quite complex compound eyes.

SOURCES USED TO WRITE THIS PAGE

Gon III, Sam.  2005.  A Guide to the Orders of Trilobites.  http://www.trilobites.info/

Hoskins, Donald M., and Royer, Denise W.  Revised 1997. Pennsylvania Trail of Geology: Swatara State Park; Park Guide #16.  Pennsylvania Geological Survey.

Lehmann, David. The Paleoecology of the Swatara Gap Fauna.  Pennsylvania Geology, v. 19, no. 1, February 1988.

Wicander, Reed, and Monroe, James S. 2004. Historical Geology (4th ed.).  Thompson Learning, Inc.  Canada.

http://www.dcnr.state.pa.us/topogeo/collecting/state_fossil.aspx.  2005.  The State Fossil.  Pennsylvania Department of Conservation and Natural Resources.

http://www.dcnr.state.pa.us/topogeo/collecting/swataragap.aspx.  2005.  The Swatara gap Fossil Migration.  Pennsylvania Department of Conservation and Natural Resources.