Philadelphia fossils and ferns

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Paul Murdoch and Clay Carkin (USA)

Our hectic, 48-hour adventure had its beginning many years ago, courtesy of the WWW. My friend, Clay, a sixth grade science teacher in Freeport, Maine, had originally contacted the Calvert Marine Museum fossil club’s website about purchasing fossils to use in his classroom. Although I live outside of Philadelphia in Pennsylvania, I visit the Calvert County Maryland area quite frequently and have a keen interest in the fossils there.

Clay and I chatted a few times, and I subsequently agreed to stop by his school and do a fossil presentation. We also discussed going fossil hunting together. However, our schedules never worked until this year.

Clay will tell you that Maine is a poor state to live in, if your passion is fossil collecting. Therefore, he and I planned a 48-hour blitz of the better-known fossil localities within a 100 mile or less radius of my home. My wife and I met Clay and his wife Joye at the airport at noon on Friday and, immediately, Clay and I set off to some fossil-hunting grounds. On Friday, the first and only stop for Clay and me was a trip up I-95 and the New Jersey turnpike to the Cretaceous outcrops of marine fossils in the brooks of Monmouth County, New Jersey.

After a short detour due to road construction, we were in the Ramanesson Brook, sifting through the sand and pebbles and finding sharks’ teeth. Clay was a natural, finding a shark’s tooth, Squalicorax sp (crow shark) on his very first sift. My find for the day was a complete Ischyriza sp (saw fish) tooth. We only had a few hours of sunlight and by 4:30pm we had to call it a day. All of the finds (about40 teeth in all) were given to Clay, so that he could assemble them for a classroom display.

My vicarious activity for students to get a feel for what it is like to collect specimens consists of sifting for gems and fossils in the classroom environment. Now, I can say I have done the real thing and successfully found some nice sharks’ teeth. The unusual Squalicorax was a bonus, to say nothing of having a video ready for my class on Monday.

Some of our finds can be seen in Fig. 1, which shows the range of sharks’ teeth that can be found in the Ramanesson Brook area.

Fig. 1. Sundry shark species.

The next day, we departed at 5:30am for a trip to the anthracite coal regions of Pennsylvania. Our first stop was the world-famous fossil fern locality of St Clairin Schuylkill County. In fact, it is a type locality for what, in the USA, is known as the “Pennsylvanian period” (325 to 286Ma). (It is known as the “Upper Carboniferous” in the UK.) This locality produces abundant fern fossils located on wavy plates of shale. The wavy nature makes the fossils extremely brittle and hard to extract. This site would be incredible if the shale broke in a clean, slate-like pattern, but that’s just not how it is.

Fig. 2. An unknown plant fern.

However, the ferns are preserved in amazing detail. The organic material of the leaf matter was probably replaced by pyrite (from sulphides). Then, as the sediments piled up and the temperature and pressure became greater, pyrophyllite (aluminium silicate, a whitish mineral) is believed to have replaced the pyrite. This chalky-white coating is what makes ferns from this site so distinctive and obvious throughout the world, even to the casual collector. Occasionally, beetles, spiders, mosquitoes and other insects are discovered mixed in with the ferns.

Fig. 3. Alethopteris sp.

The site is about a one-mile walk into the woods and it served to warm us up, as it was the first day of the fall season and there was a hard frost on the ground. A friend of mine took us to his favourite spot for these fossils and the area was just littered with them. It was the fossil equivalent of shooting fish in a barrel. In less than three hours, we had numerous species and specimens ready to wheelbarrow back to the truck. I estimated that we found at least six different species of fern. The most common were Alethopteris, Neuropteris and Pecopterisa, which can be found stacked upon themselves in such abundance that it becomes impossible to distinguish them individually.

Fig. 4. Pyrophyllite (a white mineral coating) on these St Clair (PA) fossils (Alethopteris sp) gives that distinctive look that is characteristic of this world class collecting locality.

After about three hours at the site, we had four, five-gallon buckets crammed with pieces to give away, and we were ready to head back in time to our next destination – theDevonian.We backtracked to the southern end of Schuylkill County to a site near the Auburn/Deer Lake area. This site has the potential to be another ‘fish in a barrel’ spot, this time not for ferns but for brachiopods (marine shellfish) and other invertebrates. However, this depends on finding the narrow, brownish-coloured band they are preserved in. As luck would have it, a recent excavation had uncovered a plethora of fossils and three more five-gallon buckets for fossil goodies were packed into the truck.

This concluded our fossil hunting for the weekend, but we are far from done exploring together.

Shark teeth images by Stuart Handley ©. Other images by Clay Carkin and Paul Murdock.

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