Don't Get Caught in the Midden!

Kathleen Nolan
St. Francis College
Brooklyn, NY

knolan@stfranciscollege.edu

"Why are these oyster shells here?" I asked myself during one of my long jaunts with Maggie, my dog, in Riverdale Park, Bronx, New York. This overgrown "natural" woodland, owned by the City of New York, is on a two-mile elevation adjacent to the Hudson River. A neighbor, Mike, offered, "Oh, those are from seagulls dashing them against that cement abandoned well." An internal voice told me otherwise, as I noticed whole unbroken shells poking up through the earth, especially after a rain. One day I squatted down and started digging in the dirt with a stick. Piles of muddy intact shells (some crumbling) were buried here! These were no recent shells transported here by seagulls! Also, I knew anecdotally that researchers were trying to re-introduce the oyster to the Hudson, which told me that there weren't too many there presently, if at all.  

My mind harkened back to the times in Florida during Easter vacations that my father would drive us to Turtle Mound, an ancient place on the Canavral National Seashore. The mounds are composed of oyster shells, thought to signify grave markers for the Techumseh Indians.   Perhaps the Bronx shells were left there by Native Americans as well. I started researching "shell piles" and discovered that they were called "middens" or waste heaps. I meandered around on some of the side trails in Riverdale Park and noticed shells throughout the park, but found three concentrations of them that I named Midden 1, 2 and 3. I collected over 200 of these and gave them to a few students to clean, measure, and weigh. I sponsored a Saturday "field trip" in which the students took the commuter Metro North Rail Road to Sputen Duyvil where I live, and that is one-half mile south of the park. After they helped me dig up and collect more shells, I gave them lunch in our apartment where they enjoyed views of the Hudson River.  

I felt that these shells would provide a good opportunity to teach the students statistics such as mean, standard deviation, and correlation (Is there a correlation of length with mass?). The students presented a poster of their measurements at the Northeast Natural History Conference in Albany, NY in April, and I decided to try to ascertain the actual age of the shells. One of the students, Tara, had found a report that stated that they were from the Late Woodland Period, 3000-4000 years ago. The authors surmised this by associated artifacts, such as "bifaces" (stone tools). I did not find any published radio-dates of these shells.

Well, with my normal procrastination, I didn't get around to mailing the shells to Beta-Analytic in Miami, Florida for dating, till July. (At $300 per shell I found it was difficult to part with my grant money!) In the meantime, I read the "Big Oyster" by Mike Kowsky, who mentioned that shell middens left by the Lanape Indians in Dobbs Ferry, thirteen miles north of me, were 6000 years old. I read the book furtively, praying that MK wouldn't mention Riverdale Park oysters. (In a typical selfish scientist fashion, I wanted this to be MY discovery!) There was a mention of Spuyten Duyvil oysters, but no note of any shells from the park.    

Thus I was both relaxed and elated when I received my e-mails from Beta-Analytic last week stating that the six shell samples I mailed them were all over 2000 years old. The company used C14 dating with a C13 correction. The later is done by comparing the ratio of C13 to C12 in a mass spectrophotometer. The accuracy is supposed to be plus or minus 70 years.  

I am pondering what to do with this information. Should I tell the local press? Wouldn't that cause a lot of unwelcome diggers in my park? I will most likely call the natural resources division of the NYC Parks Department, as Riverdale Park is a New York City Park. I think some type of memorial should be erected to the Native Americans that once lived there, with perhaps a plexiglass covered exhibit of the shells.  

References
Kurlansky, M. 2006. The Big Oyster: History on the Half Shell. Ballantine Books, New York.  

Nolan, K., Glover, T., Phoolbosseea, M, Charles, F, Amedee, K, and S. Williams. 2006. Oyster middens in Riverdale Park. Poster presented at: Nature in the City Symposium, Long Island University, March, 2006; Northeast Natural History Conference at the New York State Museum, April 20, 2006, Laboratory Open House at SFC, April 27, 2006.