Saturday, September 15, 2012

Communities of Interest

Last week I was invited to collect fossils for the first time along Scientists’ Cliffs on the western shore of the Chesapeake Bay.  This is a rare treat for fossil hunters who don’t own property here (and don’t kayak) because the only access to the beach from the land side is across private property.

At these cliffs, part of the Calvert Cliffs, the dominant formations are middle Miocene (roughly 16 to 12 million years old).  The fossil material found here is likely to be a bit younger than what I find about 10 miles to the north (a couple of miles below Chesapeake Beach, Maryland) where I usually hunt.  In general, as one moves south down the Bay, the older (lower) formations sink beneath the beach and the younger (upper) formations make up more of the exposed cliffsides.

If I’d done my homework I would have expected to find some fossils here different from my usual suspects.  But, to be honest, I only anticipated a greater abundance of the same, assuming these beaches were not as scoured by collectors as those further north.  (I was wrong about that.)  The beach itself really doesn’t appear dramatically different at first glance, slumping cliffside here seems like slumping cliffside to the north.

But there are some telltale signs that things are actually very different.  For one, the cliffsides here don’t generally reach the heights they do to the north.  Certain familiar layers in the cliffs are dramatically thinner here or no longer even visible.  Yes, indeed, age and distance make a difference.  To the north, many of fossils are eroding out of the older Calvert Formation, while here the younger Choptank Formation plays a much stronger role in creating the community of fossils protruding from fallen blocks of clay and the gray sand on the beach, or swirling in the wash.  In both locations, Calvert and Choptank layers are exposed, so, neither contributes exclusively at one place or the other, but a much greater proportion of the northern cliffs are Calvert, while 10 miles south, the Choptank predominates.  Indeed, most of the Calvert has disappeared.  (Detailed information on the exposure of these formations along the Calvert Cliffs can be found in Stratigraphy of the Calvert, Choptank, and St. Marys Formations (Miocene) in the Chesapeake Bay Area, Maryland and Virginia, by Lauck W. Ward and George W. Andrews, Virginia Museum of Natural History, Memoir Number 9, 2008.)

The picture below captures a small segment of the fossil invertebrate faunal community I found along the Scientists’ Cliffs shore.

The centerpiece of this picture is the mollusk Chesapecten nefrens Ward and Blackwelder.  Though penetrated in places (by predators?  by being battered in the waves?) and marked by barnacles, this is a wonderful specimen because, despite its travails, its perimeter is complete.  To give a frame of reference for the sizes of this and the other fossils in the picture, the C. nefrens measures slightly more than 4.5 inches from top to bottom.  Though C. nefrens is common along the shores of the Calvert Cliffs, this specimen is much larger than any I’ve collected further north.  Harold E. Vokes et al., in Miocene Fossils of Maryland (2nd edition, Maryland Geological Survey, 1999), confirm this size difference between specimens from the Choptank Formation and those from the Calvert.  Further, they observe that Choptank specimens frequently appear with many large barnacles attached to them.  (Though I was guided by Vokes et al., any errors in the identification of this shell and the other specimens in this post are mine alone.  Corrections appreciated.)

At the bottom left in the picture is a small segment of an echinoderm (in this case a “sand dollar”) named Abertella aberti (Conrad).  Vokes et al. describe this animal as common in the Choptank, but typically found broken.  Like a pottery shard, this piece of sand dollar only hints at the grace and complexity of the patterns that adorn the entire surface of the A. aberti.  Below is a close-up of the A. aberti fragment and the drawing of the entire echinoderm that appears in Miocene Fossils of Maryland.

Continuing clockwise are two examples of the mollusk Anadara staminea (Say), not one I’d found in the north, and probably with good reason.  According to Vokes et al., A. staminea is “known only from the Choptank.”

At the upper left is a single example of what I believe is a Balanus concavus Bronn, one of the large barnacles (though this one isn’t particularly impressive) often adorning the shells of C. nefrens.  Barnacles hold a certain fascination for me because, most surprisingly, the animals creating these shells are crustaceans.

Finally, at the lower right corner of the picture, is a damaged example of the gastropod Ecphora tricostata Martin.  I have found these at times up north and so it makes sense that Vokes et al. write that this species is commonly found in the Calvert Formation.  They do note that is rarely discovered in the lower Choptank, so, perhaps the small block of clay in which this specimen was encased came from the Calvert layer still exposed here at Scientists’ Cliffs.

The beach offered me a distinctive community of invertebrates.  There is another distinctive community here.  Well, actually, up above me on the wooded, rolling land that stretches back from the cliff edge.  In the mid 1930s, G. Flippo Gravatt and his wife Annie Gravatt, both scientists with the U.S. Department of Agriculture, purchased 238 acres of land here.  They were on a mission to create “a colony for scientists and professional people of kindred spirit.”  (Shawn White, Scientists’ Cliffs:  An Abbreviated History, April 15, 2009.)  The site held myriad charms for the Gravatts, among them the fossils eroding from the cliffs.  But perhaps more attractive to Flippo Gravatt were the chestnut trees.  He had worked on the pathologies attacking the American chestnut tree and was one of the first scientists to breed these trees.  He “picked the land partly because it boasted a few surviving chestnut trees, and he built his own cabin there from chestnut logs.”  (American Chestnut:  The Life, Death, and Rebirth of a Perfect Tree, by Susan Freinkel, 2007, p. 148.)

In the autumn of 1935, the Gravatts and some colleagues dedicated the site, deciding to name it Scientists’ Cliffs, though that wasn’t the only name attached to it.  According to the history of the colony, Annie Gravatt anointed it “Flippo’s Folly.”  Several cabins were soon built, available initially for rent during the summer.  A more permanent colony emerged quickly with purchases of plots and the cabins.

From the outset it was intended to be a very select community.  Under the constitution and bylaws of the Scientists’ Cliffs Association, incorporated in 1937, only scientists could be members.  According to Susan Freinkel, that meant folks with PhDs.  “Later this was broadened to include all college graduates and then extended to those who had achieved recognized status in their profession without college degrees.”  (Scientists’ Cliffs:  An Abbreviated History.)

Management of the community evolved over time as an increasing number of people came to live here year round and infrastructure and other needs multiplied.  A Community Administrator is now responsible for addressing the quotidian needs of residents.  But the twice annual meetings of the Association, at which issues are discussed and decided, continue, thus ensuring the persistent of “[e]ssentially the atmosphere of a New England town meeting.”  (Scientist’s Cliffs:  An Abbreviated History.)

And then there’s the physical layout of the community, a wonderful mixture of cabins and houses nestled among the trees along winding roads.  Nature still predominates.  Curiously, though, I thought of St. Mary Mead, the home of Agatha Christie's Miss Marple.  No, Scientists' Cliffs is not an idyllic English village in appearance, but I had the same sense of this community as I do when contemplating the map of St. Mary Mead that appears in the Miss Marple mysteries - at its best, it offers a kind of sanctuary.  I suspect, as well, that, regardless of where in the English countryside Christie intended the community of St. Mary Mead to be located (about which there is some debate), fossils would be there, too.

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