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Local science writers look for fossils on a block of stone that is part of the Duke Ellington Bridge.

This past Saturday, geologist Callan Bentley, of Northern Virginia Community College, led a couple of dozen local science writers on a trip back through Washington, D.C. history. We didn’t learn about Abe Lincoln or George Washington, though. This was geological history, a record of events that occurred hundreds of millions of years ago.

An interesting tangent to our field trip took place on the Duke Ellington Bridge as we walked across Rock Creek Park. The bridge, like many of Washington’s structures, is made of blocks of stone (often from faraway states; Indiana in the case of the bridge). These blocks, Bentley pointed out, are often full of fossils. You just have to look for them. (But a little knowledge is probably helpful; I never would have spotted the fossils on the bridge if Bentley hadn’t been pointing them out to us.)

A close-up shot of the fossil-bearing bridge block.

It seems a person could take a really interesting tour of geological history without ever stepping inside a museum here in Washington. If you don’t believe me, check out dcfossils.org. A local geology enthusiast, with help from people like Bentley, has been cataloging Washington’s architectural fossils—fossils that can be found in the building blocks that are part of buildings, monuments and bridges—photographing them and writing about the locations and the fossils you’ll find there. The blocks that make up the National Museum of the American Indian, for example, are made of Kasota Limestone from Minnesota. Look closely at some of the stones and you can find tube-like patterns created by invertebrates as they traveled through the mud at the bottom of a deep sea that covered Minnesota around 480 million years ago during the Ordivician period.

Washington isn’t alone in its wealth of architectural fossils. There are fossils in the stones that make up Baltimore and Montreal. The Maine State Capitol has them, too. Every city must have collected fossils in its building blocks. Maybe they’re even in your home. You’ll just have to look.

Photos courtesy of Helen Fields.