Searching for Fossils in the Urban Wilderness

In which the blogger wanders among a city’s buildings, acts weirder than usual, learns when marble is not marble, and avoids museum security – all in pursuit of fossils.


The vistas of the urban landscape offer intriguing contrasts. The typical urban tourist steps back to admire the sweeping lines of that building, shifts her camera to capture this fountain in its entirety, carefully poses the sweating (and complaining) children and spouse in front of that obelisk. These are seekers of the macro vistas.

Lurking on the margins of these scenes is a person on his knees nearsightedly inspecting the stone steps that lead down to the reflecting pool or a person standing outside the museum nearly pressing her nose against the exterior stone wall she is scrutinizing. These are searchers of vistas on a small, very small scale. These are the urban fossil hunters, individuals for whom the quest outweighs any embarrassment stemming from being the odd characters in this environment, the ones who are the objects of furtive glances and puzzled stares and comments. “Now, there’s a weirdo.” “What can he be looking at?” “Perhaps, that just how Americans behave.” “Has to be foreign.” “Hold on tight to your purse.”

Fortunately, for those with paleontological interests, limestone, particularly Salem Limestone, also known as Indiana Limestone, is an integral part of the urban landscape in the United States. As David B. Williams writes in Stories in Stone: Travels Through Urban Geology (2009), “Other stones are older, more beautiful, and have more noble pedigrees, but no other building stone forms as much a part of the collective cultural fabric of the United States as the Salem. No other stone has contributed more to giving our cities and towns a sense of elegance and pride. No other stone deserves to be called America’s building stone.”

The American love affair with limestone has made the urban landscape a fossil hunter’s paradise because this stone, for all of the ease with which it can be worked, the carved detail it can hold, and its overall durability, is, above all, a static, rich stew of fossils. Salem Limestone is a sedimentary rock laid down during the Mississippian Period (some 355 to 320 million years ago) and, given that it is mostly a mixture of fossil shells and pieces of shells, is nearly pure calcium carbonate.

On a humid summer morning, I went in search of fossils in the urban landscape of Washington, D.C. From about a dozen sites that I initially included in my itinerary, I reached only three, thwarted in my grand intent by the typically oppressive Washington heat and, most wonderfully, by my success in finding fossils in those three stone structures. My guide for this foray was Building Stones And Geomorphology Of Washington, D.C.: The Jim O’Connor Memorial Field Trip (link here). This eclectic mix of excerpts from field notes, newspaper articles, guides, and unpublished and undated manuscripts honors the life and work of the late James V. O’Connor, geologist, teacher, and, at one time, the state geologist for Washington, D.C. Among its treasures is a listing of many buildings in the District of Columbia, identifying the stone used in construction, interesting aspects of the construction, and, most importantly for me, where one could proclaim, “Here there be fossils.”

After this hunt, I was helped by the web site that geologist Wayne G. Powell is building to support his course entitled, Earth Sciences in the NYC Urban Environment, which he teaches at Brooklyn College. Particularly welcome is the section of the site that offers superb overviews of various building stones in common use in New York City (link here). At this point, though much of it is under construction, the two sections that could best inform my Washington, D.C. foray are complete – the profiles of Indiana Limestone (used in the Empire State Building and the Flatiron Building in NYC) and Tennessee Marble (used in the JP Morgan Building and the floors of Grand Central Station). Powell walks the reader through the use of the stone for building and its geological history. But, the highlight of these profiles is his treatment of the fossils, if any, that might be found in the stone – I applaud his decision to include several pictures of those fossils since these are invertebrates, and invertebrates are nearly virgin territory for me.

Botanic Garden

The conservatory at the United States Botanic Garden is shown here.

The Botanic Garden is located just southwest of the U.S. Capitol Building, next to the Capitol Reflecting Pool. It is constructed of gray and beige Indiana limestone. Its patio is made of reddish orangey Pennsylvania sandstone. Needless to say, it was the limestone exterior walls that drew me since they held my quarry. The limestone is clearly nearly all fossil.

This first close-up photo of a small section of the wall shows a chaotic mixture of fossil bits. It all looks amazingly porous.



The fossils and the fossil pieces are small. Are these on a micro scale? There is no precise definition of the size threshold for a micro fossil. Some argue that such fossils are those that can only be viewed under a microscope, others suggest that generally fossils of say 1 or 2 mm or smaller qualify (i.e., less than .08 inches). Much of what I found this day probably met that latter threshold. Certainly, nearly all were less than 5 or 6 mm in size (less than about 2.4 inches).

One of my special finds on this hunt was this relatively large brachiopod shell enmeshed in an oblong lens of finer grains of shelly material.  Carbon Freeze in comments about this post on May 30, 2016, and on February 1, 2012 (see below) made the persuasive argument that this shell is a rhynchonellide brachiopod and not a pelecypod, as I had it originally.  Though I wondered whether this was a mold or an actual fossilized shell, Carbon Freeze asserted that it is the latter.  [Later edit:  This paragraph was rewritten on June 2, 2016, long after Carbon Freeze offered the initial correction to the original post.  I apologize to him for being asleep at the switch for so long.]



Though I like this picture for what it shows, my fascination with it comes from the hints of what lies just below the surface. Other shells are just becoming visible. The best are the “open necklaces of beads,” particularly to the right of the brachiopod. I assume these are the edges of shells emerging from the matrix. Lovely.


Capitol Reflecting Pool

The Capitol Reflecting Pool graces the foot of the hill topped by the Capitol. This picture shows the pool and includes the Botanic Garden conservatory in the background.



The pool and its steps are made of Indiana limestone. Tourists circle the pool, comment on the ducks that float on its surface, and dangle hands in the water to gain some relief from the heat. They studiously avoid me as I kneel on the steps and focus my camera on one small spot after another. “Perhaps he’s fixated on chewing gum.”

The limestone steps are awash with the ossicles from crinoids. Ossicles are the round segments that make up the stems or stalks of crinoids, so-called “sea lilies,” which are invertebrate animals, not plants at all. These little disks are typically all that remains.



The fossil tapestry of the steps includes the latticework remnants of the structures built by colonies of bryozoans, tiny invertebrates who lived in chambers within the upright branches. The structures can consist of relatively thick interconnected branches (e.g., Polypora) or fan-like sections (e.g., Fenestrellina). Above and to the left of the ossicle in the middle of the picture above is what appears to be a section of a branching bryozoan fossil. Below it are small segments of fan-like bryozoan fossils.

A better piece of fan-like bryozoan fossil is seen in the picture below, just underneath the spiral shape of what, in my ignorance, I take to be a gastropod fossil (another invertebrate, think snail).
This picture also shows an abundance of crinoid pieces. Unfortunately, I didn’t notice the little brown objects in the upper right hand corner until later when I examined the photo. I have no clue what they might be, extinct or extant.

My favorite picture from the Reflecting Pool shows what I think may be a cross section of a branching bryozoan. Then again, it may be just be one end of a crinoid ossicle. It’s the distinctive color of the fossil that I find most appealing.




National Gallery of Art (West Building)



The West Building of the National Gallery of Art was described by Jim O’Connor as “fossil heaven.” I agree, partly because of the abundance of fossils in its interior walls and floors, and partly because the building is air conditioned. The exterior stone is Tennessee marble.

Of more interest to me is that the interior floors are made of Vermont verde antique marble. According to O’Connor, the men’s and women’s bathroom walls and the panels separating the stalls in the bathrooms are black marble from the Lake Champlain area of New York. (These are the bathrooms located back toward the Constitution Avenue side of the building.)

Both of these interior “marbles” are actually limestone, otherwise there wouldn’t be any fossils to find. To explain this nomenclature confusion, Wayne Powell writes, “Geologists want to understand the Earth, its processes, and its history. Accordingly, geologists classify rocks based upon the processes by which they form: limestone is a sedimentary rock that forms by the precipitation of calcite by chemical or biochemical processes, whereas a marble is a metamorphic rock that forms when a limestone is subjected to high pressure and/or temperature.” (I would add that it’s the pressure and temperature that destroy the fossils in the limestone.) Those individuals building with stone “want to know how a rock will look and behave when incorporated into a building or monument. Accordingly, a quarrier or architect considers a marble to be any relatively soft rock that will take a polish. That includes the rocks that geologists classify as marble, along with compacted limestone, and even serpentinite.”

Let’s first consider the spoils from my search of the floors next to the elevators near the women’s and men’s bathrooms. There are many little and some not so little fossil-generated images frozen in this Vermont marble, but two stand out. And once they're spotted, it is almost impossible to imagine that these particular beauties can go unseen by the several hundred people who walk over them daily.

Outside the elevators by the bathrooms are these two wonderful fossils. One is the heart-shaped cross-section of a clam (a pelecypod, by the way) some 6.7 cm (about 2.6 inches) long. This fossil, embedded in the marble slab, was sliced during the preparation of the stone.



The other appears tantalizingly like the remnant of an Archimedes bryozoan fossil, but as Carbon Freeze pointed in his 2012 comment, it's the wrong time and shape for that.  Which means it's probably the lengthwise slice through some sort of gastropod. This fossil is 9.5 cm (about 3.7 inches) long.



And then there’s the men’s room in the National Gallery of Art. It holds many surprises . . . of the fossil variety. Unfortunately, since I have no expertise using a camera in a dark bathroom, most of the fossil treasures that decorate the walls and panels remain unrecorded. Fortunately, I did capture the outlines in one panel of what might be cross-sections of (I’m guessing here) two Maclurites, (a kind of gastropod), and, despite clicking away with my camera in this restroom, I managed to avoid museum security – not likely to condone picture taking there.





Addendum

In addition to the links given above to material about building stones (and, most importantly for me, their fossils) in Washington, D.C. and New York City, there are other guides to other cities' building stone that are worthy of some paleontological attention. A not very systematic and brief search of the web turned up these, among others.

Montreal, Canada – Building Stones and Fossils of Montreal describes what appears to be a fine walking tour of buildings in Montreal. Lots of fossils. (Link here.)

Baltimore, Maryland – A Geologic Walking Tour of Building Stones of Downtown Baltimore, Maryland from the Maryland Geological Survey is mostly about stones with a passing glance at fossils. (Link here.)

Boston, Massachusetts – David Williams wrote a great piece for the Boston Globe (May 3, 2009), identifying the stone used in various buildings in the Boston area, and giving the geological background on the stone. Fossils make an appearance. The link is to a copy of the article the Globe permitted Williams to post since it’s not on their web site. (Link here.)