By AGNES PASCO CONATY
Credit: Agnes Pasco Conaty
Many structures in the District — the monuments and museums, the federal buildings — reveal much of the underlying geological history of this region. Take the Washington Monument, for instance. The marble exterior faces have a number of characteristics, including shades of color, that indicate the stone was sourced from different quarries, including two right here in Maryland. The core of the structure is bluestone gneiss and granite, also quarried in Maryland, while the interior walls are faced with Maine granite. When finished in 1884, this 554-foot-7-inch monument was the tallest structure in the world. It’s the world’s tallest obelisk and predominantly-stone structure to this day.
Right here in Laurel, we can take a geologic walking tour of historical landmarks, too, that might be seen as monuments, of a sort, to our region’s geology: The Montpelier Mansion and St. Mary of the Mills Catholic Church are two good examples of how geology influenced both architecture and construction in earlier eras. Like most of the city’s historic buildings still standing, the mansion and church were constructed of bricks and clay, which were standard materials in the 18th and 19th centuries.
I’m fascinated by these historic examples of local geology, and my fascination prompted me to learn more about the ground my home in West Laurel stands on. What lies beneath its foundation — and even beneath my own feet? To answer these questions, I turned to easy-to-access, reliable sources including the U.S. Geological Survey (pubs.usgs.gov) and the Maryland Geological Survey (mgs.md.gov).
The state’s site has a map showing six distinct but connected landforms, five of which, stretching from the state’s western border east to the Chesapeake Bay and Atlantic, we can explore on foot. (The sixth is the Atlantic Continental Shelf, which is offshore.) Laurel, along with the greater D.C. region, is located along the north-south border between the Piedmont and the Atlantic Coastal Plain, the landform that gives way to the continental shelf.
Rocks found in Maryland’s Piedmont, to our west, are primarily igneous and metamorphic; igneous rocks form from volcanic activity and, with sufficient pressure over time, transform into metamorphic rocks.
The Atlantic Coastal Plain, spreading out to out to the east, has primarily sedimentary rocks (i.e., sandstone, limestone and shale). Sedimentary rocks form when small rock fragments, typically resulting from weathering or erosion, are compressed over thousands of years. Many sedimentary rocks in our area, for instance, have formed from deposits of the Patuxent and Patapsco rivers.
Dinosaur Park, a 22-acre tract under the auspices of the Prince George’s County Department of Parks and Recreation, offers us an unusual geological glimpse into our region’s history. In 1858, African American workers mining iron ore at the site discovered dinosaur fossils, the first ever found in Maryland.
Since those first finds, scientists have discovered hundreds of dinosaur teeth and bones at the site; most are from sauropods (long-necked herbivores), and theropods, which, like the Tyrannosaurus rex, were large predatory carnivores. The majority of these fossils date to the Cretaceous period, which followed the Jurassic period, taking place 145 million to 66 million years ago.
Dinosaurs roamed most of the Mid-Atlantic region during a period that lasted roughly 158 million years.I work at NASA/Goddard Space Flight Center, and we have an exhibit of dinosaur artifacts, most of which were found right here in Greenbelt by Ray Stanford, an amateur paleontologist with an extraordinary knack for finding dinosaur tracks.
During excavation of a Goddard parking lot in 2012, Stanford unearthed the footprint of a nodosaur, a heavily armored plant-eating dinosaur from the late Jurassic period, some 145 million years ago. (You can read Stanford’s account of his finds in this article in Nature magazine: tinyurl.com/yuw8p56t). Subsequent excavations at Goddard have uncovered sauropod tracks like those found at Dinosaur Park, as well, and scientists excavating the parking lot also found pterosaur tracks. Not the ancestor of a bird or bat, and not a dinosaur (though on a branch of the same family tree), the pterosaur was the earliest-known vertebrate capable of flight.
My office at Goddard is a few yards from this intriguing exhibit of digs, and sometimes I spend my lunch break looking at a cast of a fossilized dinosaur poo.
If you’re eager to learn about rockhounding, there are clubs you can join to connect with others who share your interests. I can recommend three clubs right here in Maryland: the Maryland Geological Society (mdgeosociety.org/), the Baltimore Mineral Society (tinyurl.com/2hpe3z3h) and the Southern Maryland Rock and Mineral Club (smrmc.org/).
A quick search online will turn up numerous guides to common rocks and minerals, including specimens you may easily find in our area. Rockchasing.com has a particularly good section about Maryland’s rocks and minerals that includes a list of sites where you can find each type. Rockchasing’s Maryland resources are at tinyurl.com/yfrw7d2b.
One of the very best ways to experience rockhounding is to start in your own backyard (like I did) — you may be surprised what you can find right under your feet! If you live near a creek (like I do), you may find rocks and minerals, maybe even shells, that have been polished as they’ve been tumbled, over time, by moving water.
I encourage you to get a nice journal so you can describe your digs and draw them in detail. If you catch the rockhounding bug, consider investing in a hand lens and a rock pickaxe, too. It’s never too late to follow your curiosity and dig right in.
