Hard Knocks, Hard Rocks: Geology of the Holyoke Range

By Elizabeth Farnsworth Gazette Contributing Writer

The Pioneer Valley is an exhilarating place to be these days, rich in restaurants, eclectic music, boutiques and art museums. But if you think the Five College corridor is a happening place now, you obviously weren’t around during some of its most thrilling times— about 200 million years ago. Really, there was never a dull moment back then, when volcanoes and lava flows were reshaping the earth that now lies under our feet.

Why do we care about that bygone era? Because the geological forces active then largely created the signature landmark of our region: the Metacomet Range. From Poet’s Seat in Greenfield, south through the Holyoke and Mount Tom ranges all the way to West Rock in New Haven, Conn., the Metacomets form the enduring backbone of west-central New England.

The drama began about 260 million years ago, when our region was part of a larger continent called Pangea, a mash-up of the North American, African and Eurasian continental plates. These were cozy times, when all the land masses on earth seemed to want to cuddle up together near the equator. But alas, the tight relationship could not hold up against the relentless strain of plate tectonics. The Atlantic Ocean began to widen, creating great fractures and rift valleys in the torn land. Like all break-ups, this one was accompanied by pyrotechnics and upheavals, with North America eventually getting custody of parts of Africa and Eurasia (including the granites of Worcester and eastern Massachusetts) in the messy aftermath.

During this comparatively brief period (geologically speaking) of half a million or so years, fissures erupted, spewing vast amounts of flowing lava. Anyone who has seen the hyperactive Mount Kilauea in Hawaii or created a baking-soda-and-vinegar volcano in the kitchen for a science project can visualize the scene.

Lava welled up through vents and dribbled out of small cinder cones, covering the landscape in a layer of molten rock hundreds of feet thick. Once hardened, this lava formed basalt—a hard rock composed of fancy-sounding minerals like pyroxene and feldspar. (The latter yields some calcium when it weathers, an important nutrient that is exploited by a rich diversity of present-day plants on the Metacomet Range.) Basalt, cracking under pressure, broke into angular columns, creating the striking vertical pillars we see in outcrops at Titan’s Piazza and the summit of Mount Tom. These columns are called “trap rock” from the Swedish word for “stairs.”

As it still does today, water worked its way through these cracks, breaking the basalt down into blocks. Tumbling blocks settled at the base of the slopes, creating jumbled masses of “talus” (Latin for parts of the foot). Today, the treacherously slippery scree (rock fragment) slopes forming a skirt around the base of the Metacomets trap cool air long into the summer and support plant species accustomed to more northerly climes. Water further eroded the basalt into sediments, washing them into streams and lake basins. These fans of iron-rich sands and gravels make up the vivid red arkose sandstones we see exposed on the flank of Mount Sugarloaf as we drive across the Connecticut River on the Sunderland Bridge on Route 116. Atop these lie more layers of basalt, and still more layers of younger sandstone—a Dagwood sandwich of rock testifying to at least four episodes of violent eruption, followed by erosion.

 

While fire and water were doing their thing during this tumultuous time, dinosaurs traipsed into and through the valley, munching on the rich vegetation of the subtropical swamps or on each other. Lest you think I’ve been telling tall tales about this vulcan planet, you can see for yourself the evidence the dinos left behind. Tracks of whole families of dinosaurs boogie their way across sandstone exposures at Dinosaur Footprints off Route 5 in Holyoke; most are of Eubrontes, a 20-foot-long granddaddy of Tyrannosaurus rex. Here and farther south at Dinosaur State Park in aptly-named Rocky Hill, Conn., other species of these out-sized reptiles (and fish and ferns and much more) can be seen.

Edward Hitchcock, former president of Amherst College, puzzled over these footprints in the 1830s, recognizing their antiquity and thinking perhaps they were made by ancient gigantic birds. (His theory turns out to be somewhat prophetic: today, birds are known to be living descendants of dinosaurs—think about that the next time a goldfinch-o-saurus visits your feeder!).

The discovery of long-extinct giant creatures overturned our earlier notions of a static, placid earth. Things weren’t always as peaceful in the Happy Valley as they are now, but they sure were exciting.

Resources

For more information, read Richard D. Little’s delightful book, Dinosaurs, Dunes, and Drifting Continents: the Geology of the Connecticut River Valley (3rd Edition). 2003. Earth View, LLC.

For directions and other information about the Dinosaur Footprints in Holyoke, visit http://www.thetrustees.org/places-to-visit/pioneer-valley/dinosaur-footprints.html.

To learn more about Dinosaur State Park in Rocky Hill, Conn., visit http://www.dinosaurstatepark.org. 

Amherst College’s Museum of Natural History houses the world’s largest collection of dinosaur tracks, which was begun by Prof. Hitchcock, and a large vertebrate paleontology collection. More information at https://www.amherst.edu/museums/naturalhistory/collections/paleo_vert.

Elizabeth Farnsworth is Senior Research Ecologist at the New England Wild Flower Society, and a teacher and scientific illustrator. Her favorite movie is Jurassic Park.

Earth Matters, written by staff and associates of the Hitchcock Center for the Environment at 525 South Pleasant St., Amherst, appears every other week. For more information, call 413-256-6006, or write to us.

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