On the Rocks

On the Rocks

A morning rain has cleared, and the trail up West Rock is slick as I follow Yale geologist David Evans to the top. We’re in search of evidence of the glaciers that scraped through here sometime in the last two to three million years. Evans has already given me a volcanic tour of East Rock, but after what he calls “an intermission that’s 200 million years long,” during which not much of geological note happened, there’s a dramatic second act to be viewed, and West Rock is the place.

The trigger for that glacial second act, Evans explains, was the rise from the ocean of the Isthmus of Panama, which “shut off the current that had been flowing from the Atlantic into the Pacific.” This deflected the Gulf Stream and transported warm water northward, where it met polar air, creating snow and, eventually, ice caps. Though we often refer to “the Ice Age,” Evans says there were more like 50 ice ages in this period when glaciers advanced and retreated across North America.

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The entire Connecticut landscape was under ice 20,000 years ago, much of it as thick as New York City’s skyscrapers are tall, Evans says. Long Island is the “pile of debris” that was left behind when the last ice retreated. What we’re walking on as we climb West Rock Ridge’s red trail from Springside Avenue is the stone and bedrock from which some of that Long Island debris was scraped.

Evans stops to point out a bare patch of sandstone bedrock in the middle of the trail. There isn’t much of it left up here. That’s because the sandstone is made of rounded grains, loosely held together, whereas the trap rock that remains “has three-dimensional, jigsaw-like interlocking” grains less likely to be broken apart. Farther up, near the cliff’s edge, Evans points out another small knob of sandstone. He knows there are several more scattered around the area, and he leans precariously over the cliff’s edge to scout for them.

West Rock’s cliff face is built of the same columned trap rock we examined on our earlier East Rock visit: magma that cooled underground and later rose to the earth’s surface. As I learned then, these two aren’t two separate ridges; they’re both made of the same basaltic rock and connected by a similar beam that’s now only partially above ground.

But West Rock happens to be the better place to look for the glaciers’ calling cards. Just off the trail, for example, we find an outcrop of stone that was polished smooth by passing glacial ice. This morning it’s glistening wet from the rain. We scramble over it, avoiding slippery lichen, and reach a small natural amphitheater just up the trail. It’s covered with spray painted graffiti, but Evans, with his geologist’s view, notes that “our little, futile attempts at expressing ourselves are no match for the long-term record of what actually happened here.”

What actually happened is glaciers left their marks as well, in the form of parallel scratches pointing southwest that were carved by debris at the bottom of those deep and mighty sheets of moving ice. “They look like they’re shooting up over the edge of the cliff, so the ice was temporarily going uphill,” Evans notes, adding that the ridge was “not very much of a barrier” to such a deep and heavy glacial flow. A cloudy day like this one is best for seeing the scratches, he adds, because sunlight accentuates other cracks and crevices that have nothing to do with the glaciers.

When we reach the overlook at the top, we pause to admire the view back across the city toward East Rock’s own ruddy cliff face. Then we set off down the park road to Judges’ Cave (though, for a more leisurely stroll, the blue trail is the way to go). The leaning boulders that make the cave in which Judges Whalley and Goffe hid from the wrath of King Charles II are actually one big glacial “erratic” that has broken into many pieces due to “frost wedging, roots or whatever was getting in there,” Evans says. Walk around the sides and back, and you can see how all the pieces once might have fit together. Boulders like these are evidence of where one of the glaciers retreated. “It got to the top, and then coincidentally, that was also the time when the ice margin was retreating and sort of left there by accident,” Evans explains.

Nearby, another flat, smooth rock surface is the site of more glacial scraping, this time overlaid not with spray paint but with 19th-century graffiti. We crouch to decipher some of the names, dates and images carved into the stone, like “Geo. E. Blakeslee, S.D. Hyde, 1874.” The carvings aren’t easy to read. But coursing beneath them, from lower right to upper left, the now familiar diagonal scratches of that ancient glacier are still visible—at least, in geological time, for a little while longer.

West Rock Ridge State Park
Entrance off Wintergreen Ave between Level St and Tierney Rd, New Haven (map)

Written and photographed by Kathy Leonard Czepiel. This story originally published on October 25, 2018.

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