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Rocks in my head: A top geologist sets me straight

Granite is the most common rock in Connecticut, right? 

In addition, glaciers carved the state’s hills and valleys about 12,000 years ago.

Also, any large, isolated boulder is called an erratic.

Wrong, wrong and wrong.

Former state geologist Ralph Lewis cleared up a few misconceptions about rocks the other day while hiking with our small group through the 201-acre Candlewood Hill Wildlife Management Area in Groton.

This stunning preserve, replete with ravines, boulders and overhanging ledges, is an ideal setting to observe how tectonic forces shaped Connecticut’s bedrock hills and valleys.

Purchased by the state in 2017 despite objections by local officials who hoped it would be developed to generate tax revenues, the preserve had been owned by Tilcon, an asphalt and concrete paving materials company with divisions throughout the Northeast.

The Groton Open Space Association and other conservation advocates persuaded Connecticut to protect the property, bounded by the Gold Star Highway, Interstate 95 and Rogers Road, because it connected with other parks and preserves to form an “emerald necklace” of unspoiled land. The new preserve contains lush stands of mountain laurel, vernal pools, sphagnum bogs, and most notably, one of the state’s largest pitch pine forests, measuring more than 40 acres.

Colonists referred to pitch pine as candlewood due to the tree’s high resin concentration. Seventeenth-century settlers also extracted turpentine from pitch pine and burned knots as candles.

Before the five of us began our hike, Lewis set up a trailhead “classroom” in the bed of his pickup truck, complete with rock samples, maps, charts and diagrams, and presented a 30-minute lecture describing current geologic thinking regarding the region’s tectonic and glacial history. He told us:

— Most people mistakenly refer to the rock commonly found in Connecticut’s mineral layers as granite, but most of that rock typically is gneiss — granite that has been heated under pressure hundreds of millions of years ago so that the minerals recrystalized into distinctive layers. Gneiss therefore is granite that has been metamorphosed and foliated to resemble pages viewed from the side of a book. While granite is prevalent in Rhode Island, the Candlewood Hill Wildlife Management Area is one of the very few places in southeastern Connecticut where it can be found. The property includes remnants of old granite quarries.

— Connecticut’s hills and valleys were not carved by glaciers, but by 200 million years of weathering and erosion that removed eight miles of bedrock following the formation of the Appalachian Mountains. The wearing down of softer rocks created valleys; harder rocks remained as hills. Four separate periods of glaciation later smoothed these hills and valleys. The last ice sheet in the region melted in the vicinity of what now is Ledyard about 22,000 ago. Over the next 4,000 years, virtually all ice had melted out of Connecticut.

— Many people, myself included, often have erroneously referred to any boulder that lies isolated in the woods as a glacial erratic, but that term only applies to a rock that rests on another rock of a different composition. Thus, a basalt boulder resting on basalt is a glacial boulder; if that same basalt boulder rested on sandstone it would be termed an erratic. What’s more, erratics don’t have to be big boulders; they can be as small as pebbles.

I had invited Lewis to join last week’s hike after he emailed me to “offer some gentle, and hopefully helpful, guidance as to timing of the last glacial melt back and use of the term erratic.”

Lewis, who served as state geologist from 1997 to 2003, now is chair of the Connecticut Academy of Science and Engineering’s Environment Committee, is a member of the National Academies, National Research Council, Ocean Studies Board, and is a professor in residence at the University of Connecticut’s Marine Sciences Department at Avery Point in Groton. A Hadlyme resident, he also is a past president of the Lyme Land Conservation Trust.

During last week’s hike, Lewis’s geologic observations were interspersed with biologic/botanical commentary from Maggie Jones, director emeritus of the Denison Pequotsepos Nature Center in Mystic. Over the past couple months, she has identified countless birds, wildflowers, trees and other flora and fauna, reminding us how fortunate we are in southeastern Connecticut to have access to so many wonderfully varied open spaces.

Lewis agreed, and noted the preserve also has an abundance of “leaverite” rocks.

“Leaverite?” I asked.

“Leaverite,” Lewis replied, with the tiniest hint of a smile. “As in ‘Leaverite there.’”

There are two entrances to the Candlewood Hill Wildlife Management Area, leading to some five miles of trails. One access is just north of the landfill on Flanders Road; another is off Route 184 just west of Rogers Road. Additional information is available on the Groton Open Space Association website,

During last week’s hike of a couple hours, we did not see another person. Our group has been exploring less-traveled parks and preserves in recent months while maintaining coronavirus social distancing.

If you have a favorite hiking or paddling destination, leave an online comment on this column, or send an email to

Stay safe, everyone, keep active, and please remember to hike and paddle responsibly.


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