The Geology of Connecticut

Excerpted from Great Day Trips to Discover the Geology of Connecticut, by Greg McHone, Ph.D.

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Geologists look at rocks as if each one has its own story to tell. They hope that put together their stories will complete a history of the earth and help us understand how it was that the world came to be as we see it today.

Of course, some stories are more interesting than others—and few can rival Connecticut rocks for the stories they have to tell.

It takes just a short drive in any direction to see that the geologic history of Connecticut is long and full of twists. Along nearly every highway are outcrops or road cuts that reveal distinct and different rocks of all kinds. Unique varieties are found in practically every part of the state—and each makes its own contribution to the knowledge of the state's geology.

The Connecticut story

Look at Connecticut rocks together and you have a geological story with the ingredients of a true epic. In their forms, shapes and colors is evidence of colossal forces, locked for billions of years in a global tug-of-war, which has made and remade the face of the Earth over the vast expanses of deep time.

The oldest reveal continental collisions so collossal they raised mountains thousands of feet high. Others testify to the slow, yet relentless effects of weather and the elements that later all but carried these peaks away. Great columns of stone mark times when the earth's crust cracked and split until floods of lava poured out over thousands of square miles. Sandy beaches and boulder fields along the southeast coast are leftovers of a time in the more recent past when Connecticut was frozen beneath immense sheets of ice.

Discovering geology

Connecticut's diverse geology, combined with the state's small size, makes it an extraordinary natural laboratory. You might drive for days in other states and not see as great a variety of geologic features as can be discovered in Connecticut in an afternoon.

From Salisbury to Stonington, it's easy to travel over billion years and to explore some of the most significant events in Earth history.

There are many fine examples of metamorphic rock in the northwest hills, formed under immense pressures during continental collisions. Among them is the Stockbridge marble, rocks formed from the seafloor at the bottom of an ancient former ocean.

Sedimentary rocks, cemented together from sand and mud, define the Connecticut Valley. Their layers kept a record the past that reveals details of the climate, plants and animals of two hundred million years ago.

Igneous rocks, formed from molten volcanic rock that later cooled and hardened, are also common. Igneous rocks form the great ridges that form the backbone of the state and today offer some of the most spectacular local hikes. Still others formed deep beneath the earth's surface and are seen today as the massive granites along the southeast coast.

Next / Third / Last

Connecticut is made up of several different bands of bedrock, each with their own unique geologic histories. In barely 5,000 square miles, you can find rocks that are as much as a billion years old, others that are half a billion years old, and still others that are 200 million years old. The "Great Unconformity" (above) is a place where relatively younger layers of sedimentary rocks lay atop older metamorphic bedrock. Photo by Greg McHone.

Great Day Trips to Discover the Geology of Connecticut, by geologist Greg McHone, gives a complete geologic history of Connecticut, and describes field trips to some of the state's most fascinating geology sites—all within a short drive or right down the road.

Columns of rock known as basalt are the remains of times when lava flowed in the central Connecticut lowlands. Photo by Greg McHone.