Francis J. Degnan
The reasons that the Puritans chose to move to this state are directly to our geological past. The formation of our rich central valley and our sheltered coastline has taken millions of years. It wasn’t until the sixties when the theories of plate tectonics and the resulting continental drift were verified and accepted that a true picture was developed explaining Connecticut’s unique landforms. Geologists divide Connecticut into four major regions using the “terrane concept. Terrannes lump together rocks with similar or related histories, even though these rocks may have quite dissimilar looks or compositions”(Bell 140). The four terranes of Connecticut are, 1) the Western New England Upland, 2) the Connecticut Valley Lowland, 3) the Eastern New England Upland and 4) the Coastal Lowlands(Bell 10). Connecticut is the third smallest state, only about ninety miles east-west and seventy-five miles north-south comprising 5,018 square miles(World Book Ci-Cz 763). Despite the size, within the major regions we find parts of other continents, the remains of ocean floors and the reminders that dinosaurs once walked in our Connecticut River Valley. When a geologist tries to put the time that has passed into perspective he thinks in terms of millions of years, but there are some four billion years to be accounted for. Divisions of this enormous time period were made that were primarily determined by rock’s fossil remains. “The Geological eras are called Cenozoic-recent life. Mesozoic-middle life, Paleozoic-old life, and Cryptozoic-hidden life”(Rodgers 3). It was during the Paleozoic era that the first of a series of collisions started that heralded the formation of Connecticut’s ancestral bedrock.
“Eighteen miles of solid crust sits on 3,800 miles of unstable mantle and core. If the earth were scaled down to the size of an egg, the shell would be more than twice the thickness of the crust”(Little 11). Areas of thicker crust, called plates float on top of the mantle moving ever so slowly because of the convection currents from below. These plates may collide creating mountain ranges. Our West Coast is an example of such an on going collision, that is complete with earthquakes along the ‘fault’ or collision boundaries with the accompanying volcanic action of Mount Saint Helens. Such an area is called a subduction zone. Connecticut has been the site of three such continental collisions. The first of these occurred some 500 million years ago during the Paleozoic Era. As a small area called the Bronson Hill Plate slowly approached the Laurentia Plate, essentially the land mass that we call North America. A body of water named the Proto-Atlantic and its muddy sediment grew more shallow and developed large coral banks in a tropical climate as it was compacted between the two plates. Eventually this area was to make up the Westem Highlands of Connecticut. The middle of this one hundred fifty million year period the earth’s most spectacular collisions happened and a super continent was formed called, ‘Pangea’ a Greek word meaning ‘all lands’. As a direct consequence of this uniting of the plates the rest of Connecticut’s highlands were formed. What took place was another collision first with series of mini-continents, called ‘Avalonia’, which may have been between five hundred and three thousand miles from our shores in the middle of a body of water called the Iapetos Ocean. In mythology Iapetos was the father of Atlas. The second collision was with the African Continental plate that was equally distant from the mini-continents. These land masses all compacted and crunched. Imagine the pressures exerted when these land masses collided! The heat and pressure of compression changed the coral sea bed into limestone and marble, clays turned into slate, sandstone into quartzite and large areas of ocean floor to gneiss and schist. Along route 8 in Higganum Connecticut you can see folds in the metamorphic rock, the rock resembles a marble cake. Today if we consider the areas that are currently undergoing continental collisions we find mountain ranges, the Rockies and Himalayan chain, earthquake zones and volcanoes. What happened to Connecticut? “At one time, the rocks at today’s surface were more than five miles underground: the persistent nibbling of the land by erosion has removed at least that much . . . Yet the outlines of today’s terranes probably bear close resemblance to those of earlier times”(Bell 151).
Now as we are aware the drift didn’t come to an end, we are no longer one enormous land mass. The megacontinent didn’t have a stable foundation and forces from within the mantle and core pulled at the largest plates once more. The formation of our Connecticut River Valley began as the retreating African Continental Plate tried to separate along the same boundaries that had existed before the collision. The strain on the crust along this area caused lava flows above the ground. Above ground flows are called extrusive. Flows that were trapped below ground are called intrusive. The extrusive lava was covered by sedimentary run off from the surrounding mountains. Today we call these lava flows traprock. At 190 million years old it is Connecticut’s youngest rock. As the pressure of the drifting continent increased a major crack occurred. This rift is called the Eastern Border Fault. The Eastern Highland landmass slid away from the Western. It didn’t crack and open up a gaping hole, it slid down and to the East on a steep diagonal. The lava and sediments that had layered horizontally on the surface were now pitched down to the east exposing their western most edges that now became exposed. This rift created Connecticut’s central valley. This rift extends into Massachusetts not quite to the Vermont and New Hampshire border. Throughout this valley are the basalt ridges, the most noted of which is the Metacomet ridge. When a map of the terranes of Connecticut is viewed, the funnel the point, of which is located in the New Haven area. Why then is it that the Connecticut River’s estuary at Saybrook? The Metacomet ridge is the problem, it forced the river to cut a path through Eastern Uplands near Meridan to reach Long Island Sound. This ridge formed a topographical boundary isolating New Haven and Hartford. It is interesting to note that the desire to be involved with river trade encouraged the New Haven area businessmen to construct the Farmington Canal after reports of the success of the Erie canal were publicized. The canal ran just west of the Metacomet ridge and it was hoped that it would provide a more attractive path to the Sound. It opened in 1827 only to be replaced in a few short years by the railroad that truly broke the traprock barrier.
New Haven finds itself located in a unique position. The Eastern Border fault converges with the Western Uplands at our harbor entrance. If we stand at Lighthouse Point and look to the west we are looking at Iapetos oceanic terrane that is from the middle to early Paleozoic age about 350-500 years old metamorphic rock. Looking to New Haven we see the red-orange of East rock the Early Jurassic Age igneous rock only about 190 million years old. At our feet and along the coast we are on Avalonian continental terranne that is from the Protozoic age some 600-700 million years old metamorphosed sedimentary and igneous rock. Just out of sight to the north and east is more 350500 million year old Iapetos oceanic terrane.
The last of Connecticut terranes of be discussed is the Coastal. The indented natural seacoast that has many natural harbors is one of Connecticut’s greatest resources. Bell points out that the thirty harbors of differing sizes along our coast have, “supported such enterprises as fishing, lobstering, oystering, whaling, shipbuilding, international trade, ferrying, privateering and pirating. . .Today we can add marinas, vacationing, tourism, year-round residences submarine building and a navel base to the list”(78). It is amazing that there is six hundred eighteen miles of coastline within the ninety miles from the New York to Rhode Island State lines. These were relatively safe harbors because of the absence of the ocean’s pounding erosive force. Long Island is a natural boundary protecting our shoreline from all but the worst storms. This sheltering effect is a result of our most recent major geological phenomena, glaciation. As the crustal plates have shifted over the millions of years our area has changed from a tropical to a more temperate climate. The red soils and limestone deposits found in our state are indicative of a much warmer period. Our shifting on the globe to a more northerly position allowed for, “over 20 glacial advances during the last 2 1/3 million years.” At times our area may have been under as much as a mile of ice. In fact today some scientists say we are between ice ages. “Even Mt. Washington’s 6,300-foot summit is capped by erratic boulders, mementos of victorious ice . . . “(Little 55) Initially the glacier grew and was very active, eroding fertile soil and rock from the inland areas. The force was so great that gouges in bedrock are visible today on the uphill ridges the glaciers ground over. From the downhill side boulders were plucked because of the pressures exerted by the glaciers. The New England area found itself under a huge immobile glacier. New England’s hilly terrain slowed the glacier down. As the climate warmed again the glacier melted. It was an uneven melting, no doubt darker, dirtier areas absorbed more heat causing holes in the glacier. Geologists have given the different types of glacial formations and deposits names. We have kettles, drumlins, eskers, till and moraines. Long Island is essentially a type of glacial deposit called a moraine. The rate at which the ice melted and the speed at which the glacier was moving were nearly equal. This resulted in the massive amounts of soil and rock that had become part of the glacier as it moved being dumped in a long narrow pile. Block Island, Martha’s Vineyard and Nantucket also are moraines. Not only did the glaciers protect our coast from erosion by building Long Island it also scraped and notched it.
In the Connecticut River Valley the glacier caused, “New England’s largest glacial lake, Lake Hitchcock, which eventually extended along the Connecticut River Valley for 150 miles to Lyme, New Hampshire”(61) It is estimated that the lake was formed about 13,700 years ago a combination of glacial ice and deposits blocked the spillway. Just imagine as the glacier cliff melted, icebergs thundering into the lake. At the same time many streams annual brought large amounts of sediments into the lake. The large aggregate formed deltas of gravel that are used today in construction. The further from the origin of the delta the finer the deposits, gravel first, then sand and finally clay. The yearly snowmelt run off in the spring carrying coarse sediment and the slower more constant flow of the rest of the seasons carrying finer sediment caused pairs of clay and sand or silt deposits called varves. Along many of Connecticut’s rivers clay pits that were used to make brick still can be found. The Rocky Hill dam was able to withstand, “the forces of erosion for several thousand years”(63) All at once the lake was gone and a vast barren lake floor remained. Winds swept the lake floor, clouds of dust and sand piled up in certain locations along the eastern edge of the valley creating, “‘ the most extensive inland dunes in New England. “‘(70) Streams cut new channels to the river through the different types of sediments. The next several thousand years brought more rich sediment to the Hartford floodplain. This was the land Thomas Hooker sought for settlement.
