The Traprock Landscapes of New England. Peter M. LeTourneau

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      The Hanging Hills, including, from right rear to middle foreground, East Peak, Merimere Notch, South Mountain, Cathole Notch, and Cathole Peak, are the most rugged and picturesque traprock landforms in the Connecticut Valley. Termed cuestas by physical geographers, the characteristic “tilted” landforms were created by eons of earth movement and erosion. View from Chaucey Peak.

      Rising abruptly in amphitheater-like ranks of rugged talus slopes and sheer cliffs, the traprock hills of the Connecticut Valley have a greater topographic prominence than many of the taller but more rounded mountains in New England. Thus, these “mountainous hills” project a more dramatic alpine aspect than anticipated from their relatively moderate elevations. For example, the southern cliffs of East Rock and West Rock near New Haven reach elevations of only about 350 feet and 400 feet, respectively, but because they rise in sheer cliffs from the tidal creeks at their base, they tower over the city, and once served as important landmarks for ships navigating Long Island Sound. A great east-west-oriented inlier of the Western Range, the Sleeping Giant massif (el. 708 ft.) in Hamden commands the Quinnipiac River lowlands as the largest isolated traprock landform in the Connecticut Valley. Noteworthy as the highest summits near the Atlantic coast south of Maine, West Peak (el. 1,024 ft.) and East Peak (el. 978 ft.) of Meriden’s Hanging Hills similarly dominate the topography of the central Connecticut Valley. Mount Tom (el. 1,202 ft.), the tallest traprock summit in the Connecticut Valley, towers more than 1,000 feet above the Manhan River valley near Easthampton, Massachusetts. Nearby, the western cliffs and ledges of Mount Holyoke drop more than 800 feet to the extensive agricultural fields on the Connecticut River floodplain.

      Because of the sheer number of traprock peaks, crags, cliffs, and ridges making up the volcanic landforms of the Connecticut Valley, and a long history of human occupation, a large number of formal and informal names have been attached to the hills. Many of the designations have changed since colonial times, and the geographic names also vary with the local frame of reference; thus, East Mountain may well be West Mountain, depending on one’s point of view. The nomenclature of the traprock hills is based on the following: geography (East Rock, West Rock, West Peak, East Mountain, South Mountain); topography and appearance (Ragged Mountain, Peak Mountain, Pinnacle Rock, Short Mountain, High Rock, Tri-Mountain, Bluff Head, Sugarloaf, the Hedgehog); nearby towns (Farmington Mountain, Meriden Mountain, Avon Mountain, West Suffield Mountain); wildlife (Rattlesnake Mountain, Rabbit Rock, Cathole Peak, Goat Peak); historic associations (Mount Tom, Mount Holyoke, Chauncey Peak, Mount Higby, Peter’s Rock, Hachett’s Hill); the first inhabitants (Totoket, Pistapaug, Manitook, Nonotuck, Norwottock); colors (Black Rock, Red Rock, Blue Hills); and tales and legends (Mount Lamentation, King Philip Mountain).

      Rising to an impressive elevation of 1,024 feet, West Peak (background) is the highest traprock summit in the Connecticut Valley south of Mount Tom in Massachusetts, and the tallest peak located within twenty-five miles of the Atlantic coast south of Maine. View from Ragged Mountain.

      Illuminated by evening alpenglow, Ragged Mountain’s sheer cliffs project an alpine majesty lacking in many of the taller, but more rounded, mountains of New England.

      In the legends of the Quinnipiac River tribes, Sleeping Giant (Mount Carmel) ridge was the reclining form of the giant, Hobbomock, put to sleep for all time for his mischievous deeds. Today, the diabase ridge is part of popular Sleeping Giant State Park, where dozens of hiking trails, a stone lookout tower, and picnic facilities await outdoor enthusiasts.

      The “blue hills” of the Western Range stand high above the misty Quinnipiac River lowland. From north to south along the horizon (right to left), Peck Mountain, Mount Sanford, High Rock, and the north end of West Rock Ridge form a line of lesser-known traprock peaks on the southwestern edge of the Connecticut Valley.

      The two main trends of traprock hills in the Connecticut Valley result from slight differences in their geology. The Metacomet Mountains, from Saltonstall Ridge to Mount Holyoke, are made up of basalt, which is finegrained lava that cooled quickly at or near the surface. The Western Range, from East Rock to Manitook Mountain, formed from basaltic magma that cooled slowly beneath the surface in dikes and sills, creating a coarse-grained igneous rock called diabase.

      The traprock hills follow two major trends through the Connecticut Valley. The main range forms a great “wall” of crags from Mount Holyoke in the north to Saltonstall Ridge near Long Island Sound. Benjamin Silliman described the particular linear arrangement of this range in 1820: “In many parts of this district, the country seems divided by stupendous walls, and the eye ranges along, league after league, without perceiving an avenue, or a place of egress.” This main range of lava flows are herein designated the Metacomet Mountains, to distinguish their particular topographic aspect, and to streamline the cumbersome geographic nomenclature of the Connecticut Valley (please refer to Note on Terminology and Usage).

      The volcanic veins and dikes that follow the western side of the valley as a series of discontinuous ridges and hills were named the Western Range by the noted geographer William Morris Davis in 1898. The Western Range runs from West Rock near New Haven to Manitook Mountain in Suffield, Connecticut, near the Massachusetts border. The specific rock type (diabase, see below) and characteristic “massif” landforms distinguish the Western Range from the typical cuesta ridges of the Metacomet Mountains. Known mainly to local hikers, the remote summits of the Western Range are among the least disturbed areas in the Connecticut Valley. The hills of the Western Range also have the most colorful names of any of the Connecticut Valley traprock crags, including Sleeping Giant, Onion Mountain, the Hedgehog, and the Barndoor Hills. Among the most scenic landforms in the region, East Barndoor Hill (el. 580 ft.) and West Barndoor Hill (el. 640 ft.) in West Granby, Connecticut, form a particularly interesting pair of steep traprock promontories separated by an unusually deep and shady notch.

      Moonrise over the cliffs of South Mountain. Basalt is the most abundant crustal rock type on both the earth and the moon. The lunar “seas” were formed from enormous outpourings of basalt lava roughly 3 billion years ago. Radiometric ages determined from the samples of the CAMP basalts indicate that the lava flows of the Connecticut Valley are approximately 201 million years old.

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      Born of Fire

      TRAPROCK GEOLOGY

      Eruptions … took place from great fissures … of the earth’s crust. The lava which then came up and filled the fissures, and in many places outflowed, is the rock we now call trap.

      James D. Dana, On the Four Rocks of the New Haven Region (1898)

      The story of the Connecticut Valley begins in the early Mesozoic era (the age of dinosaurs), a time when the continents were joined in a single large landmass, or supercontinent, called Pangaea (“all land”). During the Late Triassic period, beginning about 220 million years ago, global tectonic forces caused the crust of Pangaea to thin and separate, a precursor to the eventual formation of the early Atlantic Ocean in the Middle Jurassic, around 160 million years ago.

      The thinning and СКАЧАТЬ