page_title: Metacomet Ridge
section_title: Geology
hierarchical_section_title: Metacomet Ridge / Geology
caption_attribution_description: English: Farmington traprock quarry near Plainville, Connecticut. The quarry is mainly within basalt (‘traprock’) of the Talcott Formation of the Hartford Basin. This basalt is underlain by red siliciclastics of the Shuttle Meadow Formation. Both formations are lowest Jurassic in age and belong to the Newark Supergroup.
context_page_description: The Metacomet Ridge, Metacomet Ridge Mountains, or Metacomet Range of southern New England is a narrow and steep fault-block mountain ridge known for its extensive cliff faces, scenic vistas, microclimate ecosystems, and rare or endangered plants. The ridge is an important recreation resource located within 10 miles of more than 1.5 million people, offering four long-distance hiking trails and over a dozen parks and recreation areas, including several historic sites. It has been the focus of ongoing conservation efforts because of its natural, historic, and recreational value, involving municipal, state, and national agencies and nearly two dozen non-profit organizations.
  The Metacomet Ridge extends from Branford, Connecticut on Long Island Sound, through the Connecticut River Valley region of Massachusetts, to northern Franklin County, Massachusetts, 2 miles short of the Vermont and New Hampshire borders for a distance of 100 miles. It is geologically distinct from the nearby Appalachian Mountains and surrounding uplands, and is composed of volcanic basalt and sedimentary rock in faulted and tilted layers many hundreds of feet thick.
context_section_description: The Metacomet Ridge is the result of continental rifting processes that took place 200 million years ago during the Triassic and Jurassic periods. The basalt (also called traprock) crest of the Metacomet Ridge is the product of a series of massive lava flows hundreds of feet thick that welled up in faults created by the rifting apart of the North American continent from Eurasia and Africa. Essentially, the area now occupied by the Metacomet Ridge is a prehistoric rift valley which was once a branch of (or a parallel of) the major rift to the east that became the Atlantic Ocean.
  Basalt is a dark colored extrusive volcanic rock. The weathering of iron-bearing minerals within it results in a rusty brown color when exposed to air and water, lending it a distinct reddish or purple–red hue. Basalt frequently breaks into octagonal and pentagonal columns, creating a unique "postpile" appearance. Extensive slopes made of fractured basalt talus are visible at the base of many of the cliffs along the Metacomet Ridge.
  The basalt floods of lava that now form much of the Metacomet Ridge took place over a span of 20 million years. Erosion and deposition occurring between the eruptions deposited layers of sediment between the lava flows which eventually lithified into sedimentary rock layers within the basalt. The resulting "layer cake" of basalt and sedimentary rock eventually faulted and tilted upward (see fault-block). Subsequent erosion wore away many of the weaker sedimentary layers at a faster rate than the basalt layers, leaving the abruptly tilted edges of the basalt sheets exposed, creating the distinct linear ridge and dramatic cliff faces visible today on the western and northern sides of the ridge. Evidence of this layer-cake structure is visible on Mount Norwottuck of the Holyoke Range in Massachusetts. The summit of Norwottuck is made of basalt; directly beneath the summit are the Horse Caves, a deep overhang where the weaker sedimentary layer has worn away at a more rapid rate than the basalt layer above it. Mount Sugarloaf, Pocumtuck Ridge, and Mount Toby, also in Massachusetts, together present a larger "layer cake" example. The bottom layer is composed of arkose sandstone, visible on Mount Sugarloaf. The middle layer is composed of volcanic traprock, most visible on the Pocumtuck Ridge. The top layer is composed of a sedimentary conglomerate known as Mount Toby Conglomerate. Faulting and earthquakes during the period of continental rifting tilted the layers diagonally; subsequent erosion and glacial activity exposed the tilted layers of sandstone, basalt, and conglomerate visible today as three distinct mountain masses. Although Mount Toby and Mount Sugarloaf are not composed of traprock, they are part of the Metacomet Ridge by virtue of their origin via the same rifting and uplift processes.
  Of all the summits that make up the Metacomet Ridge, West Rock, in New Haven, Connecticut, bears special mention because it was not formed by the volcanic flooding that created most of the traprock ridges. Rather, it is the remains of an enormous volcanic dike through which the basalt lava floods found access to the surface.
  While the traprock cliffs remain the most obvious evidence of the prehistoric geologic processes of the Metacomet Ridge, the sedimentary rock of the ridge and surrounding terrain has produced equally significant evidence of prehistoric life in the form of Triassic and Jurassic fossils; in particular, dinosaur tracks. At a state park in Rocky Hill, Connecticut, more than 2,000 well preserved early Jurassic prints have been excavated. Other sites in Holyoke and Greenfield have likewise produced significant finds.
caption: Traprock layer above; sedimentary layer beneath. Defunct quarry, Plainville Connecticut
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