During the Triassic and Jurassic Periods, Pangaea began to break apart. This led to the formation of the Atlantic Ocean and a new mid-ocean ridge, along which much volcanic activity occurred. (Raymo, 1989)
Volcanism greatly changed the Connecticut Valley. Basalt flows and intrusions helped to form prominent landscape ridges, which directly impacted life in our state. Lava flows created dams, lakes and streams became larger and more plentiful. Connecticut’s environment became more friendly. (Little, 1986) The faults zones formed from Pangaea breaking up, created pathways for magma to seep toward the surface for 25 million years (between 171-196 million years ago). These lava flows (which would harden into basalts) oozed from the faults, allowing many animals time to escape their effects. (Little, 1986)
There were three major lava flows that covered the valley during Mesozoic times. These flows were between 150—320 feet thick. Between these lava flows, sediments eroded and piled on top of them. (Little, 1986)
One of the state’s major monuments to prior volcanic activity is the Holyoke Range. It is comprised of a series of flows, ash, layers of sediments. Its base consists of two basalt flows (320 and 255 feet thick). Pillow lavas and vesicular basalts, further evidence of volcanism can also be seen in our valley.(LIttle, 1990)
Three major pieces of volcanic activity—intrusions can be found close by. East and West Rocks in New Haven and Sleeping Giant in Hamden. All of these are quite familiar to New Haven students. This makes geology easier to teach and a field trip to one of these areas is quite worthwhile.
Sleeping Giant is a type of intrusive dike called a stock. this is the main line of a lava flow’s plumbing system. (Bell, 1985) It is exposed for three miles at its surface today. Sleeping Giant form when Pangaea broke apart. Magma had gotten trapped below the surface and pushed up through cracks and seams insedimentary rock. The magma hardened into traprock and when the Connecticut valley tilted east, so did the Giant. Millions of years went by and during this time erosion wore away the softer sedimentary rock around this intrusion, leaving it in the shape of a sleeping giant. (Wetherell, 1992)
East Rock, another intrusion when acquired by the city of New Haven has an interesting sideline. The owner of the rock ‘I had to be dispossessed against his will. He wasn’t too friendly to visitors and anticipatlng-a great-flood, had:built—a large open boat on top of the rock. (Longwell, Dana, 1932)
East and West Rocks are intrusive ridges, created by molten rock, that like with Sleeping Giant, pushed up into underground cracks and hardened into traprock. Erosion of the softer sedimentary rock around the basalt, helped to expose them. (Wetherell, 1992)
Both East and West Rocks formed from the same magma surge. West Rock starts out as an intrusive dike, but extends underground as a sill to East Rock. (Bell, 1985)
All this volcanic activity, has helped in shaping the life and landscape of Connecticut today. A field trip to one of the above mentioned intrusions came show this relationship to the students. In addition, glacial history can be shown and discussed, in part at one of these sites. The impact of the Ice Age in our state will be discussed later on.
