after which a second disturbance in the Devonian folded them again 

 and lifted the Berkshire region far above sea level. This system of 

 mountain ranges remained until eroded to the level of the Cretaceous 

 peneplain, some elevations however remaining on that plain as 

 monadnocks, like Grey lock; and the Green Mountains. 



The eastern upland is the southern extension of the White Moun- 

 tain highlands south through Massachusetts and Connecticut, and 

 consists of igneous and metamorphic rocks of Cambrian to Penn- 

 sylvanian age, folded into a mountain system during the Penn- 

 sylvanian. Through the succeeding time down to the Cretaceous 

 these were reduced toward the level of the Cretaceous peneplain. 

 Again some points were left above the plain, such as peaks in the 

 White Mountains, Mt. Katahdin in Maine, Mt. Monadnock in 

 New Hampshire, and Mt. Wachusett in Mass. 



The Connecticut Valley lowland differs greatly in its history. 

 Some time in the Triassic epoch a series of great faults developed in 

 Eastern North America. Between some of these great faults great 

 blocks dropped down, in Nova Scotia, in Connecticut and Massachu- 

 setts, and in New Jersey and Pennsylvania. The Connecticut 

 Valley approximates one of the great rift valleys thus formed. Just 

 how deep the valley was at any one time can not be said, for probably 

 the down dropping block took its final position as the result of a 

 series of movements; but to fill the hole thus formed, it took some 

 10,000 feet of deposits. Of course as soon as such a valley was 

 formed, gravel, sand and clay was washed in from the sides, and the 

 filling began. The coarsest material is near the sides, the finer near 

 the middle. Most of the fill is conglomerate and sandstones, but 

 there are bands of shale, some of it blackened by organic matter. 



In general the first part of the fill is conglomerates and sandstone, 

 varying from some 300 to over 1000 feet in thickness. When this 

 had been laid down volcanic eruptions toward the south end of the 

 valley produced a sheet of lava, some 250 feet thick in the south and 

 thinning out until it is lacking above the Massachusetts line. In 

 Connecticut this is termed the * 'anterior sheet." Above this there is 

 a further fill of 2000 to 3000 feet of conglomerates and sandstones, 

 on top of which were poured out the ''main sheet" of lava (termed 

 in Massachusetts the Holyoke trap), a sheet generally 400 — 500 feet 

 thick, but thinner near the northern end of the valley. Another 

 period of in washing accumulated 1000 to 2000 feet more of sand- 

 stones, etc., followed by the third volcanic period when another 

 thinner layer was poured into the valley. This is 250 or so feet 



