thick, and known in Connecticut as "the posterior sheet," or in Mass- 

 achusetts as the Hampden trap, and extends north as far as the 

 Holyoke Range. This period was followed by a continuation of the 

 volcanic activity, when explosive eruptions took place and the next 

 200 feet or more of sands are mixed with greater or less quantities of 

 volcanic ash. Above this there are still some thousand feet of sands 

 mostly of finer character than the earlier deposits, until the valley 

 was filled. 



After the accumulation of these sandstones and lavas, probably 

 in the Jurassic, a second period of faulting took place, breaking the 

 Triassic deposits and adjacent crystalline rocks into a complex of 

 smaller blocks, and tilting these at various angles, but mostly so 

 that the blocks dip to the east. Some blocks just south of Amherst 

 were caused to dip south, and the block or blocks of the Amherst 

 region were lift higher than the others. This is the block mountain 

 period of the region. 



During the remainder of the Jurassic and through Comanchian 

 and Cretaceous times, all the New England country, both the 

 eastern and western highland and the Connecticut Valley block 

 mountains, was being eroded to a great plain near sea level, the 

 Cretaceous Peneplain, regardless of the hardness of the various 

 rocks; excepting only the monadnocks mentioned above. 



During the latter part of the Cretaceous, the New England 

 peneplain experienced a broad uplift (not entirely uniform), amount- 

 ing in the Amherst region to about 1200 feet. This rejuvenated 

 the streams and they began again to carve out valleys, and carry 

 the loosened material away to the sea. The Triassic sandstones 

 were relative soft and were rapidly removed down to about sea level, 

 at which level a new plain began to be formed, about as extensive as 

 were the Triassic deposits. The trap layers, which had been tilted 

 about in the Jurassic block-forming movement, when uncovered, 

 were more resistant and so stood out as mountain ranges in the 

 valley, the exposed edge making generally north aud south ridges 

 with the steep slope to the west and the gentle slope to the east. 

 Thus the Tom Range and Talcott Mts. and the Pocumtuck Ridge 

 came into existence. The blocks tilted toward the south, when 

 eroded, uncovered the east and west edge of the trap layers and 

 therefore made an east-trending ridge, the Holyoke mountains. 

 For ten miles north of this range the blocks had been lifted so high, 

 that the Triassic material was mostly carried away and where 

 Amherst stands (including Mt. Warner and a strip to the north of 



