448 GEOLOGY OF OLD HAMPSHIEE COCTNTY, MASS. 



southwest far down behind the continuation of the bed, which, starting 

 again in the small cone, Rattlesnake Knob, runs on westwardly thi-ough 

 Norwottuck. Bishops Mountain is a high isolated ridge.^ 



This fault is, on the eastward face of the small cone, marked by an 

 almost vertical wall, nearly a hundred feet high, and climbing this wall 

 one finds midway a naiTow shelf, composed of the sandstone resting against 

 the trap. The sandstone is not baked, nor is the trap amygdaloidal, nor 

 aphanitic, but of the grain usual to the central portion of the bed. It is, 

 however, brecciated at the contact by crushing and recemented by silica, 

 as can be seen by digging at the southeast corner of the narrow flat. 



Westwardly the heavy vertical bluff continues, deeply notched at the 

 "Notch" and the "Low Place," until, after presenting for several miles its 

 vertical wall to the north, it sweeps down in a magnificent section, nearly 

 at right angles to its dip, from the height on which the Holyoke House 

 stands, past Titans Piazza with its fine columns, to Titans Pier, where it 

 plunges beneath the waters of the Coimecticut to rise on the west side of 

 the river to the top of Nonotuck in a section which is the counterpart of that 

 on the east. 



The Notch is produced by erosion on a northwest-southeast fault, with 

 uptlirow on the east, which causes the fine northeast bluff of Bear Moun- 

 tain on the west of the notch road and the equally marked southwest bluff, 

 which stretches away southeast on the southern aspect of the range east of 

 the road. 



That the Holyoke and Mount Tom beds are connected beneath the 

 river admits of no doubt. As one stands below Titans Piazza, midway in 

 the Mount Holyoke section, and looks across the river, the Mount Tom 

 section opposite is seen to be the exact counterpart of the former, and from 

 the two mountain houses which crown the crests of the ridges on either 

 side of the river the massive beds sink down southwardly, and agree in 

 the character of the sandstone beneath, in the amount of its baking by the 

 bed, and in the character and tliickness of the trap itself. The Holyoke 

 ridge ends in Titans Pier, whose vertical walls rise 65 feet above the water, 

 and at exactly the corresponding point on the opposite bank the trap 

 appears and runs west in a heavy ridge across the low terrace flats and, 

 turning, mounts up to the crest of Mount Nonotuck and forms the high 

 continuous ridge to its culmination in Mount Tom. 



' The contours of the map are here quite incorrect. 



