478 GEOLOGY OF OLD HAMPSHIEE COUNTY, MASS. 



hxvcre spheres, and in the lorown ledges visible from this road off to the 

 south, whose ragged mass is made up of large angular pieces of the trap 

 cemented by finer dust of the same material. 



Here, in the north of South Hadley, the bed has great width, and across 

 to the north, at the top of the fine cliffs of buff' sandstone which overhang 

 the entrance to the brook gorge reached by H. White's wood road, just east 

 of the school and at the highest point of the ridge, the base of the tuff and 

 its junction with the underlying sandstone is instructively shown. In a 

 vertical wall of the pale-buff sandstone the lower half is comjjosed of the 

 usual coarse granitic sand, and above a large number of angular masses of 

 the trap, of the size of one's list and larger, are scattered at some distance 

 from one another in the same buff sandstone, while a few feet higher up 

 the rock is deep rusty-brown tuff. 



These fragments are manifestly the first and farthest-thrown products 

 of a distant exjDlosion, as the perfectly classified material of the sandstone 

 below and around the fragments indicates a current capable only of moving' 

 coarse sand before and during the time when these large angidar masses 

 were dropped here, to be followed b)^ so great a supply of trap debris that 

 the granitic sand almost disappeai's in it. 



Still farther west, whei'e the bed runs to a point on the south of the 

 Black Rock dike, it is a loosely cemented, mass of trap grains, all of the 

 size of large peas. From this point west to the Connecticut it is replaced 

 by the Black Rock dike, and on the west of the river it appears in the 

 cutting south of the point where the road crosses the railroad, below Mount 

 Tom station (Lymans Crossing), as a coarse trap agglomerate resting 

 directly on the trap, and except where it is interrupted by the leather-mill 

 fault it appears in the roadside all the way to the Holyoke line. The 

 blocks are a foot across, and in the fine-grained matrix a great number of 

 graphite scales occur. 



Just south of the cemetery north of Smiths Ferry, by the roadside, the 

 great blocks of the trap, nearly 2 feet long, cemented by the finer frag- 

 ments of the same material, can be seen to rest directly upon the surface of 

 the coarse rusty sandstone, and to have sunk into its upper surface as they 

 fell. Very little foreign material can be found here in the finer portion of 

 the tuff, but it seems never wholly wanting, and the graphite and muscovite 

 scales are never absent. 



