360 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



The conglomerates are concealed beneath the broad sand plains of 

 Montague, but rise in the great mass of ]\Iount Toby to their greatest 

 height and their most extensive development. The steep walls of the deep 

 gorge which borders this mountain on the east show sheer cliffs and enor- 

 mous bowlders of the coarsest conglomerate, and high above the liottom of 

 the valley, in the beds of Roaring Brook and of the next brook to the 

 north, the contact of this conglomerate on an ancient quartzite can be seen. 



This mountain is a slate-conglomerate from base to summit and from 

 its eastern slopes west nearly to the Connecticut. High up on its western 

 slope are two bands of fucoidal sandstone, which penetrate the mountain 

 with slight eastward dip, and indicate two horizons at which a deepening 

 of the water sent the hner sediment far east over the shoreward con- 

 glomerates. The high level (310 feet above the sea) at which the rocks 

 of the South Leverett plain pass beneath the conglomerate, and the rising 

 of the whetstone and amphibolite through it at Whitmores Ferrv, show 

 that the rock is not above a thousand feet thick. 



From jMount Toby to Belchertown Pond the shore conglomerates are 

 wholly removed by erosion. Some of the most interesting exposures of 

 the shore conglomerates on the east side of the valley occur in Wilbraham. 

 Just east of the academy, after passing a bend and slight rise in the road, 

 one comes upon outcrops of a dull-brown, rotted conglomerate, so soft that 

 it is dug into for road material. It is exposed along the south side of the 

 road for 80 feet. Just to the east a highly indurated muscovitic quartzite, 

 full of quartz veins and of dark color, rises sharply to form the eastern 

 escarpment of the valley. The conglomerate rests against this and only a 

 few feet of turf covers the line of junction. This is marked by a slight 

 depression which crosses the road obliquely, east of which the ground rises 

 rapidly and is covered by the large light-colored bowlders of the schist. 

 All or nearly all of the pebbles of the conglomerate, 1 to 8 inches long, are 

 from this schist. 



A medium- to fine-grained red sandstone occurs west of the conglom- 

 erate and can be traced in the bed of the road right up to the conglomerate, 

 where the two are seen only 2 or 3 feet apart, and the sandstone either runs 

 under the conglomerate or the two abut by an irregular fault. The latter 

 is by far the most probable, as the sandstone dips 15° W., while the con- 

 glomerate is horizontal, and the transition would be very aljrujit if the 

 sandstone went underneath. 



