214 B. K. Emerson — Northfieldite. 



a thick bed of quartzose rock (northfieldite) adjacent to the 

 granite and a thinner upper bed perhaps 50 feet thick of a 

 coarse highly muscovitic pegmatite schist. It is always highly 

 garnetiferous and sometimes the garnets are an inch across, as 

 where the road going east from Sky Farm crosses the band. 

 This dips conformably beneath a sedimentary hornblende schist 

 that passes upward into a clearly sedimentary quartzite and is 

 itself clearly sedimentary, so that for a long time I considered 

 the whole series including the pegmatite schist and northfieldite 

 to be sedimentary. This double band is terminated on the 

 main fault and following that fault south to where it borders 

 the Connecticut at the "French King" near the mouth of 

 Millers River the pegmatite schists appears again along the 

 bank for a mile. 



Several of the great pegmatite stocks farther south show in 

 part the same bordering pegmatite schist facies, as at the south 

 end of the great stock just north of New Salem village, 

 described below. Indeed I have mapped a broad band run- 

 ing from "West Orange north through Hockanum Hill as 

 pegmatite, which then passes into a coarse pegmatite schist by 

 loss of its feldspar and continues in a narrow band north for 

 seven miles. On Osgood Brook in Wendell is an oval stock 

 of coarse pegmatite having a border of the same coarse highly 

 muscovitic quartzite. Indeed, the other great pegmatite beds 

 in the region are closely allied with the northfieldite beds here 

 described, and are often in part quite greisen-like. 



A few rods west of the highest point in the road east of Mt. 

 Toby in Leverett, just south of which the road to Mt. Toby 

 turns off, one can see the coarse pegmatite grade into a great 

 mass of this coarse quartz rock or northfieldite.. It is quite 

 possible that they also may pass downward into a granite like 

 the Pelham and form a pegmatitic phase in the latter, as much 

 of the Hubbadston gneiss further east is a superficial pegmatitic 

 phase of the Fitchburg granite. 



The other type of the northfieldite is the rock forming the 

 crest of Mt. Orient in Pelham, where it is 120 feet thick and 

 present in considerable areas in that town and in Shutesbury 

 as a superficial portion of the Pelham granite-gneiss. It con- 

 tains more than 93 per cent of silica and has the aspect of a 

 slightly actinolitic or biotitic quartzite or an extremely 

 quartzose aplite. 



When the gneiss was thought to be an altered Cambrian 

 conglomerate the quartzose upper layer was thought to be the 

 equivalent of the Cheshire quartzite (see Mon. xxix, U. S. Geo. 

 Sur., p. 45). The banking of the gneiss is in a broad arch with 

 low dip to east and west, and the northfieldite forms generally a 

 superficial layer on the gneiss and the transition of the one into 



