43^ STRATIGRAPHICAL GEOLOGY. 



4. Qltartzite. 



The quartzites in the Helderberg area are gray, white, and bkie, in dif- 

 ferent localities, and are very abundant. They are often quite friable 

 sandstones, and again approximate to the usual vitreous variety most 

 common in the Coos group. Whether they belong to more than one 

 series, remains to be proved. 



The first range to be described seems to skirt the Vernon and Hins- 

 dale gneiss area, bordering it almost everywhere. In the north-west part 

 of Hinsdale, about half a mile south of the Brattleboro' bridge, we find 

 bluish quartzites (Nos. 83, 84). At a quarry the dip is east. Farther 

 south it adds mica to its composition, and has a slaty color. At a shanty 

 near G. Thomas's is a little slate with it, dipping east, and then standing 

 vertically. The quartz continues along the river bank till we reach the 

 hornblende just opposite the mouth of Broad brook. It may strike 

 across the south-west spur of Wantastiquit mountain to the valley of Ash 

 Swamp brook. Nos. 71-75 represent the quartzite from one mile south 

 of H. Streeter's north to the line between Hinsdale and Chesterfield, 

 Daniel's mountain is composed of it, lying to the east of the stream (Nos. 

 ^6, yy). Next we see it a little north of the saw-mill near S. Thomas's, 

 between Daniel's and East mountains. The dip is 60° N. 60° W., over- 

 lying hornblende schists, and followed by staurolite schist dipping east. 

 The map would seem to imply the existence of a separate range from 

 No, 71 to the saw-mill, resting upon the gneiss, and perhaps not connect- 

 ing directly with what succeeds. A little south of the summit of Bear hill 

 is an easterly-dipping quartzite, which has been traced more than a mile 

 a little west of south, just overlying hornblende rock. The range is seen 

 farther south, at A. H. Sumner's. Another exposure is in the east part 

 of the village of Hinsdale. We have no well defined quartzite along Fox- 

 den mountain, south of Hinsdale village, though its components are largely 

 of silica. The range may reappear on the south side of Great brook, with 

 the dip of 80° N. 30'' E. It probably crosses the Connecticut near South 

 Vernon bridge to join the quartzites at the railroad cut on the state line, 

 and also nearer the Connecticut. The dip may be 20° N. E. at the cut, 

 but much higher near the river. About two miles south of the Great 

 brook locality, at a saw-mill in Northfield, is a quartz conglomerate (No. 



