THE LEVERETT- AMHERST AKEA. 223 



It remains to discuss the rock itself and see how far it still shows ]»oints 

 of resemblance to the calciferous mica-schists. 



The rock appears in Mount Warner, iu an area north of South Am- 

 herst, beneath the till in the ridge from Amlierst villag-e to North Amherst, 

 and in the rocky region along the north line of the town and extending 

 over into Leverett. It is everywhere greatly cut by granite dikes and 

 thoroughly im})regnated with granitic material, especially in the latter area, 

 where it exists only as shreds in an almost continuous expanse of granite. 

 This is clearly the eastern border of the great granite area which has its 

 center in Williamsburg, on the west of the valley, and extends thence east 

 beneath the Trias and finds its eastern border closely coincident with the 

 Conway mica-schist in which it has its whole development. 



Descriptiou. — The rock is in composition a gneiss, in texture a coarse 

 schist, so that Dr. Hitchcock sometimes gave it one name and sometimes 

 the other. It varies from a coarse muscovite-schist, made up almost wholly 

 of mica in large scales, to a schistose gneiss, at times containing large 

 rounded masses of fine microcline. It is always rusty, and very generally 

 contains pyrite, so that the water from several wells along the western 

 border of Amherst, when low, curdles milk and gives strong reaction for 

 sulphm-ic acid, and in new opening-s fissures of the rock are covered with 

 fine sheets of pyrite of very recent origin. 



Along the western edge of the ridge, appearing in my well on the 

 Northampton road, and in that of President H. H. Groodell farther north, 

 as also in Mount Warner, is a band the lamination surfaces of which are 

 spangled with large, rounded, equidistant plates of silvery muscovite filled 

 with fine radiated needles of fibrolite, a peculiarity which appears on a 

 much more extensive scale in the more easterly bands of the mica-schist. 

 This fibrolite occurs where the road over Mount Warner rounds a rocky 

 spur at the southwest corner of the mountain, and this is the most western 

 appearance of fibrolite in the schists. 



In excavations at the north end of Prospect street, in the hill east of 

 North Amherst railroad station, and in the large outcrop near South Amherst, 

 there are intercalated beds of an eclogite-like I'ock, a massive quartz-garnet- 

 hornblende rock containing shining scales of graphite. The garnet is light- 

 red, and is intimately mixed with the quartz to form a groundmass which 

 the hornblende ])enetrates in stout, parallel rods, transverse to the bedding-. 



