342 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



the original quartz grains. The structure seems, however, in general much 

 more like that of agate. It contains much opal. 



Pelham, south line, 40 rods east of western road. A coarse, schistose, 

 hornblende-gneiss; coarse, wavy cleavage sm-faces of hornblende make up 

 foliation faces, luster-mottled by rounded grains of fresh white feldspar, in 

 which cleavage is feebly developed. In section the hornblende is in large, 

 fresli plates, exactly like the few developed in the section last described ; it 

 shows deep colors, weak pleochroism, and is much cracked and twisted by 

 pi'essure. The feldspar is very fresh, and shows a great A^ariety of triclinic 

 striation — very broad to very narrow bands with perfectly parallel sides, 

 and tapering, interrupted, and offset bands; also bands wavy and contorted 

 by 231'essure and associated undulatory extinction. In one crystal, cut at 

 right angles to P (001), all the laws of twinning are beautifully developed. 



Belchertown, northwest corner, 40 rods east of R. Thayer's. A green 

 granitoid rock of medium grain, mottled with flesh-red from decomposed 

 feldspar; distinctly foliated. In section broad hornblendes much crushed, 

 feldspars crushed, showing undulatory extinction, much kaolinized, many 

 triclinic, with small extinction angle; much chlorite and epidote, the latter 

 often with distinct crystal faces externally, but with rounded zonal struc- 

 ture internally, the spherical center extinguishing first and then successive 

 zones in order to the surface, with revolution of 17°. 



A little farther south, on same band, north of house of A. Goodale, the 

 wholly crushed and altered rock is hornstone-like, with a dull mottling of 

 greenish and flesh color. In section the bisilicate is almost wholly removed, 

 and the quartz-plagioclase mass is wholly crushed, with wavy extinction 

 and twisted twin laminge. This is the south end of the "Shay's flint" band. 

 Followed 40 rods east, its contact on Pelham gneiss is seen. There is a 

 hornblende-biotite-gneiss for a rod at the contact, and the Pelham gneiss 

 is full of granite dikes. 



DIOBITE. 



North Prescott and New Saleoi. — A great oval area of diorite, 3 miles 

 long from north to south and about a mile wide, lies across the line sepa- 

 rating the above towns. It is a resistant rock, and makes the whole of 

 Packards Mountain in the latter town. It is surrounded on all sides by 

 the gneissoid quartzites, which dip uniformly to the west, undisturbed by 

 the intrusive rock. On all sides as one approaches the mass the quartzite 



