PEGMATITE. 323 



several g-enerations and of every size until th6 original granite almost dis- 

 appears, and they appear in great numbers also far beyond the great granite 

 stocks, in the schists. 



While rauscovite is so rare as to be almost an accessory in the granitite, 

 biotite is not wholly wanting here, but appears always with the distinct 

 habit of an accessory, in great blades touching each other so as to form a 

 rude cellular structure. This was called pseudomorphous granite b\- 

 Hitchcock. 



PROBABLE EXTREME MODIFICATION OF THE PEGMATITE BY CRTTSHING. 



The North Amherst granite. — This is a peculiar rock, appe^ariiig in the 

 hills southeast ami west of North Amherst station, and again at the foot of 

 the west slope of the Pelham ridge east of D. Hawley's, beside a brook. 



It has at times a quite marked foliation (almost certainly a secondary 

 structure), distant })lanes being thickly covered with quite coarse muscovite- 

 biotite films, while in cross-section it appears wholly free from mica and 

 has a subporphyritic look. Opaque, subangular portions of feldspar or 

 quartz-feldspar are scattered quite distantl\- in a highly crystalline and con- 

 tinuous quartz mass which seems a secondary constituent cementing the 

 brecciated fragments of a highly feldspathic gi-anitefrom which most of the 

 hornblende or biotite has been removed during the violent changes the 

 rock has undergone. 



In thin section a few twisted fragments of much altered biotite appear. 

 The feldspars are brown with alteration products — rust, kaolin, and musco- 

 vite — and rarely determinable; more plagioclase can be made out with the 

 lens in the mass than under the microscope in thin section. The grains are 

 much cracked and crushed, and show undulatory extinction and wavy twin 

 lamina?. Everything' accords with its position along the main fault area 

 marked by strong crushing. 



ALBITK" GRANITE AND PEOIATITK DIKES CONTAINING; KARE 



MINERALS. 



It is a remarkable fact that the rare elements appear only in pegmatite 

 dikes on the extreme periphery of the great granite area, and that they are 

 not found in the bit^tite-g-ranite or within the great central region of granite. 

 This is enforced by the list of localities below, and may be brouglit into 



