TOXALITE. 339 



very full of cavities with moving bubbles, many of the cavities containing 

 water and carbon dioxide and a moving bubble of the latter. 



The feldspar is uniformly very much more decomposed than tlic appear- 

 ance of the rock would lead one to suspect. Sometimes the change is into 

 kaolin, sometimes into nuiscovite. The change is always central, and at 

 times a sharply defined diamond-shaped area of cliange occurs in a sc^uare 

 crystal. This change is so general that it can only be determined that the 

 feldspar is for the most part triclinic, with extinction at small angles. 



The hornblende is often twinned, and extinguishes at high angle — 

 19°-2r. 



Epidote, in minute groups in tlie chlorite, and titanite are abundant in 

 the Whately bed. 



Allanite is frequent, especially in the Hatfield Ijed, in crystals visible to 

 the eye, and surrounded by the peculiar radiate puckering or splintery 

 fracture common around this mineral. Under the microscope it is at times 

 surrounded by epidote. 



In the Hatfield mass the biotite is subordinate and the rock agrees 

 exactly with the tonalite of the Tyrol. In Belchertowu it is more biotitic. 

 In the latter area, in the region around Three Rivers, the quartz is ame- 

 thystine and contrasts beautifully with the green diallage. This variety 

 shows under the microscope a beautiful granophyre structure. Farther east, 

 in South Belchertown, large bowlders on the railroad show a coarsely por- 

 phyritic development of the biotite, each of the large scales being surrounded 

 b}' a white border, and the quartz in this variety is violet, like the pre-Cam- 

 brian gneiss in the western portion of the State. 



THE CRUSHING AND ALTERATION OF THE TONALITE ALONG THE PELHAM 



FAULT. 



The outcrops of the tonalite which appear in the line of the great fault 

 at the foot of the eastern plateau from Belchertown to Leverett are greatly 

 altered by the movements which have taken place along that line. Follow- 

 ing the road west from South Leverett to the point where an unused road 

 goes east to the old cemetery, one finds a large outcrop of a beautiful dark- 

 gi'een chloritic tonalite, in which the reddish feldspar contrasts finely with 

 the dark hornblende, and the contrast is heightened by a network of fine. 



