THE PELHAM AND WILBRAHAM AREA. 43 



To the south the rock is coarser than in the other areas, and in contact 

 with the great mass of the Belchertown tonahte is considerably ahered. 



In Wilbraham its attitude is nearly veitical, and it forms the core of an 

 anticHne which is slightly overturned to the east, as the di^is are high to 

 the west. 



At Power's mine, in Greenwich, on the high hill overlooking the house 

 of S. B. Estev, considerable blasting has been done upon a vein of coarsely 

 granular magnetite, containing much coarse red garnet and pyrite — au 

 entirely worthless deposit. 



PETROGRAPHICAL DESCRIPTIOK. 



1. Granitoid gneiss from Massachusetts Agricultvu-al College quarry, 

 Pelham. This may be taken as a type of the Monson gneiss. 



A very clear, fresh, gi-ay, sti-etched biotite-gneiss. It is a most crisp 

 and friable stone, shomug no ti-ace of decomposition, the fresh black biotite 

 appearing in the mixture of limpid quai-tz and feldspar. 



Titanite is an abundant constituent, and rai-ely a ti-ace of epidote 

 appears in the neighborhood of the biotite. The lens shows the jet-black 

 biotite scattered in an almost limpid gi-anular mass, with faint trace of 

 poi-php-itic structm-e and slight nacreous dusting. Under the microscope 

 the quartz shows swarms of minute inclusions, with groups of lai-ger cavities 

 ha^-ina■ mo^•ing bubbles. One grain alone was filled with long laitile needles, 

 and this had a slightly reddish shade. 



Orthoclase occurs in larger crystals than the other constituents and 

 includes rounded quartz grains. It is quite abundant. 



Microcline is abundant and of late formation, crystalUzed out so as to 

 cement a gi-eat number of qttartz grains. 

 Albite occm's rai-ely. 



The biotite is in separate black scales, and with the lens is seen to be 

 abundant, much notched and often extended to include several quartz 

 grains. 



Titanite is in angulai- gi-ains of the same size as the other constituents, 

 and in distinct crystals, pale greenish-brown exteriorly and deep red- 

 brown in the interior, the boundary between the two colors being generally 

 distinct, but in one case a red-brown crystal is inclosed by a pale-yellow 

 one, the two being of common orientation and the outer bounded by fewer 

 faces. 



