THE PELHAM AND WILBRAHAM AREA. 



49 



toward the latter and then somewhat confused, but distnictly traceable far 

 into it and dving- out <»-raduallv by the slow disappearance of the biotite 

 and ([uartz, until the whole of the great projection is made up of a mass of 

 snow-white, extremely fine-g-raimlar, massive anorthite, carrying toward its 

 borders a large quantity of black tourmaline in great irregular l)unches, 

 which, at the apex of the mass, atft)rds Ijlocks of pure, coarsely crystalline 

 tourmaline over 2 feet across. The fluorine of the biotite has gone into 

 the tourmaline. Many small crystals of allanite are shot through the 

 anorthite, and when In-oken across the latter mineral shows the usual 

 puckered surface radiating from the allanite. 



, 3. G, corundum 



FlO. 4.— West wall of Pelham asbe3t03 quarry=right half of fig. 3, qnarried deeper. Letters as in flf 



uodules: H. apatite. 



The tourmaline breaks into large imperfect crystals, often 8 to 12 

 inches long, and in cavities shows terminations always with broad P 

 l)lanes. It contains, in cavities between crystals, zoisite, apatite, and beau- 

 tiful geniculate twins of rutile, together with perfect apatites alone in other 

 cavities and in the mass itself. Under the microscope it often shows an 

 exquisite micropegmatitic intergrowth with the anorthite, the latter taking 

 the place of the quartz in graphic granite, while the tourmaline is extin- 

 MON XXIX 4 



