THE PELHAM AND WILBRAHAM AREA. 51 



mass, splitting in a direction at right angles to tlie walls, and pearl-gray 

 when not blackened by manganese. 



More rarely the vein filling is completely asbcstiforni and tlu* fillers 

 cross the vein from side to side; very often they are all bent soinewliat to 

 one side or the other as they approach the wall, being compressed by tlieir 

 own growth. 



In other parts of the excavation these veins have swollen to much 

 greater width, and great ligniform masses, 20 to 30 inches in length, have 

 been excavated. This is the "asbestos" of the ((narry, and manA- hundred 

 tons have been excavated and sold for grinding into paint and for asl)estos 

 papers. The resemblance of this strnctnre to the well-known microscopic 

 olivine network is extremely striking, and it wonld seem diificult to avoid 

 the conclusion that the anthophyllite here must be of secondary origin and 

 a derivative from the olivine, probably under conditions of considerable 

 pressure and heat, and therefore at an early period in tlie histor-^- of the 

 changes which the deposit has undergone. Its exact resemblance to the 

 transverse fibrous vein fillings of calcite, gypsum, and chrysotile will hardly 

 admit for it any essentially different explanation. 



The anthophyllite occurs also in large, rather coarse-matted fibers. It 

 polarizes very brilliantly and is quite fresh and limpid, tlie gra}^ color being- 

 due to fine magnetite dust. 



At the northern excavation and at the large opening tliere are sparingly 

 disseminated in the fresli olivine rock squarish plates, i to ^ inch across, of a 

 ])ale bronzy enstatite or bronzite, making an ordinary olivine-enstatite rock. 

 This is a primary bronzite. 



Masses of a bright emerald-green actinolite in matted fibrous arrange- 

 ment of the single crystals were j)roduced from the large opening, but 

 their relations to the other minerals can not now be observed. At a new 

 excavation made during the year 1883, near the south end of the bed, 

 a long band of this mineral was struck just below the drift, and resting 

 upon the thick decomposition layer of anthophyllite, in the midst of which 

 several thin layers of the actinolite also appeared. 



The biotite containing nodules of the dark-green hornlilende here also 

 folded deep into the saxonite, as at the large cutting. The anthophyllite 

 layer was followed in the bottom of the excavation by the usual black, 

 imdecomposed olivine rock. The biotite has also been attacked on a large 



