22 



GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



wavy-beclded gneiss of fine grain and almost black from the abundance of 

 the black biotite. (See fig. 1.) Contorted white veins one-fourth inch to 2 

 y inches wide run through the rock, high up in the cutting, 



with most tortuous course, and on the soutli side I could 

 recognize the spot whence came a great block which has 

 long lain in front of the geological museum at Amherst and 

 whose origin I had been unable to learn. These "veins" 

 are formed by the expulsion of the biotite from their area, 

 the white quartz-feldspar mass being continuous within 

 and without their limits. 



The black gneiss abuts, apparently by a fault, cer- 

 tainly by a wholly abrupt transition, upon a band of the 

 coarse white, almost micaless, Hinsdale gneiss, 23 feet wide 

 below, but naiTowing above. This is followed by a bed 

 of white, thin-bedded, highly crystalline chondrodite-lime- 

 stone, with thin films of serpentine, forming a beautiful 

 veixl antique, which is separated by 108 feet of the same 

 black Lee gneiss from a second band of a similar limestone, 

 of Avhich only 29.5 feet are exposed. This is followed in 

 the brook bed at bridge 142, and on through the cutting, 

 by a large mass of the dark gneiss, carrying beds of 

 hornblende-schist, until we come, at the fourth telegraph 

 pole from bridge 142, upon the fine unconformity where 

 the conglomerate-gneisses mount upon the dark Lee gneiss. 

 Between this point and the Bancroft station the cut- 

 tings expose a long extent of contorted and twisted rocks, 

 where the beds swing round from horizontal to vertical 

 within a few feet. Gradually a low dip eastward pi'edomi- 

 nates, and this becomes steeper, and a band of hornblende- 

 gneiss 10 feet wide sets in, and at the eighth telegraph 

 pole from the station, just at the signal house, a boss of 

 coarse actinolitic rock derived from the older limestone 

 protrudes. All east of the unconformity is Becket gneiss, 

 ^ except the few hornblende-gneiss masses and the last- 



mentioned boss of actinolitic rock, which are brought just above the railroad 

 level by the undulations of the Becket gneiss. 



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