294 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



to 1)6 made up of long, interlaced, crystalline blades of hornblende running 

 in every direction and inclosing a great number of feldspar grains. The 

 hornblende has extinction = 27° and is strongly pleoclu-oic; ): = mountain 

 gi-een, a and b = yellow; one grain of plagioclase, extinction 20° on each 

 side of the twinning plane. Manj" sections from specimens taken from the 

 various beds between this point and South Vernon show precisely the same 

 structure, but generally contain grains of meuaccanite surrounded by 

 leucoxene. 



19. Amphibolite from West Northheld, from large outcrop rising above 

 the terrace sands east of the Bernardston-South Vernon road at the point 

 where the road branches off to the fen-y. A jet-black, schistose amphibo- 

 lite, the shining-black hornblende needles being arranged parallel to the 

 foliation plane, but in every direction in that plane. 



20. Ampliibolite from West Northiield, at first branching of the road 

 west of Northfield feny. A fine-grained, black rock, the fine black needles 

 aiTanged as in the last case. These two rocks resemble more closely the 

 older amphibolite of Northfield Mountain east of the river than the tough, 

 matted, fibrous, massive rock of the West Northfield range described above. 

 (In the Northfield Movmtain rock, liowever, the stretching is complete and 

 the rock thin-fissile, and the hornblende needles are all closely parallel to 

 one another. It is porphyritic, has the usual medium absorption and 

 pleochroism, c = blue-green, li = olive, a = honey-yellow ; extinction 19°.) 

 Under the microscope the needles are grouped in parallel or almost parallel 

 bundles to form large crystals, which resemble the large blades of the 

 range to the west, described above. The fine, fresh needles are often well 

 terminated, the pleochroism strongly marked; C:=^deep mountain green, 

 li= olive green, a = yellow. Beautifully complex, large reticulated groups 

 of magnetite crj^stals occvir, and with polarized light the colorless back- 

 ground breaks up into a fine-granular plagioclase aggregate. The lighter 

 spots show the usual untwinned plagioclase mosaic. The grains show the 

 usual concentric extinction; the rounded or angular centers extinguish in 

 one position, and the darkening goes outward to the surface with continued 

 rotation. 



21. Limestone; Bernardston, northeast of N. W. Purple's house (now 

 abandoned), on the Purple blind road. Layers of white granular lime- 

 stone up to 15™™ thick, in green, compact hornblende rock. 



