290 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



area colorless or faintly flesh-colored. This border is interrupted as if 

 of later and irregular growth on the sharply defined brown prism, but 

 is of the same optical orientation as the latter. It seems to me to be 

 rutile coated with leucoxene. 



10. Hornblendic limestone; from upper surface of the magnetite at 

 the opening north of the large quany, Williams farm, Bernardston, and thus 

 directly above the main limestone. An impm-e limestone, effervescing 

 abundantly; dull, mottled, blackish-gray, glistening with cleavage faces of 

 minute hornblende crystals, rusting deep brown. 



In the thin section a colorless ground appears, with few magnetite 

 grains and many hornblende needles, often aggregated into compound 

 crystals of considerable size, and changing in small amount to chlorite. 

 The hornblende is also often fasciculate and in feathery groups, and shows 

 veiy weak pleochroism. The ground consists of much twinned calcite 

 grains, with some quartz and feldspar. 



AMPHIBOLITE ASSOCIATED WITH THE LIMESTONE IN THE GNEISSOID QUARTZITE. 



11. Amphibolite from South Vernon limestone locality. Immediately 

 adjoining the limestone on the north is a coarse hornblende rock, dark- 

 gi'een with blotches of white, consisting of a granular quartz-feldspar mass, 

 and canying in fissures miinite attached plagioclase crystals. 



In sections the large hornblendes are almost free from color and pleo- 

 chroism and are composed of groups of needles, sometimes fasciculate, 

 sometimes gathered into large, well-outlined individuals, and entirely unde- 

 composed. There is only a trace of effervescence and that is confined to 

 the hornblende. 



12. Amphibolite from South Vernon, south of road at E. G. Scott's, 

 opposite the limestone. A greenish-gray, fissile rock, resembling a fine- 

 grained gneiss. The lens shows many fresh cleavage surfaces of plagio- 

 clase and pale "luster-mottled" hornblende. 



In section the large hornblendes inclose many grains of plagioclase, 

 rutile, and magnetite; they show marked dichroism; b> jc> a; jc = emer- 

 ald green, b = olive, a = yellow; extinction at 21°. Leucoxene is in aggre- 

 gates of grains nearly colorless or with red-bi-own centers; rutile occurs in 

 square prisms. Fine, large, pale-reddish titanite crystals show positive bisec- 

 trix and axial figure parallel to co P c6. The whole colorless background is 

 made up of limpid granular plagioclase, often twinned but more often free 



