THE CHESTEE AMPHIBOLITE AND SERPENTINES. Ill 



and the light bauds are placed at 45° to the plane of the instrument. Parallel 

 with this plane they are black. They show an extremely hue, transverse, 

 fibrous structure. The intervening lens-shaped fields, dark in the drawing, 

 are black in this position at 45° when the bands are white; when rotated to 

 0° they show white, radiate-fibrous tufts on a black ground of nonpolarizing 

 seipentine. 



The deposition of magnetite in certain of the places of perfect clea\-age 

 was accompanied by the very regular change to fibrous serpentine growing 

 out from the planes and forming the white bands. Then the growth of 

 secondary serpentine between some of these bands has seemingly wedged 

 them apart, and given them their curved forms and })roduced the lenticular 

 fields of serpentine. 



14. "■ Serpentinr (\M\\\({i^.v). Blandford." XIII, No. 11, Mas.sachusetts 

 Survey Collection, 1841 ; No. 880, 1835.— Compact, fresh surface, bluish- 

 black, mottled with dull brownish-black; contains much magnetite; is unlike 

 any other serjientine known by me from this region, and comes, doubtless, 

 from the bowlders noted by Dr. Hitchcock on the east line of the town.* 



With the lens the slide is seen to be mottled with large green spots, which 

 were doubtless formerly enstatite and which retain its structui'e, though com- 

 pletely changed; and in other spots traces of an olivine network can be made 

 out with much probability. The rock is, however, for the most part com- 

 pletely changed, and shows everywhere the softly colored })olarization of talc. 



15. Enstatite-serpcntine. — Atwaters, Russell. Following the hornblende 

 band northward to the point where it bends round through the southeastern 

 corner of Blandford, whei'e I suppose the above specimen No. 11 of the 

 Massachusetts Survey Collection was obtained, we come upon the great out- 

 crop in the high hill in Russell overlooking the Westfield plain, where many 

 years ago the rock was quarried extensively as black marble by Mr. Atwater, 

 the father of the present proprietor. 



The black serpentine presents no peculiarities by which it can be dis- 

 tinguished microscopically from the other localities in Granville and Russell. 

 Because of the deep quarrying the finest specimens can be obtained from 

 this place, and the bastite is of a beautiful apple-green color, instead of the 

 pale gray seen elsewhere, and was found by Tschermak to have the low 

 angle of 30° for the optical axes. 



' E.Hitchcock, Geol. Mass., 1841, p. 617. 



