Geology and Mineralogy of a part of Massachusetts, &c. 41 
Subsp. Pycnite. 
In Chester in detached pieces of gneiss; colour bluish 
ereen,—six-sided prisms, terminated by planes, with the an- 
gles truncated—imperfectly foliated perpendicularly to the 
axis, lustre of lateral planes vitreous—infusible, sp. gr. to- 
wards 4.0—less hard than Bery] which it resembles—larg- 
est crystals an inch and a half long, and half an inch in di- 
ameter,—several prisms sometimes united parallel to each 
other. Emmons. 
6. SILICEOUS SLATE, 
In rolled masses in Berkshire county. In beds in trans- 
ition argillite, Troy, Hudson, &c. 
Var. Basanite. 
In Williamstown —rolled pieces. 
W. MICA. 
Var. 1. Lamellar. 
Of various colours, along the eastern range of mountains. 
Sometimes green at Cummington. Porter. 
Var. 2. Prismatic. 
In ‘Chester, in coarse granite with the preceding. It 
occurs in fine filaments which gradually pass into rhombic 
prisms. Emmons. It is abundant and beautiful. Also in 
Worthington. The fibres are often “as delicate as those of 
amianthus.”? This mineral, found also in Saratoga coun- 
ty, heretofore rare, has now become plenty. 
Var. Plumose. 
This name which has often been applied to some varieties 
of mica, is intended as descriptive of the mineral. The fi- 
bres are not easily separable, like the prismatic, and diverg- 
Vou. VIII. No. 1. 6 
