46 Geology and Mineralogy of a part of Massachusetts, dc 
90. Nacrite? 
On the mica-slate of Chester, is found a mineral, incrust- 
ing the rock, which may be nacrite. I have not been able 
to examine it minutely, and merely mention it. Easily fu- 
sed. It may be a new variety of stilbite, occurring as an 
incrustation—its colour is a dirty yellowish white. 
21. TremoLitE: 
Var. 1. Common. 
In flattened or bladed crystals in Great-Barrington, 
Sheffield, and New Marlborough in dolomite. At the 
last place, the dolomite resembles that at Kingsbridge, 
N. Y., and also contains augite. Though the dolomite 
of Great Barrington containing the bladed crystals is 
generally very friable, I have found a large rock, which is 
very hard, and contains the same kind of crystals with au- 
gite. They are found sparingly also in Pittsfield. In Mid- 
dlefield in large masses of aggregated flattened crystals 
with rhomb. spar. Emmons. ‘These crystals often pass 
off into a perfectly granular tremolite. This is a new and 
very distinct variety, and greatly resembles the white cocco- 
lite of Phillipstown, N. ¥. opposite to Newburgh and a few 
miles from the river; but the product of fusion proves our 
mineral to be granular tremolite. ‘The constituents of coc- 
colite and tremolite are nearly the same, and the two min- 
erals seem to be nearly related. The locality, at which 
the bladed crystals are abundant, is in Muddy Brook in 
Great Barrington, three miles from the plain in Stock- 
bridge, and on the left of the road leading to New Marl- 
borough. In this friable dolomite I have found oblique 
four sided prisms of tremolite, which were friable, but har- 
dened somewhat, like the dolomite, on exposure to the air. 
They are probably the primitive form of tremolite. 
Var. 2. Fibrous. 
In Lee, Sheffield, Salisbury, and Canaan, Con. The 
masses, whose fibres are sometimes more than two feet 
long, contain parallelopipeds of sulphuret of iron. 
