110 SLATE DEPOSITS AND INDUSTRY OF UNITED STATES. 
on cleavage planes, or minute cub s on joint faces. That this mineral is pyrite and 
not marcasite is shown by its not decomposing readily after long exposure on the 
slate dumps.''' 
Rarely a little galenite occurs in the quartz veins. 
It will be observed that nearly all of the above minerals have already been men- ' 
tioned as occurring in the slates, as shown either by the microscopic or the chemical 
analyses. 
Benson black slate. — Half a mile east of Benson village and 7J miles north-north- 
west of Fair Haven, in Rutland county, black roofing slate was quarried in 1895, but 
the quarry was abandoned not long afterwards. The slate is of Ordovician age ( 1 1 udj 
son-Utica), and belongs in a shale, slate, and schist belt which extends nearly 4 
miles westto within a mile of Lake Champlain, and 4| miles south-southwest to the 
village of West Haven, and also, with bends and ramifications, 20 miles north-north- 
east to Weybridge Center, in Addison county. Almost the entire area and the quarry 
Location will be shown on the forthcoming Fort Ticonderoga folio, Economic geol- 
ogy sheet. The slate-bearing area, however, probably does not exceed 12 square 
miles. 
At the quarry the beds dip about east at angles ranging from 15° to 20°; cleavage 
strikes about N. 7° K., dipping east at 35°, and vertical joints strike N. 75° W. 
The slate is a bluish black; to the unaided eye has a somewhat fine texture and a 
s( miewhat smooth, slightly lustrous cleavage surface. It is carbonaceous or graphitic, 
contains a little magnetite, effervesces with cold dilute hydrochloric acid, is sonorous, 
and has a fair degree of fissility. 
Under the microscope it shows a matrix of muscovite (sericite), with a brilliant 
aggregate polarization, somewhat obscured by much carbonate and carbonaceous 
matter in fine and coarse particles. The quartz fragments measure from 0.013 to 
0.03 millimeter; carbonate rhombs from 0.004 to 0.035 millimeter. Pyrite spherules 
from 0.0017 to 0.007 millimeter number about 200 per square millimeter, often 
occurring in rows along the cleavage. Rutile needles from 0.0017 to 0.0952 milli- 
meter long are abundant; chlorite scales are very few and small, zircon fragments rare. 
The constituents of this slate, arranged in descending order of abundance, appeal 
to be muscovite | sericite I, quartz, carbonate, pyrite, rutile, carbonaceous or graphitic 
matter, and magnetite. 
This slate is thus closely related, both in composition and quality, to the "sof 
vein" slatesof Lehigh and Northampton counties, Pa. Its large amount of carbonai 
indicates its probable discoloration on continued exposure. Its appearance in mag 
trifled thin sections under both ordinary and polarized light is very well shown ii 
PI. XXXIX, part 3, Nineteenth Annual Report United States Geological Survey : 
which would answer almost equally well for many of the Pennsylvania "soft vein' 1 
slates. 
The following analysis (specimen P = D. XIV, '95, 305d) of black slate from th 
abandoned quarry, one-fourth mile east of Benson Village, Rutland County, Vt., wa 
also made by Dr. W. F. Hillebrand: 
«See footnote <>,. page - * « i on pyrite and marcasite. 
