VERMONT. 
<n 
ing the cleavage, channeling in a horizontal direction becomes necessary. Ii is, 
therefore, easier to obtain very large slabs tor mill stock than small ones for roofing 
slates. 
The slate is very dark gray; to the unaided eye lias a very fine texture. The 
cleavage surface is very smooth and very lustrous, but lias hen- and there minute 
longish. crystals of pyrite pointing in the direction of the -rain, also some very minute 
nonmetallic lenses. It appears to be slightly graphitic and contains a very little 
magnetite. The sawn edge shows lenses and crystals of pyrite from 1 to 3 mm. Ion-. 
There is no effervescence in cold dilute hydrochloric acid. It is very sonorous, very 
fissile, and does not discolor. 
Fig. 11.— Syncline at Vermont Black Slate Company's quarry, near 
Northfield, Vt.; looking S. 12° W. Depth of syncline as figured, II 
feet. 
Under the microscope shows a matrix" of muscovile (sericite), with a very brilliant 
aggregate polarization and a very even texture. There are abundant quartz frag- 
ments up to 0.06 mm., exceptionally 0.1 by 0.03 mm. The lenses and crystals of pyrite 
(including a small percentage of magnetite) number from 7 to 8 per square millime- 
ter and measure from 0.05 by 0.03 up to 0.06 by 0.1 mm. These figures, however, do 
not include the exceptionally large ones, visible without a glass. The long axes of 
these lenses and crystals lie in the cleavage but parallel to the grain. They are 
usually surrounded by a rim of secondary quartz and muscovite, sometimes also 
of chlorite, radiating from the nucleus a distance of 0.04 to 0.0S mm. In some cases 
"See Glossary. \>. 1 I''.. 
