116 SLATE DEPOSITS AND INDUSTRY OF UNITED STATES. 
miles north-northeast of Snowden station, where Rocky Row Run enters the James 
River, and about 1,200 feet above it. About 250 feet of slate are exposed with a 
bedding strike of N. 05° £., forming a fiat-topped anticline, whose northern limb 
dips 35° at the surface, but becomes vertical at the bottom of the quarry, and for a 
space of a few feet dips steeply south, indicating a possible overturn structure. The 
cleavage strikes N. 45° E., dips. southeast at 32°. The bedding forms finely plicated 
ribbons of quartz and calcite several inches wide on the cleavage surfaces. Joints 
strike N. 18° E., dip 70° W., also N. 18° W., dip 65° E. The grain makes an angle 
of from 90° to 101° with the bedding and is said to be very marked. 
This slate is very dark gray, to the unaided eye has a minutely granular texture, a 
moderately smooth cleavage surface, with very little luster. It is not graphitic, 
Scale of miles 
Contour interval 100 feet 
Fig. L3.— Map showing.location of Snowden quarries, A.mhers1 County, Va. Quarries shown by crossed 
hammers; slate prospects by round dots; strike of commercial slate by arrows. 
shows no pyrite on sawn edge, lias no magnetite, duos not effervesce with cold dilute 
hydrochloric acid, is quite sonorous, has a very slight argillaceous odor and is said 
not to fade. 
Under the microscope it shows a matrix of muscovite (sericite), with aggregate 
polarization not very brilliant owing partly to the coarseness of many of the other 
constituents. Quartz fragments measure up to 0.08 mm.; chlorite scales and lenses 
up to 0.28 in length, rarely 0.42 by 0.2 mm., numbering about <> per square milli- 
meter; also muscovite scales up to 0.09 mm.; some carbonate, but in exceedingly 
minute rhombs and plates; grayish carbonaceous (?) matter; about 55 spherules and 
pyritohedrons of pyrite per square millimeter, measuring up to 0.005 mm.; abundant 
rutile needles, ami occasional fragments of zircon. 
The chief constituents of this slate, arranged in descending order of abundance, 
