VIRGINIA. H3 
few inches to 12 feet in thickness (plagioclase, olivine, magnetite, augite), weather- 
ing in conchoidal masses with a yellowish-brown surface. The formation is bounded 
on the east by the quartzite cut by the James River. If this quartzite be a west- 
wardly overturned syncline, it would overlie the slate; if an anticline of like character, 
it would underlie the slate, in either case in apparent conformity. ( >n the wesl of the 
formation at Virginia Mills there are chloritic, sericitic, quartzose, and feldspathic 
schists striking N. 25° E. and dipping 90°, crossed diagonally by a small basaltic dike, 
also certain bright-red weathering chloritic, quartzose, and feldspathic schists, possibly 
the same as the above, but both of uncertain age. 
The commercial slate itself appears to occupy a belt two-fifths of a mile wide along 
Hunts Creek, which is a southern tributary of Slate River. At Arvonia its course is 
N. 35° E., roughly like that of Hunts Greek, which meanders through it; but on the 
north side of the James, 3 J miles north-northeast of Arvonia, the strike of the slate 
is N. 20° E., like that of the quartzite at Bremo Bluff. There appears thus to be a 
bend in the slate beds between Arvonia and the north side of the James. The dis- 
covery of certain crinoids and more recently of brachiopods, trilobites, etc., in the 
quarried slate at Arvonia shows it to be of Ordovician age." Mr. E. 0. Ulrich, to 
whom recent collections of these fossils were referred, determine- them as unques- 
tionably of Upper Ordovician age, but he finds that the fossils are of such strange 
types that it will require a very critical study to determine whether the beds are to 
be correlated with the Mohawkian or with the Cincinnatian formations. The dikes 
are probably of Mesozoic age. 
Ai vonia. — The quarries near Arvonia are scattered along the sides of Hunts Creek 
for a mile northeast of that place. The principal quarries in operation in May, 1904, 
were the "Old or Big" quarry and the "Middle" quarry of the John R. Williams 
Slate Company, and the Fontaine quarry of A. L. Pitts. Several others were just 
being opened or were temporarily abandoned. 
The "Big quarry" measures 300 feet along the cleavage, 200 across it, and 125 in 
depth. Bedding and cleavage are identical, striking X. 37° E., dipping 80° SE. 
There are vertical dip joints striking about northwest, strike joints northeast, south- 
west, dipping 75°-80° SE., also two sets of diagonal joints, one dipping 30° E. and 
the other 55° W. The latter system has a "post" 5 feet thick full of shear zones. 
There are also gently undulating "flat joints," to which the grain is parallel. Quartz 
veins in this quarry contain calcite, chlorite, and biotite. 
The "Middle quarry" of the same firm is 500 feet along the cleavage, 350 feet 
across, and in places 350 feet deep. Bedding and cleavage strike N. 33° E., dip 85° 
SE., and are crossed by northwesterly vertical joints. At the south end is a vertical 
dike of olivine basalt, 12 feet thick, traversing the slate diagonally, with joints parallel 
bo it on both sides and, for a few feet on its north side, with horizontal joints from 4 
to 6 inches apart. The quality of the slate is said to be better a little beyond the zone 
Df these joints than it is at a greater distance from the dike. A horizontal joint in 
;his quarry meanders as much as 10 feet from the horizontal in a distance of 50 feet. 
The slate from the Williams quarries is a very dark gray, with a slightly greenish 
lue. To the unaided eye it has a minutely granular crystalline texture and a slightly 
■oughish, but very lustrous, surface. It is slightly graphitic and magnetitic, shows 
jyrite on the sawn edge, does not effervesce in cold dilute hydrochloric acid, and is 
/ery sonorous. 
Under the microscope it shows a matrix of minute alternating beds, chiefly of fine 
nuscovite, with coarser ones, chiefly of quartz, the former with a brilliant aggregate 
.polarization, the latter with a faint one. These beds are parallel to the cleavage. 
Ji?he quartz fragments measure up to 0.085 mm. Scattered throughout both the 
■ «See Darton, N. H., Fossils in the "Archean" rocks of central Piedmont, Virginia: Am. Jour. Sci., 
id ser., vol. 44, 1892, pp. 50-52. 
