W. M. Fontaine— Primordial Strata of Virginia, 867 
was induced by this peculiarity to study closely its compo- 
sition, under the impression that such was its nature. 
These conglomerates crop out on the top of the mountain, 
and are partially exposed in the road. Here I discovered that 
the upper part of No. (4) was composed of a mass of angular 
fragments of slate cemented together by conglomeritic matter. 
These fragments of slate, sometimes as large as the hand, are of 
precisely the same character as the argillites which make up so 
large a part of the Blue Ridge, especially to the north. Their 
existence here shows not only that these argillites are older than 
the lowest Primordial rocks, but that they were already in a 
metamorphosed condition prior to the Primordial Period. The 
shales lying between the beds of conglomerate are very much 
contorted, and they, with the succeeding strata up to (8), seem 
to be mainly composed of finely comminuted feldspathic and 
argillaceous material, which had not been long exposed to 
ecomposing and dissolving agencies. 
The massive beds numbered (8) in the section differ strik- 
ingly from the underlying rocks in every respect. The material 
composing them is almost entirely quartz and of a white color, 
the grains being more or less rounded and cemented together. 
A few specks of yellow earthy matter occur, marking the posi- 
tion of decomposed particles of feldspar. With this exception, ~ 
the rock is remarkably free from all minerals except quartz. 
If I mistake not, this is the rock mentioned by Prof. Rogers as 
typical No. 1, or Potsdam. But from his descriptions, given 
elsewhere in his reports, the strata which I have numbered (10) 
coincide more nearly with his sandstone, No. is also 
agrees best with the relative positions of No. (10), and of the 
Calciferous sandrock, which forms the upper part of No. (11 
to give details. I may state, however, that the sandstones 
which occur in the shales of this series are quite thin. The 
coarsest and most massive layers are not more than 8 or 10 
feet thick. It is worthy of note that these sandstones are much 
more altered than the shales by the disturbances to which cs 
have been subjected. The shales seem hardly at all affected, 
while the sandstones are much indurated and often impregnate 
with epidotie and other metamorphic products. The material 
composing the shales is gray, argillaceous matter, with some 
eds of brown and reddish colors. 
No. (10). This series, which is — the equivalent of the 
Potsdam sandstone of New York, is composed of alternating 
Strata of quartzite and kaolin shales. The quartzite layers vary 
in thickness from 20 feet to 3 or 4 feet. Many are quite compact, 
and some resemble vein quartz in fracture and other features. 
