424 W. M. Fontaine—Primordial Strata of Virginia. 
from six to ten feet. This seam is the decayed outcrop of an 
argillaceous layer highly charged with pyrites, for at the depth 
of forty feet the ore is cut off by pyrites. This, and the other 
features of the rock, indicate that the entire mass of limestone 
has been metamorphosed by the action of water holding min- 
eral matters in solution. 
To the west of this limestone the usual formation of varie- 
gated shales occurs. The thickness of the limestone seen was 
about ninety feet. 
e section at Harper’s Ferry thus indicates an increase in 
the proportion of fine material over that shown to the south- 
est development in Tennessee. 
I have given the above sections in greater detail than I 
would have otherwise done, from the fact that Prof. Wm. 
B. Rogers, in his Virginia reports, does not (with the exception 
of the strata at Balcony Falls) give detailed descriptions of the 
individual members, and the order of succession of the lowest 
Primordial strata, the nature of his report forbidding such de- 
tails. With the single exception of the Scolithus, there are no 
fossils to be seen in these lower rocks which can indicate their 
age. It will be seen from the above notes that in Virginia we 
have below the Calciferous limestones a great development of 
sandstones, shales and conglomerates, which attain in the mid- 
dle portion of the State a thickness of over 2,000 feet, and 
increase in the proportion of coarse materials to the southwest. 
They probably attain greater thickness in that quarter, while 
to the northeast the amount of sediment diminishes, and the pro- 
portion of fine matter increases. This change is plainly due to 
the increasing development to the southwest of the syenitic rocks 
which formed the shores of the ancient seas, and to the greater 
violence in that direction of disturbing forces. The Potsdam 
sandstone forms one of the upper members of this group. 
Much further study of these strata is required to settle the 
question whether the entire series is a great expansion of the 
otsdam, or whether divisions may be made corresponding to 
other epochs. The fact that at Rockfish oe and to the south- 
west, a great body of ferruginous slaty shales separates the 
lower, highly siliceous and altered, sandstones from the upper 
kaolin sandstones of probable Potsdam age, seems to indicate a 
change in the conditions of sedimentation sufficient to justify 
such a division, in which the Acadian strata may be found. 
