362 W. M. Fontaine— Primordial Strata of Virginia. 
ciferous epoch. These strata are well exposed along the west 
base of the Blue Ridge throughout the State. 
The careful and accurate studies of these and the overlying 
formations, made by Prof. Wm. B. Rogers, have thrown much 
light on the complicated stratigraphy of the region. He 
shows that in the northern portion of the State, extending 
from Harper’s Ferry to the south end of Page County, the 
Primordial slates are inverted so as to overlie the later forma- 
tions on the west, and to pass with a high southeast dip under 
the like dipping strata of the Blue Ridge. In the middle coun- 
ties, especially near Balcony Falls, these strata lie with a gentle 
northwest dip on the west slopes of the Blue Ridge. In some 
of the more northerly portions of this district, they lie immedi- 
ately on the edges of the southeast dipping older slates, while 
at Balcony Falls and its vicinity the two systems of strata are 
separated by a ridge of syenitic rocks. Farther to the southwest 
inversion again occurs. This inverted dip is found in all the 
strata of Silurian age and extends into those of the Devonian. 
The former occupy nearly all of the “ Great Valley of Virginia,” 
while the latter appear in the Great North Mountain, and its 
prolongations, which bound this valley on the west. The strata 
of the valley lie generally in a closed synclinal, producing a 
continued series of southeast dips. This compressed mass of 
rocks, on the west side of the valley, is thrust up against, and 
partly over, the Devonian strata, affecting them also with a 
southeast dip, producing a long line of fault, and bringing 
Hudson River shales up so as to overlie even strata of the 
Subcarboniferous period. 
It will thus be seen that the amount of displacement pro- 
duced is enormous. Owing to the contortions thus caused, and 
the possibility of repetitions from closed folds, all estimates of 
thickness, unless based upon long-continued examinations, 
must be received with caution. 
I shall in this paper commence with the description of the 
section obtained at Balcony Falls. This I do because the 
strata there appear to present their normal development and 
dip; and also for the reason that here alone has Prof. Rogers 
given, in any detail, a description of the Primordial strata. It 
will be seen that my results do not agree entirely with his, and 
I must confess that I cannot reconcile them. In view of this 
difference, I should hesitate to maintain the correctness of my 
observations were it not that they are substantially verified by 
the section made at Rockfish Gap. This last was made along 
the cuttings for the railroad at that point, which were not in 
existence when Prof. Rogers made his examinations. 
Before giving my own results at Balcony Falls, I will quote 
f. Rogers’s description of the strata there found. He says: 
