HT, D, Campbell—The Potsdam Group, Virginia. 473 
slope. In Macfarlane’s Railway Guide (1879, p. 182) we find 
the following note by Professor Rogers: ‘* About twenty miles 
northwest of this point (Lynchburg) by canal or road, we enter 
the gorge by which the James River traverses the Blue Ridge, 
where are exposed fine sections of Archean rocks, A and B, 
and of the Cambrian, Primal 2a, resting unconformably on 
the western slope of the former, and occupying the flanking 
ridges which adjoin the valley.” 
It is with diffidence that I offer my views as opposed to 
these, making (as seen in the section) an anticline here instead 
of unconformability ; and yet I feel confident that the highly 
metamorphosed condition of all the rocks east of the Archzan 
axis, and the hurried review of this locality, led these geolo- 
gists to place these sandstones and slates as Archeean, and that 
if the facts which I shall present had been known our views 
would coincide. 
The evidences in support of the section I have drawn are as 
follows. Rocky Row on the north side of the river is capped 
with a hard sandstone of a grayish color dipping gently toward 
the northwest. Grassy Island Ridge, on the south side of the 
river, is capped with a sandstone of similar appearance, though 
not so thick, dipping about 40°S.E. Each o beds of 
sandstone is underlaid by a brownish decomposing slate, and a 
bed of coarse conglomerate which lies upon the Archzan 
rocks, To the N.E. of the river about four miles and again 
to the S.W. about one mile these strata seem to connect and 
make a complete anticline. But this might seem to be the 
case where there is unconformability and hence we need stronger 
proof. 
In all of the heavy beds of sandstone in the Potsdam group 
of the Blue Ridge above the lowest, Scolithus borings are 
found, varying in abundance in different localities, and being 
always more numerous in the higher beds. These markings 
have determined the age of the rocks along the western slope, 
together with their stratigraphical position. They occur here 
only in the upper beds, No. 8; but at White’s Gap some miles 
sandstone. Going now east of the axis of the Blue Ridge and 
examining the sandstones along the ridge between Matt’s 
Creek and Snow Creek we find unmistakable Scolithus borings. 
These sandstones are conformable with that on Grassy Island 
Ridge. Proceeding up Matt’s Creek we cross two of these 
beds, each carrying Scolithus borings. Between them lie 
heavy beds of slate, and in the first of these is found a bed of 
hematite ore similar to that mentioned above as occurring on 
the western side of the Blue Ridge and locally known as 
“block ore” on account of breaking readily into cubical and 
Am. Jour. Sct.—Turrp Series, Vou. XXIX, No. 174,—JuUNE, 1885. 
32 
