470 H. D. Campbell—The Potsdam Group, Virginia. 
Art. LXI.—The Potsdam Group East of the Blue Ridge at 
Balcony Falls, Virginia ;* by H. D. CAMPBELL. 
Batcony Fatis is the name given to a succession of rapids 
in the gorge through the Blue Ridge by which the James River 
finds its way from the valley to Piedmont, Virginia. There 
is no other locality in Virginia where the Potsdam formation 
is better exposed than at this point. All of its strata are cut 
through by the river. The accompanying map and section 
are designed to throw a clearer light upon the topography and 
geological structure of the region.. : 
The Blue Ridge has been here sculptured into seven ridges, 
the middle one of which is the most clearly defined and alone 
has a granite axis. This isthe Blue Ridge proper. On the map 
it is called Rocky Row on account of a very bold escarpment 
of sandstone upon its southeast face. The three ridges lying 
northwest of it are each crested with sandstone, and have been 
formed by the disintegration and washing away of the inter- 
yening slates. As seen from the river they appear as peaks 
with depressions between them, The ridges lying southeast of 
Rocky Row run rather obliquely across the beds of sand- 
erosive power of streams several miles in length, such as Matt’s 
Creek and Snow Creek. 
Geology.—The section is meant to be somewhat general, and 
hence the local displacements are left out, which makes the 
strata appear thicker than they are in reality. It represents 
an immense broken arch, or anticline, of Potsdam sandstones 
and slates, followed to the southeast by a trough or syneline of 
For about a mile after entering the gorge through the moun- 
tains the James River runs almost at right angles to the strike 
of the strata. Here and there it has washed away the softer 
slates and caused local displacements of the sandstones on either 
side, its waters having for a long time been dammed back by 
the lowest heavy bed of Potsdam sandstone, which is very arn 
pailt 
passing Balcony Rock the river runs obliquely across i 
strike. By its erosive power, aided by a fissure, and probably 
by ice also, it has worn its channel deep into the underlying 
* A short paper upon this subject appeared in this Journal, Sept.,1884. 
