474 H. D, Campbell—The Potsdam Group, Virginia. 
rectangular masses. This variety of ore in Virginia seems to 
be characteristic of the Potsdam formation. OCresting the 
ridge on the left, in ascending Matt’s Creek near its source is 
found a white sandstone of firm texture containing Scolithus 
borings. It has a dip of 45° S.E. which carries it across the 
head of Snow Creek to the crest of Piny Ridge which is not so- 
elevated. 
If we cross James River and follow the eastern face of the 
Blue Ridge toward the N.H. for several miles we find sand- 
stones carrying Scolithus markings and beds of slate alternat- 
ing with them, all dipping S.E. They correspond very closely 
in character and position with those described to the south of 
the river. Three miles N.E. of Rope Ferry a bed of these 
slates is quarried by the Virginia Slate Mining Co. for roofing 
purposes. ey are somewhat different lithologically from 
the corresponding slates along the western slope of the Blue 
Ridge, being much more highly metamorphosed and _ hence 
having a more perfect cleavage. 
The foregoing observations led to the conclusion that the 
_ stratified rocks upon the western and eastern slopes of the 
Blue Ridge belong to the same geological formation, and that 
_ the latter ought to be classed as Potsdam or Lower Cambrian 
instead of Archean. This would make of the Blue Ridge an 
immense broken arch at Balcony Falls. 
This broken arch or anticline is immediately succeeded by 
an unbroken syncline about two miles in width, near the axis 
of which is Rope Ferry Bridge. How far on either side of the 
river this syncline may extend we have not yet fully deter- 
mined. The upper beds of sandstones and slates do not make 
their appearance for some distance on either side of the river, 
having probably been somewhat broken in their upheaval, an 
washed away before the river became confined to its present 
narrow channel. 
y 
east of the Blue Ridge at Balcony Falls belongs to the Lower 
Cambrian or Potsdam group of rocks, and that the Primordi 
beach of the Palwozoic Sea was farther east at this locality 
than was formerly supposed. 
Washington and Lee University, Lexington, Va. 
