VIRGINIA AND WEST VIRGINIA. 



181 



more purely Calcareous and Argillo-Calcareous strata appertaining to the base of the Siluro-Cam- 

 brian, Trenton or Matinal group. The frequent faults, inversions and repetitions of the beds in 

 the great valley, and the rarity of fossils in the Auroral rocks, have interfered with a precise 

 demarcation of formations; but there can be little doubt, from fossil and other evidence, that they 

 cover the period of the formations 3 a., 3 b., 3 c., assigned to them in the Table. Hence, and as 

 indicating the formations near as well as at the localities, the designation 3 a. b. will be used for 

 these rocks up to the top of the magnesian, without distinguishing between Calciferous and 

 Quebec (or Levis), and 3 b. c., for the remaining strata up to the well defined base of the Siluro- 

 Carnbrian, Trenton or Matinal group, 4 a. b. and c. 



5. The Potsdam, or Primal group, includes in Virginia, where complete, besides the Potsdam 

 proper, the ferriferous shales next above, and the slates, shaly grits and conglomerates, below this 

 formation. It is exposed in varying mass and completeness on the western slope and in the west 

 flanking hills of the Blue Ridge throughout much of its length, often, by inversion, dipping to the 

 southeast, in seeming conformity beneath the older rocks of the Blue Ridge, but often, also resting 

 uncomformably upon or against them. These older rocks, comprising masses referable probably 

 to Huronian and Laurentian age, include also a group of highly altered beds, corresponding ap- 

 parently to the copper-bearing or Keweeuiau series of northern Michigan, and perhaps to the lately 

 described Dimetian rocks of Wales. 



6. The letters A, B, C, D mark four rather distinct groups of Archaean rocks found in Virginia, 

 of which the first three may probably be referred to the Laurentian, Huronian and Montalban 

 periods respectively, and the fourth to an intermediate stage the Norian or Upper Laurentian. 



7. This belt of Siluro-Cambrian slates extends continuously from the Potomac River, to a point 

 about ten miles south of Staunton, a distance of 140 miles, beyond which it becomes narrow and 

 discontinuous. In the tract corresponding to the interval, from Strasburg to Harrisonburg, it 

 encloses the complex synclinal of the Massanutten Mountains, consisting of massive ranges of 

 Silurian rocks 5 a., 5 b., with some bands of 7 and a few traces of Devonian 10 a., all resting in the 

 wide undulated trough of the slates. From Strasburg southwest, the railroad keeps generally a 

 distance of from one half to one mile west of the edge of the slates, but sometimes impinges upon 

 it, affording ready access to fossiliferous beds of 4 a., b. and c. 



8. About 13 miles west-by-north from this are the Rawley Springs, and a few miles farther the 

 remarkable fissured rocks known as Moravian Town, both in Ponent 12. West-by-south, about 20 

 miles, are the Dora coal mines, in Vespertine 13 a., of Narrowback Mountain anthracite, faulted 

 and crushed, The irregular fault which, with many interruptions, extends from near the Potomac 

 River along the northwest edge of the Great Valley in the line of the Little North Mountain for 

 about 120 miles, is seen near these localities to bring the Siluro-Cambrian 4. of the valley into 

 juxtaposition with the Devonian 10. to 12. 



9. About eight miles east of this are Weyer's and Madison's caves, situated in a ridge of steep 

 dipping limestone, 3 a. b , near the South River. 



10. In this part of the gold belt are situated the old workings known as Tinder's, Boxley's, 

 Baker's, Triple Fork and Walton's Mines. 



11. This is a good point of departure for examining the rock structure of Panther Gap, 5 a. b., 

 mostly inverted, and the wild passage of the North River through the same formations at Streck- 

 ler's Gap, " The Goshen Pass." About 10 miles southwest are the Rockbridge Alum Springs, in 

 10 a. b. 



12. About three miles north of this, on the Cow Pasture River, is the Blowing Cave of Bath 

 County, in an anticlinal of 8. Oriskany; and twelve miles farther north-by-west, near the same 

 river, is the noted intermitting stream called the Ebbing Spring, in a ridge of 7 and 8, on east side 

 of Tower Hill, east of Warm Spring Axis. 12 milea southwest to Bath Alum Springs, in 10 a., and 

 thence 5 miles to Warm Springs, 3 c^4 a. 



13. Where traversed by the Jackson's River, this anticlinal shows itself as a great arch built 

 up of the successive concentric beds of 5 a. b. c., and flanked by 7. and 8., followed by 10 a., and 

 having a span, as measured by the highest sandstone bed, of about 3,300 feet. The main arch, 5 a. 

 Levant, or Medina, white sandstone, is regular and unbroken, but the outer concentric belts, made 

 up of the hard members of 5 b. c., are distorted and in part inverted on the west side of the axis, 

 where by a slight fault the beds of 7. pass suddenly from a nearly vertical to a horizontal position. 

 Towards the southwest, this axis opens, to form the Rich Patch Valley, bringing to view the 

 Siluro-Cambrian 4 a, b, c, and still farther southwest becomes the closed anticlinal known as the 

 Pott's Creek Mountain. Heavy beds of iron ore (Hematite) have been opened on both sides of 

 this axis, as at Roaring Run, Callie's, Low Moor, and Kayser's near Clifton Forge, associated wfth 

 formation 8. Oriskany. ^ The fossil ore of 5 b. is also mined at several points. 



