WALCOTT.] VIRGINIA. 135 



It will be noticed that Prof. Rogers adopts the same reference for the 

 ferriferous or iron-bearing slates and shales that his brother did for the 

 supposed equivalent formation in Pennsylvania. 



Prof. J. L. Campbell published two papers in 1879, 1 in which the 

 Primal series of Prof. Rogers is described. These were followed in 1880 

 by a revised description of the Silurian formation in central Virginia. 2 

 His observations will be noticed in the section on the Cambrian rocks 

 of Virginia. In another paper he gives a definition of the " Primordial" 

 as follows : 



The Primordial. — The great bed of ferriferous shales and sandstones skirting the 

 western base of the Blue Ridge from Tennessee to the Potomac ; in the upper part of 

 formation No. I of Prof. Rogers's Appalachian series. 3 



The most complete and detailed description of the formations re- 

 ferred to the Primal series of Rogers is that of Prof. W. M. Fontaine, 

 published in 1883. 4 The section is formed of conglomerate at the base, 

 subjacent to shales, upon which the so-called Potsdam quartzite rests. 

 The upper member of the Primal series is the ferriferous shales. The 

 entire thickness of this section is given as 2,380 feet, and the data 

 given by Prof. Fontaine will be used largely in the summing up of our 

 knowledge of the Primal series in Virginia. The reader is referred to 

 that section for further details. 



In an article upon the iron ores of the valley of Virginia, Mr. Andrew 

 McCreath divides the u Primal or Potsdam sandstone" (Primal or Pots- 

 dam formation) into (1) lower slates, (2) sandstone, (3) upper slate. 



First. In the lower slates, or those geologically underneath the Potsdam sandstone 

 oeciirs a red hemitite ore, sometimes in beds of considerable thickness and of good 

 quality. This is the so-called " specular ore " of the Blue Ridge, and it has been quite 

 extensively developed at numerous points, notably in Botetourt and Bedford Coun- 

 ties. * * * Second. In the Potsdam sandstone itself, important beds of iron-ore 

 have been observed. The ore is generally a close-grained, brittle, dark brown hem- 

 atite, invariably cold-short. In Rockbridge County a bed of it fully ten feet thick is 

 exposed for a considerable distance on the Vesuvius property. * * * Third. The 

 upper slates, however, are by far the most important from an economical standpoint, 

 forming, as they do, one of the richest repositories of brown hematite iron ore in 

 Virginia. They intervene between the Potsdam sandstone and the base of the cal- 

 ciferous limestone, and they are found all along the western slope of the Blue Ridge — 

 being geologically coextensive with it. They are generally more or less disintegrated, 

 or decomposed into variegated clays ; and while they may not always carry a contin- 

 uous ore bed, yet, wherever the formation exists, deposits of iron ore of greater or 

 less extent may be confidently looked for. 6 



1 Silurian formation in central Virginia. Am. Jour. Sci., 3d ser., vol. 18, 1879, pp. 16-29. Geology of 

 Virginia; Balcony Falls ; The Blue Ridge and its geological connections. Some theoretical consider- 

 ations. Ibid., pp. 435-445. 



'The Silurian formation in central Virginia (revised). The Virginias, vol. 1, 1880, pp. 41-45,54-56. 



8 The mineral resources and advantages of the country adjacent to the James river and Kanawha 

 Canal and the Buchanan and Clifton Forge Railway. The Virginias, vol. I, 1880, p. 3. 



4 Notes on the mineral deposits at certain localities on the western part of the Blue Ridge. The 

 Virginias, vol. 4, 1883, pp. 21, 22, 42-44 



* The iron ores of the valley of Virginia. Am. Inst. Mining, Eug., Trans., vol. 12, 1884, pp. 18-20. 



