MMARY VIRGINIA. 291 



thence to the - meat of tbe Valley limestone. 1 At some later 



date, however, be die nail outcrop of the Primal serif- 



the eastern dope of the Blue Ridge, in Rockbridge County, and drew 

 it in on section 9 of the plates of sections published in connection with 

 "The Virginias" in 1884. The Primal sandstones and shales are rep- 

 resented as occupying a narrow, deep basin on the eastern slope of the 

 Archean rocks of the Blue Ridge. In this beautiful series of illustra- 

 tions the twenty sections crossing the Primal series at subequal dis- 

 tances from the Potomac River to the Tennessee line illustrate very 

 fully Prof. Rogers's interpretation of the geological structure, charac- 

 ter, and thickness of strata forming ih3 Primal series. 



Prof. W. M. Fontaine in 1875 supplemented the work of Prof. Rogers 

 "by a detailed description of the sections of the " Primordial n strata at 

 Balcony Falls in Rockbridge County, Rockfish Gap in Augusta County, 

 and at Barpert Ferry on the Potomac. He concludes that the entire 

 thickness of the Primordial strata at Harper's Ferry can not be much 

 over 1,000 feet, and that they are composed of slaty rocks, similar to 

 the variety of the lowest slate seen at Rockfish Gap, and a sandstone 

 which much resembles some of the quartzites of the lower strata of the 

 same locality. The section differs from that of Rockfish Gap and Bal- 

 cony Falls in the absence of the coarser materials and the succession 

 of shales and sandstones, with the subjacent conglomerate that rest on 

 the Archean. The lower argillites, forming the main portion of the 

 rid^e and which Prof. Rogers included in his Primal series in section 

 2s o. 2 accompanying ;: The Virginias," Prof. Fontaine refers to the 

 Archean ; whether of Laurentian or Hnronian age, he does not under- 

 take to decide. 2 



At the second annual meeting of the Geological Society of America, 

 at Washington. D. C, December 31, 1890, a paper was read by Met 

 H. R. Geiger and Arthur Keith on the structure of the Blue Ridge 

 near Harper's Ferry. 



Several sections, taken on both the north and south sides of the 

 Potomac River, show that the geologic succession at the base 

 limestone upon which rests a series of shales, subjacent to a quartzite 

 which corresponds to the Medina sandstone of the sections farther to 

 the north and south. This section is the one described by Prof. Rogers 

 as an overturned section, the quartzite corresponding to the primal 

 quartzite of the Pennsylvania section, its present position being 

 accounted for by the complete overturning, thus reversing the section. 

 The authors of the paper mentioned conclude that the succession 

 normal one from the pre-Paleozoic rocks through the limestone and 



i «»nd report of the progress of the gelogical survey of the State of Virginia for the year 1837. 

 Richmond, l-.^, pp. 14, 15. 



• f the Virginia.-*, 1884, pp. 167-169. 

 li.rpoit of the progress of the geological survey of Virginia for 1838 ( Richmond, 1639) pp. 6, 9-1A 

 Geology of tho Virginia- •». 197, 198, 203-209. 



•On the Primordial strata of Virginia. Am. Jour. Sci, 3d ser., vol. 9, 1875, f 



