366 Campbell — Rogers's Geology of the Virginias. 



the former, theD a repetition of the sandstone, again a slate, 

 and at the termination of the gap heavy beds of massive 

 white sandstone, such as constitute the type of this forma- 

 tion. The average dip of the latter, as presented in the impos- 

 ing cliffs which guard the entrance to the pass, is 55° N.W." 

 (p. 205). The above account given by Prof. Rogers does not 

 coincide entirely with the geology of this same mountain gorge, 

 as presented in a paper published in this Journal, vol. xxix, 

 June, 1885. The difference however, so far as regards the por- 

 tion west of the axis of the Blue Ridge, is not in the general feat- 

 ures but simply in the more detailed account given in the Journal. 

 But as to what is east of the axis the case is quite different. We 

 have fully ascertained as a settled fact that the beds of sand- 

 stones, conglomerates and slates for fully two miles east of the 

 main mountain are of Cambrian age, forming a comparatively 

 shallow synciine resting on Archaean rocks which are exposed 

 along both of its margins, as shown in the paper referred to 

 above. We have recently ascertained that this area cut off 

 from the principal mass of the Cambrian beds, and thrown over 

 to the eastern base of the mountain, extends at least ten miles 

 northeast of James river towards the head waters of Pedlar 

 river in Amherst county. 



Some months before this volume of Rogers's Reports came 

 into our hands, we examined another area on the east side of 

 Blue Ridge at Tye River Gap in Nelson county, which is cov- 

 ered with alternating beds of conglomerates, slates and sand- 

 stones, considerably metamorphosed but bearing a striking re- 

 semblance to the lower Cambrian beds east of the mountain at 

 Balcony Falls, which we suspected were of the same age. The 

 only circumstance militating against that conclusion, was the 

 absence of Scolithus borings in the sandstones. But this may 

 be accounted for by the fact that these remains are rarely if ever 

 found in the lowest beds in this region, and the additional fact 

 that higher beds seem to have been swept away. More ex- 

 tended and minute research in this region may, however, yet 

 prove the presence of Scolithus borings. In describing a sec- 

 tion of rocks cropping out at Tye river Gap, Prof. Rogers says : 

 " There are also noticed two bands of sandstone and slate. That 

 on the western side occurs about one mile below the summit, 

 is about 200 yards in width, and consists of gray and red- 

 dish slates, sometimes micaceous, with associated layers of 

 sandstone, conglomerate, greenstone and greenstone slate. The 

 greenstone is sometimes amygdaloidal. 



These layers are horizontal, and with a moderate dip to the 

 S.E. The other band occurs about •§ mile below the summit 

 on the east side, and presents repeated alternations of red and 

 gray slates, white sandstones and conglomerates. They are 



