Campbell — Roger is Geology of the Virginias. 367 



nearly vertical with a high dip to the S.E., and in width ex- 

 tend half a mile " (p. 313). 



The foregoing would serve well as an accurate description of 

 the lower beds of Cambrian age at several points we have ob- 

 served along the Blue Ridge, with perhaps the exception of the 

 amygdaloidal greenstone ; but these beds, at least those on the 

 east side of the mountain, are nowhere in the Reports referred 

 to his formation I. Though on section No. 9, accompanying 

 the published volume, we are pleased to find our suspicions 

 verified, so far as the coloring of the section indicates Prof. 

 Rogers's conclusions — arrived at no doubt from his latest re- 

 vision of his earlier work. There is at least a probability of 

 other portions of the eastern margin of the Cambrian rocks be- 

 ing cut off from their main mass by the elevation of the core 

 of the Blue Ridge. At any rate, enough has been definitely 

 determined to prove that the axis of this mountain does not 

 everywhere mark out the eastern coast line of the great Paleozoic 

 ocean, and that it will be worth our while to search for shore 

 marks farther east than has been our custom heretofore. 



Points convenient for studying the Cambrian group in Vir- 

 ginia have been incidentally mentioned already, and nothing 

 more is called for under this head than a summing up of such 

 localities as are readily accessible from railway stations. At 

 Harper's Ferry, Prof. Rogers's section No. I appears to make the 

 main mountain and the Short Hill some distance east of it, 

 both Cambrian, with an uplift of Archaaan beds between 

 them. In his notes in Macfarlane's Guide he calls the rocks 

 here, " Altered Cambrian 2b, or Archaean B, followed west by 

 Cambrian 2b, 3a." Prof. Fontaine, in his notes for Macfarlane 

 on the Baltimore & Ohio railroad, says : " The gorge at Har- 

 per's Ferry is cut through metamorphic rocks, of probably 

 Huronian age. One-and-a-half miles west of the station, a fault 

 brings down the Potsdam and Calciferous rocks against the 

 Azoic." This is an interesting point, and worthy of further in- 

 vestigation. It seems to present another example of a belt of 

 Cambrian rocks thrown to the eastern side of the Blue Ridge 

 axis. We have not studied this portion of the formation with 

 sufficient care to form a definite opinion of its peculiarities of 

 structure. 



The Manassas Gap railroad cuts the beds of this age between 

 Happy Creek and Front Royal. The same formation is again 

 well exposed at Thornton's Gap, a few miles east of Luray on 

 the Shenandoah Valley railroad. There are numerous points 

 on the same line from which good exposures of 2a, b, may be 

 conveniently reached, as the road skirts the margin of the 

 formation from Front Royal to Roanoke, a distance of 177 

 miles. Such points as Milnes, Crimora (near Turk's Gap), 



