196 J. L. and H. D. Campbell — Wm. B. Rogers's 



eroded by mountain streams, the beds of limestone are com- 

 monly denuded, and the two formations may be seen in close 

 contact. The very intimate relations thus shown between 

 these two formations, and the abrupt transition to the next 

 higher group incline us, as already stated, to regard them both 

 as belonging to the same general geological age. 



Tlie Corniferous Group of Devonian age (9a, b, c), as far as 

 our observations have extended, and as far as we can draw any 

 inference on that point from Rogers's Reports, has no well- 

 defined representative in the Virginia portion of the Appa- 

 lachians, we therefore pass to the next higher series, on which 

 we wish to make a few remarks. 



No. VIII, R. (equivalent to 10a, b. c, and 11a, b, Dana), con- 

 sists of a remarkable series of slates that are found crowded 

 into folds and crumpled masses in the synclines between the 

 sandstone ridges of 5a, b. The "Black," the "Olive" and the 

 lower portion of the "Ochreous" divisions of Rogers appear to 

 coincide with the Marcellus, Hamilton and Genesee (10a, b, c) 

 of the New York series ; while the higher portions of the ochre- 

 ous beds doubtless represent the equivalents of the Portage and 

 Chemung groups (11a, b). In many of the valleys where 10a, b 

 slates form very conspicuous features of the topography in the 

 form of slaty ridges and knobs of various size and shape, beds 

 of 11a, b, if they ever constituted a prominent feature, have been 

 almost entirely removed by denuding agencies. The remaining 

 slates of 10a, b, c have been so much crushed and warped by 

 the compressing forces exerted by elevation of the bordering 

 sandstone ridges, that it is difficult to determine their thickness 

 with certainty. But in the middle portion of the range, at 

 points where they have been least disturbed and least worn 

 clown by erosion, as for example, in parts of Bath and Alle- 

 ghany counties, we have found them to have an average thick- 

 ness of about 750 feet. In the higher parts we find some beds 

 of limestone containing remains of corals, crinoids and mollusks 

 of Devonian type. 



Catskill group, IX, R. (12). — This series of strata evidently 

 constitutes a transition period from Devonian to Carboniferous 

 age. Its lithological features as represented in its numerous and 

 heavy beds of brown micaceous sandstones, its conglomerates 

 and ochreous shales, and what remnants it contains of vegeta- 

 ble and animal life, although distinctly Devonian, all sug- 

 gest at least an approaching resemblance to what we find in the 

 overlying, and essentially conformable, beds of the Sub-carbon- 

 iferous period. 



Sub-carboniferous, X, XI, R. (13 a, b.) — The two divisions of 

 the Sub-carboniferous group are quite well characterized in Vir- 

 ginia, especially in the middle and southwestern parts of the 



