Campbell — Rogers's Geology of the Virginias. 371 



lithological and paleontological features. The shales become 

 more ferruginous as well as more siliceous. In fact some of the 

 highest beds become really argillaceous sandstone of a purplish 

 color with thin layers of similarly colored' shales intervening. 

 This part of the formation is in many portions of its range the 

 repository of valuable ores of iron. 



Prof. Rogers gives a very good view of some of the leading- 

 exposures of his No. Ill (4&, c.) " This member of the series 

 consists of slates and slaty sandstones, of various shades of 

 bluish black, lead color and yellowish brown, the dark varieties 

 in general predominating. Their structure is laminated and 

 fissile, not unfrequently evincing the presence of small quanti- 

 ties of mica. When weathered they in most cases assume a 

 yellowish or dingy brown appearance. Usually this slate is 

 devoid of carbonate of lime, though bands are occasionally met 

 with containing organic impressions, and of a composition more 

 or less calcareous. Iron pyrites is of very common occur- 

 rence, giving origin to the sulphurous impregnation of numer- 

 ous medicinal springs taking their rise in these rocks. . . . 



" Resting immediately upon the upper boundary of valley 

 limestone, No. II (3c) this rock or group of strata is exhibited 

 on a very extensive scale along the base and flanks of the 

 Peaked Mountains and the Massanutten, and other parallel 

 ranges in Shenandoah, Rockingham, Page and other counties. 

 From the synclinal structure of most of these ridges, the slate 

 is exposed on both sides of the mountain, dipping inward, 

 that is, to the N.W. on the eastern side and S.E. on the western 

 side. The striking symmetry of contour exhibited by the 

 Peaked Mountains [southwest terminus of the Massanuttens], 

 when viewed endwise from a point south of the termination 

 of the range, illustrates the basin-shaped arrangement of the 

 strata of slate resting in a trough of subjacent limestone, and 

 surmounted by the sandstone which forms No. IY (5a) of our 

 series. There are few, perhaps no other, exposures in the slate 

 in which the structure and relations of these beds can be so 

 satisfactorily observed, as in the group of mountains here re- 

 ferred to. .". . " (p. 174). 



" It has been seen that this formation, constituting abroad 

 belt extending from the Potomac far into the middle counties 

 of the valley, constitutes a great synclinal trough, the northern 

 portion of which stretches far into Maryland, sustaining for a 

 considerable part of its length in Virginia, the group of long 

 parallel ranges called the Massanutten Mountains. . . . Under 

 like circumstances this formation is found constituting the 

 trough-shaped basis on which the higher formations repose in 

 the House Mountains, Short's Hill and Purgatory Mountains. 

 In the House Mountains, the slate forming the base and extend- 



