UMBKAL SHALE GROUP. PP. 9 



This group, so far as known, contains in W. Ya. no 

 fossil plants. The subsidence causing the deposition of 

 this limestone, and the accompanying destruction of plant 

 life no doubt had an important influence in bringing about 

 the change which we find to have taken place in the flora 

 of the Conglomerate Series, which is the next plant-bear- 

 ing horizon above the Vespertine. 



The Umbral Shale Group. 



This group, in West Virginia, consists of shales and 

 sandstones of various hues and textures, and, where fully 

 developed, like the Vespertine group, possesses a trip- 

 pie character. The lower member consists of red, poorly 

 laminated shales or marlites, and red or brown, argil- 

 laceous sandstones. The shales are remarkable for their 

 deep blood-red color and crumbling, friable texture. The 

 middle portion is mainly composed of pretty siliceous sand- 

 stones, of a grey or white color ; grey flags ; and grey or 

 greenish marlites. The upper member is, like the lower, 

 composed of deep red shales and sandstones. On New 

 River, in the vicinity of Richmond Falls, the group appears 

 in great force. Here it is nearly 1500 feet thick. It shows 

 at this locality the triple division in a marked manner. 

 This group also is a shore formation, and reaches its great- 

 est development in the east, thinning out entirely as we pass 

 to the west. Like the Vespertine, it shows great variations 

 in thickness, even along the eastern border, and follows 

 nearly the same law of change. 



The following measurements will indicate the variations 

 in different quarters : 



Prof. Wm. B. Rogers finds it in Pocohontas Co. near 

 the White Sulphur to be about 1310 feet thick, while on 

 the Potomac River near Westernport, Md. he finds it to 

 be 738 feet thick. 



In Huntingdon Co. Pa. Mr. Ashburner finds 1100 feet of 

 Umbral Rocks, including 49 feet of Umbral or Lower Car- 

 boniferous Limestone, in several layers, f On Cheat River 

 in Monongalia Co. the interval between the Lower Carbon- 



[t And including also, in his 1100 feet, 141 feet of reddish and green Umbral 

 shales below the Limestone. — J. P. L.] 



