J. J. Stevenson — Lower Carboniferous groups. 37 



Art. V. — Notes on the Lower Carboniferous groups along the 

 easterly side of the Appalachian area in Pennsylvania and the 

 Virginias ; by John J. Stevenson, Prof, of Geology in the 

 University of the City of New York. 



The division of the Lower Carboniferous into Urabral and 

 Vespertine, as made many years ago by the Professors Rogers, 

 holds good along the easterly side of the Appalachian area cer- 

 tainly into Tennessee. But these 'groups show notable varia- 

 tions in thickness and in character of the rocks, not only along 

 lines from southeast, to northwest but also along the line of 

 strike, or from northeast or north-northeast southwardly. The 

 writer has had opportunity to study these variations somewhat 

 in detail within the southern counties of Pennsylvania as well 

 as in the southwestern part of Yirginia beyond New River to 

 the Tennessee line, and to some extent at widely separated 

 localities in West "Virginia. 



The Umbral within Pennsylvania is, for the most part, a 

 mass of red shales and shaly sandstones and is so well shown 

 as such in the Anthracite region that Prof. Lesley has renamed 

 it the Mauch Chunk. Some thin beds of limestone, first seen 

 near the Maryland line along easterly outcrops, increase west- 

 wardly and become important at the last exposures under 

 Chestnut ridge in Fayette County. But the thickness of the 

 group diminishes as the limestone increases, being little more 

 than 200 feet in Fayette,* whereas it is about 1100 feet in 

 Fulton County. 



The Yespertine in central and south-central Pennsylvania 

 shows sandstone and shales with occasional streaks of coal. 

 The sandstones vary from fine-grained to moderately conglom- 

 erate and the shales are irregular in thickness and character. 

 The variations in thickness are not unlike those of the Umbral, 

 the decrease being from somewhat more than 1300 feet in 

 Huntington County (as determined by Prof. I. C. White) to not 

 far from 400 feet in Fayette County. The topmost member of 

 the group is a calcareous sandstone, the siliceous limestone, 

 which first appears in Huntingdon County (White) and thick- 

 ens toward the west. This is the " Ligonier paving stone," 

 much used in Pittsburgh and other cities. In the writer's 

 Pennsylvania reports, this is placed as a member of the Um- 

 bral, but its relations are rather with the Yespertine. 



s The thickness given for Fayette county is barely half that assigned to the 

 group in the writer's report on the geology of that county. The writer is con- 

 vinced that the upper portion belongs not to the Umbral but to the Lower or 

 Conglomerate Coal Measures. 



