I 



liams.] CHANCE, STEVENSON. 119 



proposed nomenclature of the Carboniferous and Devonian rocks of 

 eastern Pennsylvania and Ohio." 



Eastern Pennsylvania. Western Pennsylvania. Ohio. 



Carb 5 X ? IJ ^ oal Measures Coal Measures Coal Measures. 



" I XII Conglomerate Conglomerate series Sandstone and shale 



with coals 1,2, ',\. 

 XI Mauch Chunk red 



shale Red or dark shales. 



Subcarb. { f Upper (gray) Pocono Cuyahoga and Berea 



X Pocono sandstone < T , , XT » ., , -r,^,}. , , , 



L I Lower (red) Pocono=oil- ( Bedford shale. 



t sand group. \ Cleveland shale. 



{IX Catskill Absent Absent, 

 f Chemung Chemung ) , ^ . , , 

 Portage" Portage.^ i J Erie shales. 

 VIII < Hamilton Hamilton (?) ) ' Huron shales. 



I Corniferous lime- Corniferous Corniferous lime- 



(, stone. stone. 



In order to explain the difficulties in correlating ttie deposits below 

 the great Conglomerate, No. XII, Mr. Chance assumed that there was 

 a basin during the deposition of the Catskill rocks, the western limits 

 of which swept approximately through Potter, Cameron, Elk, Jeffer- 

 son, Armstrong, and Westmoreland Counties ; that along this line, or 

 somewhat westward of it, a sudden rising into shallow water, or to 

 shore line conditions, prevailed in the Catskill and Pocono time. This 

 explains, as he thinks, the accumulation of oil-sands along such a shal- 

 low bottom, while further out the Catskill deposits were forming. 1 



Mr. Stevenson, 2 in 1887, presented some new views regarding the cor- 

 relation of the Umbral and Vespertine in the southern extension of the 

 Appalachian province. He stated that Prof. Roger's division of the 

 Lower Carboniferous into Umbral and Vespertine, seems correct for 

 the eastern side of the Appalachian area, but in southern Pennsylvania 

 and Virginia there are variations worthy of study. 



The Umbral deposits in Pennsylvania consist of red shales and shaly 

 sandstones, and were afterward called by Prof. Lesley the "Mauch 

 Chunk." 



The limestones first noticed in Maryland increase rapidly in thick- 

 ness westwardly. 



The Vespertine consists of sandstone and shales, with occasional coal 

 seams, and varies in thickness from 1,300 feet in Huntingdon County 

 to 400 feet in Fayette County. 



Owing to the faulted condition of the rocks in southwest Virginia, 

 good sections of Lower Carboniferous rocks are shown from the Ten- 

 nessee line to Giles County. The rocks do not change materially until 

 we come within 75 miles of the Tennessee line. In this direction the 

 Vespertine thins out more rapidly than the Umbral rocks, which in 

 Pulaski and Bland Counties contain streaks of coal. In Smyth County, 



•A diagram is given illustrating this view on i>. 1 14 of the Report. 



* Stevenson, J.J. : Notes on the Lower Carboniferous groups along the easterly side of the Appa- 

 Uchian area in Pennsylvania and the Virginias. Am. Jour. Sci., 3d ser., vol. 34, 1887, pp. 37-44. 



