194 C. S. Prosser — Names for the formations 



River system to cover all the rocks from the highest Upper 

 Barren Measures to the base of the Upper Productive Coal 

 Measures, while those included between the horizon last men- 

 tioned and the top of the Pottsville conglomerate were called 

 the Allegheny River system. 



Lesley also in the same year divided the Carboniferous system 

 into first the Monongahela River Coal Series, which included 

 the rocks from the highest of the Upper Barren Measures to 

 the base of the Upper Productive Coal-measures, and second 

 the Allegheny River Coal Series, which apparently comprised 

 all the rocks from the top of the Lower Barren Measures to 

 the base of the Pocono sandstone.* 



In some respects these modified classifications appear less 

 desirable than the original one and, according to the practice of 

 the U. S. Geological Survey which is now quite generally fol- 

 lowed by American geologists, the names Monongahela and 

 Allegheny having already been used for divisions of smaller 

 rank, were not available as names for these two divisions. 



In 1876 Prof. Stevenson divided the Upper Barren series 

 into two groups, the upper one termed the Greene County 

 group, which included all the rocks above the Upper Washing- 

 ton limestone ; and the lower one, named the Washington 

 County group, which extended from the top of the Washington 

 limestone to the top of the Waynesburg sandstone, .an horizon 

 some 80 feet above the Waynesburg main coal.f 



Professors Fontaine and I. C. White carefully studied the 

 flora of the Upper Barren Measures and reached the conclusion 

 that the " Upper Barrens of the Appalachian coal field are of 

 Permian age."J 



In 1891 Dr. I. C. White published his excellent work on the 

 ci Stratigraphy of the bituminous coal fields of Pennsylvania, 

 Ohio and West Virginia, " in which he named the Upper Bar- 

 ren Measures the Dunkard Creek series,§ stating that " the 



rocks of this series begin with the roof shales of the 



Waynesburg coal and extend upward to the topmost beds of 

 the Appalachian region." | 



In 1896 Messrs. K H. Darton and Joseph A. Taff published 

 a description of the geological formations of the Piedmont 

 folio, covering the southern part of the extreme western portion 

 of Maryland and a larger area to the south of the North Branch 

 of the Potomac river in the northern part of West Virginia. 

 TJiey gave new names to the Coal-measure formations derived 

 from geographic names occurring in the Piedmont quadrangle, 

 and in general the formations were not separated as they were 



*Seeond Geol. Surv. Penna., H 3 , 187T, p. xxiii. f Ibid., K, p. 35. 



% Ibid., Report PP, 1880, p. 119. 



§Bull. U. S. Geol. Surv., No. 65, p. 19. || Ibid., p. 20. 



