98 THE DEVONIAN AND CARBONIFEROUS. [bull. 80. 



In 1876 ! Mr. Stevenson classified the formations of Greene and Wash- 

 ington Counties. In his classification the Waynesburg sandstone is 

 made the base of the Upper Barren series. 



This is divided into two groups, called the Washington County group 

 and the Greene Couuty group. 



The first, or lower, includes the rocks from the Waynesburg sand- 

 stone to the Upper Washington limestone, inclusive. The second, or 

 Greene County group, extends from the top of the Upper Washington 

 limestone to the top of the series. 



The second distinguishing horizon is the Pittsburg Coal Bed, and the 

 series between it and the Waynesburg sandstone is the Upper Pro- 

 ductive Coal series. 



Below this the Lower Barren series is the name applied to all the 

 rocks down to the Mahoning sandstone. 



The rocks below the Mahoning sandstone are the Lower Productive 

 Coal series, the bottom of which is not seen in the counties under exam- 

 ination. 



Several local names are applied to the various strata presenting 

 conspicuous exposures in these counties. These are not of importance 

 for the purpose of this paper. 



In 1877 2 the same author reported upon the rocks of Fayette and 

 Westmoreland Counties. 



In this classification the Waynesburg sandstone, the Pittsburg 

 coal bed, the Mahoning sandstone, and the Pottsville (Serai) conglom- 

 erate form the conspicuous landmarks in the sections by means of which 

 the four divisions of the coal measures are separated. 



Below the Pottsville conglomerate the Umbral series of Eogers are 

 recognized, and the author reports the probable identification of fossils 

 from the limestones of this series in West Virginia with fossils of the 

 Chester limestones of the Mississippi Valley. 3 



The Sharon coal group is placed in this series below the Pottsville 

 conglomerate. 4 



The Pocono (Vespertine) rocks include the rocks of the district be- 

 low the Umbral limestone. 5 



In the following year (1878) Mr. Stevenson's third report 6 was pub- 

 lished. In this report are particularly discussed the rocks of the section 

 in the Ligonier Valley, Fayette and Westmoreland Counties. As in his 

 previous reports, Mr. Stevenson adopts in general the nomenclature 

 and classification proposed in the first geoogical survey. In this and 



1 Geol. Survey of Pennsylvania, Kept, of Progress K : Keport on Greene and Washington Counties, 

 by J. J. Stevenson, pp. 419, 1876. 



2 Geol. Survey of Pennsylvania, Kept, of Progress K 2 : Report of progress in the Fayette and West- 

 moreland district of the bituminous coal fields of Western Pennsylvania. By J. J. Stevenson, pp. 

 437. 1876. 



3 Ibid., pp. 102, 103. 

 4Ibid.,p.l03. 



6 Ibid., p. 105. 



6 Geol. Survey of Pennsylvania, Kept, of Progress K 3 : Report of progress in the Fayette and West- 

 moreland district of the bituminous coal fields of Western Pennsylvania. By J. J. Stevenson, pp. 

 331, 1877. 



