192 C. S. Prosser — Names for the formations 



of which was not so sharply defined, although it was stated in 

 general that it rested directly on the conglomerate ; but in the 

 anthracite region, where the two are closely united, Prof. 

 Rogers reported that " considerations of convenience dictate 

 that we place an arbitrary boundary at the bottom of the first 

 or lowest considerable coal-seam."* The Upper or Newer Coal- 

 measures were defined as extending " from the bottom of the 

 Pittsburg coal to the top of the Waynesburg seam,"f and the 

 Upper Barren group contained the remainder of the coal rocks 

 which were found in the southwestern corner of the state. 



From this classification has come the one in general use, 

 which is stated as follows, by Dana, in the last edition of his 

 Manual : 



Upper Barren Measures. 



Upper Productive Measures. 



Lower Barren Measures. 



Lower Productive Measures.^ 



In 1872 Prof. Stevenson described the Coal-measure for- 

 mations as shown in Monongalia and Marion counties, West 

 Virginia, stating that he " thought it best to adopt the terms 

 used in the Geology of Pennsylvania and the Virginia Reports, 

 for, though they may not have been based on scientific grounds, 

 they are most convenient for description, as the rocks are here 

 developed. "§ Under the descriptions of the formations, or 

 groups as they were termed, names derived from geographical 

 terms were used as synonyms for the Lower and Upper Coal 

 groups, the limits of which differed somewhat from those 

 fixed by Rogers. 



The Lower Coal group or Allegheny river series extended 

 from " the Great Conglomerate " to the top of the Mahoning 

 sandstone.] The base of the formation was drawn at a lower 

 horizon than has generally been the case in later classifications, 

 for it included the Tionesta sandstone and coal (Coals Nos. 18 

 and 20 of the section), while the higher coal (No. 14 of the 

 section) was correlated with the Brookville, which later has 

 come to be regarded as very near the base of the Allegheny 

 formation. The upper limit of the formation at the top of the 

 Mahoning sandstone also differed from that of the Lower Coal- 

 measures of Rogers, which was drawn at the top of the Upper 

 Freeport coal at the base of the Mahoning sandstone. 



The Upper Coal group or Monongahela river series extended 

 from the base of the fire clay immediately underlying the Pitts- 

 burg coal to the top of the Waynesburg sandstone, which was 

 given as from 31 to 55 feet above the top of the Waynesburg 

 coal,T while the Upper Coal-measures of Rogers extended 



* Geology Pennsylvania, vol. i, 1858, p. 11. f Ibid., p. 19. 

 % itfanual of Geology, 4th ed., 1895, p. 648. 

 § Trans. Am. Phil. Soc. Philadelphia, 2d Ser., vol. xv, p. 16. 

 1 Ibid., pp. 27-30. f Ibid, p. 11. 



