191^.] STEVENSON— THE FORMATION OF COAL BEDS. 445 



eiice of angular and rounded fragments of Coal Measures rocks 

 with pebbles of coal in the lower part of the Permian. 



Andrews^^ found in the lower part of a sandstone overlying the 

 Nelsonville coal bed a rounded fragment of coal, measuring 4 by 

 2 inches. It bears so close resemblance to coal from Straitsville, 

 only a few miles away, that he believed it derived from that place — 

 the coal bed being the same at both localities. This great coal 

 deposit is only 200 feet above the bottom of the Ohio Coal Measures. 

 Andrews is convinced that the coal had been completely formed by 

 the time that 12 feet of shale and one foot of sandstone had ac- 

 cumulated at Straitsville. He observed irregular fragments of 

 coal, some angular, others rounded, in a sandstone w^ithin Wayne 

 county of West Virginia. 



Jordan^^ states that the Welsh Coal Measures are divisable into 

 the Pennant Grit above, with few coal seams, and a lower division, 

 mostly shale, with numerous coal seams. He found no coal pebbles 

 in the lower division, but in the lower part of the Pennant they are 

 present, associated with pebbles of granite. Logan's pebble of 

 cannel was found in slate overlying a bed of ordinary coal and was 

 supposed by him to have been derived from a bed, 2,000 feet lower 

 in the series. Jordan objects that there is no evidence that the 

 lower beds were upraised and denuded before deposition of the 

 upper beds. He thinks that the pebbles were derived " either from 

 the seam of coal above which they are found or from the destruction 

 by erosion of a seam of coal, which once existed approximately in 

 the position in which they are found, the erosion in either case being 

 effected by the strong water courses which distributed the grains of 

 sand and other material upon the coal seam." He refers to the 

 "Rock Fawr" seam near Bridgend, where the sandstone roof con- 

 tains a notable quantity of slightly rounded pebbles of coal, similar 

 to those of the underlying seam. Logan's pebble, he thinks, came 

 from a superficial layer of cannel in the Penslawdd seam. The 



^' E. B. Andrews, Ohio Geological Survey, Vol. I., Part I., 1873, pp. 



355-357- 



^" H. K. Jordan, " On Coal Pebbles and their Derivation," Quart. Journ. 

 Geol. Soc, Vol. XXXIII., 1877, pp. 932, 933- 



