44 STEVENSON— FORMATION OF COAL BEDS. [April iS, 



of a coal bed. Several coal beds in tbe Monongahela and higher 

 formations within the Appalachian basin rest at times on fresh- 

 water limestone or calcareous shale; at others clay or shale inter- 

 venes, so that in different parts of the area the same coal rests on 

 clay, shale, sandstone or limestone. Two coals of the Conemaugh in 

 Ohio show similar relations to a marine limestone, sometimes in 

 contact with it, at others, separated by several feet of shale or other 

 material."- C. Robb in 1876 reported 6 inches of limestone directly 

 vnider a Canadian coal bed, and J. W. Dawson in 1868 described a 

 coal bed which overlies a bituminous limestone, containing Naia- 

 ditcs and Stigniaria, the latter, in his opinion, being evidently in 

 place. Not many instances of coal resting directly on marine lime- 

 stone are recorded from the Appalachian basin, because, with one 

 exception, the marine limestones are, geographically considered, very 

 unimportant members of the column. Nor is the occurrence fre- 

 quent in any field, so far as the writer can discover, though there 

 are many localities where the interval is not more than a foot. 

 Worthen states that the Coal i of Illinois usually overlies 2 to 3 

 feet of fireclay, but the fireclay is often absent and the coal rests 

 directly on the St. Louis limestone. This, however, is not of the 

 type under consideration, for the case is one of pre-Pennsylvanian 

 erosion ; the Illinois Coal 5 occasionally rests on a nodular lime- 

 stone and Coal 6 is frequently in contact with the underlying marine 

 limestone. Ricketts has described a number of coal pockets in 

 Lower Carboniferous limestone of England but they do not concern 

 the matter in hand, for they are clearly like the Iowa and Missouri 

 pockets, in cavities eroded when the limestone was above water. 



Crampton,-^ however, has given notes which do concern the 

 matter. Presenting the results of studies in East Lothian, Scotland, 

 he refers to the lowest limestone as essentially a coral reef with an 

 abundant marine fauna. Portions of the surface were converted 



^' J. J. Stevenson, Sec. Geol Surv. Penn., Rep. K, 1876, pp. 94, 96, 116, 270, 

 349; Rep. KK, 1877, PP- 52, 163, 179; "Geology of Ohio," Vol. III., 1879, pp. 

 183, 211, 224, 240, 256. 



-^ C. B. Crampton, "The Limestones of Aberlady, Dunbar and St. Monans," 

 Trans. Edinb. Geol. Soc, Vol. III., 1905, pp. 374-378; "Fossils and Condi- 

 tions of Deposits, a Theory of Coal Formation," ibid.. Vol. IX., p. 74. 



