I9I3-] STEVENSON— FORMATION OF COAL BEDS. 67 



was shallow and far from clean, but the characteristic fossils per- 

 sist to the last exposure of the horizon. Bownocker has noted a 

 number of localities in Meigs, Gallia and Lawrence counties of Ohio, 

 all on the western border, where this limestone is impure, argillace- 

 ous, ferruginous or sandy, yet the fossils persist. I. C. White found 

 the same conditions along the northern border in Pennsylvania. 

 Hennen*^° reports that in Harrison county of West Virginia, where 

 one approaches the southern limit of the Ames limestone, the rock 

 is an impure limestone, often represented only by dark limy shale 

 but always containing the same marine fossils. The Conemaugh 

 formation has other marine limestones which are brecciated at 

 numerous localities. In some cases the shells are broken as on a 

 shore. 



The Occurrence of Cannel. 



The cannels and bogheads differ from true coals not merely in 

 structure and composition but also in their mode of occurrence.. 

 Cannel is invariably a local deposit, in the extreme sense of the 

 term, though conditions favoring its formation existed more fre- 

 quently at some horizons than at others. Many of the small isolated 

 basins in Iowa, Missouri and even in Pennsylvania contain only 

 impure cannel, but ordinarily the mineral forms part of a coal bed, 

 the relation being intimate. Invariably, the deposit is saucer-shaped, 

 as though occupying a depression in vegetable matter previously 

 accumulated. White*^^ has described a cannel of much commercial 

 importance, though it is confined to only one estate ; the mass has a 

 maximum thickness of 12 feet and thins away to nothing in all 

 directions. The changes are exhibited in extensive workings. Platt*'^ 

 examined, in Armstrong county of Pennsylvania, three disconnected 

 patches of cannel at the Upper Kittanning horizon. The space be- 

 tween these is occupied by ordinary coal. In each, the cannel is 

 from o to 8 feet thick; the bottom bench of the coal bed is bitumi- 

 nous and it is depressed with the thickening cannel, the slope of the 



*" R. V. Hennen, W. Va. Geol. Surv., County reports, 1912, p. 251. 



" I. C. White, Sec. Geol. Surv. Penn., Rep. Q, pp. 213, 232, 258, 259, 268. 



''W. G. Piatt, ibid., Rep. H5, p. 176. 



