1913.] STEVENSON— FORMATION OF COAL BEDS. Ill 



commonly regarded as requiring deep water. The Middle Kittan- 

 ning in much of Ohio is easily recognized by means of its marine 

 shale roof. Lesquereux has mentioned several instances in Ken- 

 tucky and the Pennsylvania geologists have added many more. 

 Absence of plant remains is reason for suspecting that the shale is 

 not a terrestrial deposit, even though remains of animals appear 

 to be wanting. Boulay^^^ was puzzled in several instances by a roof 

 apparently normal but without trace of plants. Very close examina- 

 tion revealed an exceedingly thin layer with Mytilus at 4 or 5 inches 

 above the coal. In many cases within American coal areas, the pre- 

 vailing forms in the roof are Lingula and Orhiculoidca, which are 

 shallow water forms, but there are roof shales, usually somewhat 

 sandy, containing Productus, Spirifer and other forms which belong 

 to the so-called deep-water fauna. The condition is quite common- 

 place in modern times. Instances of peat deposits directly under- 

 lying marine clays and sands were given on preceding pages and 

 many additional instances could be cited if necessary. 



Limestone is by no means an uncommon roof; it is characteristic 

 of several coal beds within the Beaver formation. I. C. White has 

 recorded many instances in Pennsylvania ; Orton, Jr. and A. A. 

 Wright have done the same for Ohio and I. C. White reports the 

 same condition at localities in southern West Virginia. At all of 

 these localities the limestone is marine ; but contact with the coal is 

 not found throughout, for very frequently the coal and limestone, 

 in contact at one locality, are separated by several feet of shale or 

 even sandstone at others. The lowest coal bed of the Allegheny in 

 Ohio often is in contact with the overlying marine limestone, and 

 the Harlem coal bed of the Conemaugh is at times directly under the 

 marine Ames limestone, though usually a considerable mass of shale 

 intervenes. So in the Illinois field where Worthen^^" found his 

 coals III. and VI. with a marine limestone roof. This is not un- 

 usual enough to be surprising; some instances have been reported 



"' I'Abbe Boulay, " Recherches de paleontologie vegetale dans le terrain 

 houiller du Nord de la France," Ann. Soc. Scient. de Bruxelles, 4me annee, 

 1879, Sep., pp. Zi, 47, 57-59- 



"•A. H. Worthen, Geol. Surv. Illinois, Vol. III., 1868, pp. 12-13. 



