I9I3.] STEVENSON— FORMATION OF COAL BEDS. 75 



sistent members of the column. The Canister, when separated by 

 several yards from the upper Foot, contains no balls ; but when the 

 parting is only a few inches, the balls are in both beds. There is no 

 regularity in the distribution. The Hard coal bed, near Halifax in 

 Yorkshire and belonging apparently at the same horizon, also con- 

 tains similar balls. These concretions have a slickensided surface 

 and the coal laminse curve around them ; occasionally a faulted 

 specimen is found. In size they vary from an inch to a foot or even 

 more — one, near Shore, weighs 2 tons and replaces the coal from 

 roof to floor. These balls in the coal contain plant remains in condi- 

 tion of remarkable preservation. 



The roof shale of this coal bed carries abundant remains of 

 marine animals along with much fragmentary plant material. 

 " Bullions," " baumpots " or " Goniatite nodules " occur in this shale 

 and are as characteristic of it as the coal balls are of the coal. These 

 roof balls enclose shells with which there are often bits of plants, 

 rarely well preserved but at times admitting of generic determina- 

 tion. Sphserosiderites, answering to the English roof balls or bul- 

 lions, have been found within the Nord (France) basin in marine 

 shales, sometimes resting on thin coals. They, like the English balls, 

 contain Goniatites, Productus and other forms ; but Barrois does 

 not note the presence of similar concretions in the coal. 



Sphaerosiderites were obtained at collieries in the Ostrau coal 

 field from the roof shale of the Heinrichs and Coaks coal beds ; in 

 each case the shale is marine. The balls from the higher shale are 

 occasionally fossiliferous but those from the roof of the lower bed 

 seem to be without fossils. The lower part of this shale, however, 

 is crowded with small balls of pyrite, many of which are fossil- 

 iferous, while many shells in this portion have been replaced with 

 pyrite. The balls, for the most part, are small, very irregular in 

 form and often are polished, so that they might easily be mistaken 

 for erratics. Sometimes several are united but ordinarily they are 

 separate and are scattered throughout the shale. They are encrusted 

 with powdery matter, one to two millimeters thick, which is re- 

 moved readily by washing. When exposed to the weather, their 

 concretionary structure soon becomes apparent. 



