74 STEVENSON— FORMATION OF COAL BEDS. [April i8, 



are rudely spherical but for the most part the shale is irregularly oval 

 and occasionally even plate-like. When enclosed in coal beds, the 

 laminae are displaced about them as though the final compression 

 had taken place after formation of the nodule ; and this feature is as 

 characteristic of coals which have not been distorted as of those 

 which have been folded. The nodules are often fossiliferous, con- 

 taining marine shells at times but land forms and plants at others — 

 as those obtained at Mazon creek in Illinois, in which are remains 

 of many animals as well as plants, all marvelously well preserved. 

 Such nodules have been found in the Devonian, for Nathorsf^- ob- 

 tained some from shales of that age in Spitzbergen ; Lepidodendron 

 and apparently Bothrodendron were recognized in several of them, 

 while others contain remains of fishes. 



More than 80 years ago, calcareous nodules more or less ferrugi- 

 nous, occurring in the roof and coal of a thin bed in the Lancashire 

 coal field, attracted Binney's attention and were made the subject 

 of a memoir by Hooker and Binney. Since that time, such nodules 

 have been discovered in many lands and have been investigated by 

 students in Europe. In this summary, reference is made only to 

 some of the later publications." 



Coal balls were supposed for a long time to be confined, in Eng- 

 land, to a single horizon, the thin Lancashire coal bed known as the 

 Mountain Upper Foot. This, in the Lower Coal Measures, is at a 

 variable distance above the Canister coal bed, one of the most per- 



"A. G. Nathorst, "Zur palaeozoischen Flora der arktisches Zone," Hand. 

 K. Svens. Veten-Akad., Band 26, No. 4, 1904, pp. 11, i3- 



" D. Stur, " Ueber die in Flotzen reiner Steinkohle enthaltenen Stcin- 

 Rundmassen und Torf-Sphaerosiderite," Jahrh. d. k. k. Geol. Reichsanst., 

 Vol. XXXV., 1885, pp. 628 et seq. ; A. Strahan, " On the Passage of a Seam 

 of Coal Into a Seam of Dolomite," Quart. Jouni. Geol. Soc, Vol. LVIL, 1901, 

 pp. 297-304; H. B. Stocks, "On the Origin of Certain Concretions in the 

 Lower Coal Measures," ibid., Vol. LVIIL, 1902, pp. 46-58; M. C. Stopes and 

 D. M. S. Watson, " On the Present Distribution and Origin of the Calcareous 

 Concretions in Coal Seams, known as ' Coal Balls,' " Phil. Trans. Roy. Soc, 

 Ser. B, Vol. 200, 1908, pp. 167-208; W. Gothan und O. Horich, " Uebcr 

 Analoga der Torfdolomite (Coal Balls) des Carbons in der rheinische Braun- 

 kohle," Jahrh. k. preuss. Landesanst., Band XXXI., Teil II., 1910, pp. 38-44; 

 C. Barrois, "fitude des strates marines du terrain houiller du Nord," i^e Partie, 

 1912, pp. 4, 9 38, 62. 



