452 STEVENSON— THE FORMATION OF COAL BEDS. [Nov. i, 



the surface is smooth, metallic and lustrous, often with a scale-like 

 coating such as one sees on concretions. They are separated easily 

 from the surrounding coal, to which they are not related, and they 

 do not occur in the associated rocks. Gothan considers the various- 

 suggestions offered to explain the occurrence of these nodules, but 

 finds them either insufficient or not in accord with the conditions. 

 He seems to be convinced that they are pebbles, owing their rounded 

 form to attrition. The Geological Survey collection at Berlin con- 

 tains similar forms from a mine in the upper Silesian Carboniferous^ 

 where the pebbles of coal are associated with others of quartzite,. 

 granulite, etc. There and at other localities the association is evi- 

 dence of transport, but, at Vasas, rock pebbles are unknown. 

 Gothan sees no reason to suppose that they came from a distance. 

 He conceives that they may have been formed even while the 

 Jurassic Waldmoor existed and that wind-moved water may have 

 detached pieces of the harder peat. The more resistant portions of 

 those pieces would be rubbed against each other until rounded and 

 eventually they would sink into the peaty mud. These " balls "" 

 occur elsewhere. Hughes found*^ balls of very pure coal enclosed 

 in coal beds in India and Stainier reports that at Turon in Asturia 

 there is a bed formed wholly of rolled pebbles of coal ; he mentions 

 two localities in Australia, where coal pebbles are embedded in 

 coal of notably different composition and states that such pebbles 

 occur in the coal basins of Mons and Charleroi, Belgium. 



These citations sufifice to illustrate the varying conditions in 

 which coal pebbles or fragments occur in clastic rocks or even in 

 coal beds themselves. Gothan's explanation for existence of balls 

 in coal may account for origin of the material. A broad stream 

 meandering through a deep bog might easily tear oft' small frag- 

 ments, as supposed by him, but even then the necessity for trans- 

 port remains, since there could be no sufficient chafing in quiet or 

 gently moving water. In all other cases, the transportation is clear. . 



" T. Hughes. " The Jherria Coalfield," Mem. Geo!. Surv. India, Vol. V., 

 pp. 254-256; X. Stainier, " Des rapports entre la composition des charbons 

 et leur's conditions de gisement," Ann. des Mines de Belgique, Vol. V., 1900, 

 PP- 95-97- 



