I9II.] STEVENSON— FORMATION OF COAL BEDS. 103 



These pebbles, he had discovered, are much more numerous than had 

 been supposed. They are covered with a carbonaceous patine and 

 are found mostly in the lower portion of the beds ; he never saw any 

 in the upper portions. The patine suggests that the pebbles may have 

 made a long journey in fermenting pulp, and he thinks that their 

 presence with this coating is confirmatory of Renault's opinions re- 

 specting the conditions of deposition of materials composing the coal. 

 At the same time, the " French theory " of the origin of coal, though 

 probable for the ensemble of the coal formation, does not explain the 

 underclay. As for Belgium, the special, the constant facies of the 

 mur is evidence of formation in place. The convincing fact is the 

 presence of Stigiiiaria in the mur with interlacing of the rootlets. 

 Stigiiiaria remains in the roof are fragmentary. 



In 1897, Schmitz reviewed Potonie's paper on Autochthonie ; he 

 recognizes that the mur is autochthonous but is not satisfied that that 

 necessarily involves the conclusion that the coal itself is autochthon- 

 ous also. A mur without coal is evidence of erosion, that its vege- 

 table cover has been washed away. If there be coal without mur, it 

 is allochthonous. A thick bed may be autochthonous below and 

 allochthonous above. While recognizing the valency of many of the 

 arguments presented by Potonie, he is not convinced that they are 

 final. 



In 1906, he reviewed the whole subject. His own position in 1896 

 was that of uncertainty between the old doctrine of autochthony and 

 the new forms of allochthony presented by Fayol and Grand' Eury. 

 Many phenomena observed in the Belgian basins seemed to support 

 Fayol's hypothesis, but the mur, with Stigiiiaria, clearly in loco iiatali, 

 is a fact which cannot be ignored. Autochthony found its chief sup- 

 port in conditions observed in recent swamps, but the knowledge 

 of those was too imperfect to make the argument wholly satisfactory ; 

 so that Schmitz. at that time, was inclined to hold an intermediate 

 position and to think that both doctrines might be true. 



But Potonie's later publication.^'^- based on the study of swamps 

 in a great area, goes far toward removing objections. Schmitz sum- 

 marizes the processes described as occurring in the formation of 



^''" " Die Enstehung der Steinkohle." 



103 



