I9I3.] STEVENSON— FORMATION OF COAL BEDS. 33 



pearance, though still distinctly peat ; but on the border of the valley, 

 where the marl is thick, the peat has been compressed to 3 inches and 

 has become a brown coal, hard, fragile and with brilliant fracture. 

 G. M. Dawson* found on Belly river, a bed of interglacial peat, 

 hardened by pressure so as to have the appearance of lignite. 



Brown coal or lignite exhibits a more advanced stage of chemical 

 change and is the ordinary type in Mesozoic and Tertiary deposits, 

 though it is not wanting in the Quaternary, for the beds at Diirnten 

 and elsewhere in Switzerland as well as at localities in Bavaria must 

 be accepted in great part as brown coal. At times, vegetable struc- 

 ture is thoroughly well preserved, especially where stems of trees are 

 present ; at other times, the whole mass is amorphous, while at still 

 others, both forms occur in a single layer, recalling the condition so 

 often seen in mature peat. Lamination is reported from many localities. 

 The color varies from dingy brown to coal black and the luster from 

 earthy to briliant, but the streak is 'brown. Brown coal is not un- 

 known in Palaeozoic deposits. The great beds of the Decazeville 

 basin, France, two of which have a maximum thickness of more than 

 100 feet, show all external characteristics of stone coal, but they 

 contain more oxygen and nitrogen than is found in ordinary brown 

 coal and more than twice as much as is present in air-dried stone 

 coal.^ The brown coal from Tula in Russia has been studied by 

 many palseobotanists. In spite of its ancient origin, it approaches 

 very closely to lignites in appearance and composition. Nikitin*' 

 states that there are several beds, more or less important, in the 

 lowest part of the Carboniferous and that boghead is associated with 

 the coal. In this connection, it may be well to recall the remarkable 

 observation by David, '^ which appears to have been overlooked. He 

 discovered in soft fine clay of Carboniferous age thickly matted 



* Cited by J. W. Dawson, " Canadian Ice Age," 1892, p. 724. 



' N. Saint-Julien, cited by J. J. Stevenson, " The Coal Basin of Decaze- 

 ville, France," Ann. N. Y. Acad. Sci., Vol. XX., 1910, p. 272. 



' S. Nikitin, " De Moskou a Koursk," Guide des excurs. VII., Cong. Geol. 

 Int., 1897, XIV., p. 5- 



^T. W. E. David, Ann. Rep. Dept. of Mines, New South Wales, 1890, 

 p. 229. 



PROC. AMER. PHIL. SOC. LII. 2o8 C, PRINTED MAY I3, 1913. 



