I9I3.] STEVENSON— FORMATION OF COAL BEDS. 43 



Hantken^^ gives a section at a Hungarian locality showing 8 coal 

 beds from 0.15 to 3.10 meters thick, of which four have clay and 

 four have sandstone as the floor. Coal deposits were formed on 

 clay, shale, sandstone or even limestone, the conditions being ap- 

 parently the same as those observed in the study of peat accumu- 

 lations. The Triassic coal of the Richmond area in Virginia was 

 long supposed to rest on granite. Taylor^" mentioned the recognized 

 fact that the coals of that area rest directly on granite, though 

 occasionally a foot or two of shale may intervene. Bosses of 

 granite rise as eminences and interfere with mining. This opinion 

 was shared by W. B. Rogers in 1843 ^^^ ^^ ^ later date by Lyell, 

 who asserted that the lower coal bed is in contact with the funda- 

 mental granite. The true condition was ascertained by Shaler and 

 Woodworth,-° who showed that the granite contact is due to faulting 

 and that, normally, there is a notable interval, sometimes 300 feet, 

 filled with barren rocks. There is no a priori reason, however, why 

 coal might not accumulate on a granite seat. Chevalier's descrip- 

 tion of the peat growth on granite and gneiss in the Niger region 

 makes this clear enough. 



Cores from diamond drilled holes in the anthracite areas of 

 Pennsylvania indicate in many cases that coal beds of notable im- 

 portance rest directly on conglomerates or are separated from them 

 by a mere film of clay. The cores show all gradations in the floor 

 from fine clay to conglomerate. Similar conditions exist elsewhere. 

 The hard silicious rock, known as " Ganister,"^^ is at times in con- 

 tact with the overlying coal bed in the Yorkshire field. Sections in 

 other British fields show that a sandy floor is a by no means un- 

 common feature, though clay is the usual material. 



Limestone of marine or freshwater origin is frequently the floor 



" M. Hantken, "Die Kohlenflotze und der Kohlenbergbau in den Landern 

 der ungarischen Krone," Budapest, 1878, p. 131. 



^' R. C. Taylor, " Memoir of a Section Passing through the Bituminous 

 Coal Field near Richmond in Virginia," Trans. Geol. Soc. Penn., Vol. I., 

 Part IL, 1836, pp. 286, 287. 



^'' Nf S. Shaler and J. B. Woodworth, " Geology of the Richmond Basin, 

 Virginia," 19th Ann. Rep. U. S. Geol. Surv., 1899, Pt. II. , pp. 424-426,429,430. 



"A. H. Green, "The Geology of the Yorkshire Coal Field," 1878, pp. 19, 26. 



