STEVENSON, COAL BASIN OF DECAZEVILLE, FRANCE 273 



high quickly develops an internal temperature of 60° C, and, if neg- 

 lected, ignites within a few days. The zinc company at Viviez, two 

 miles from Decazeville, stored a great quantity of the coal in a heap 

 somewhat more than 8 feet high. The rapidly increasing temperature 

 was discovered just in time to prevent destruction of the mass. The 

 danger is always present at outcrops, new or old. Fifteen jets of smoke 

 were seen at one time on the easterly wall of the Decazeville decouverte, 

 where the watch to prevent conflagration is incessant. Everywhere in 

 the great decouvertes the ravages of spontaneous combustion are proved 

 by areas of whitened surface and cindered rocks. Some of the under- 

 ground workings are charged with grisou and miners use only safety 

 lamps. The Campagnac coal has the same tendency, but it is less marked, 

 for an official of the company at Cransac stated that heaps eight feet 

 high are safe. The sulphur in these coals is not excessive, little more 

 than one per cent. 



In this connection, it may be well to note that the Campagnac bed is 

 separated at most by two or three yards from the overlying conglomerate 

 beds, open-grained rocks, while the Bourran bed underlies a great thick- 

 ness of more or less argillaceous deposits, close-grained rocks. If the 

 process of transformation continue to any great extent after burial of the 

 coal material under the inorganic load, the Campagnac coal should show 

 a greater difference from that of the Bourran than is indicated by the 

 analyses ; the more so as they are separated by an interval of 750 feet. 



The writer's purpose in studying the Decazeville basin was to ascertain 

 whether or not the conditions existing there favored the doctrine that 

 coal beds are composed of transported vegetable matter. Any hypothesis 

 offered to account for formation of the coal beds must take into consider- 

 ation certain important features of the basin, such as 



The original extent and character of the basin, 



The manner in which the mineral detritus was deposited and the 

 features of the streams which did the work. 



The extent and distribution of the coal beds. 



Certain structural features, such as the folding and faulting, being of 

 later origin, have no bearing upon the general question. 



THE ORIGINAL EXTENT AND CHARACTER OF THE BASIN 



The Decazeville Coal Measures occupy a depression in the Archean 

 schists and are bounded, at least in part, by faults which have no direct 

 relation to those observed within the basin. 



