STEVEN80N, COAL BASIN OF DECAZEVILLE, FRANCE 249 



the material. The deposit of conglomerate began very soon after accu- 

 mulation of the Campagnac coal bed. 



The Bourran system, beginning with the Grande Couche de Bourran, 

 known as N"egrins, Crol, Fraysse, Firmy, Bourran, Saint-Eoch at the 

 several mines, consists of shales and shaly sandstones succeeded by a con- 

 siderable thickness of coarse, more or less conglomeratic sandstone. It oc- 

 cupies the central and western parts of the basin ; and a small area, caught 

 in the jaws of faults, remains on the eastern side near Firmy. The 

 studies by Bergeron, Jardel and Picandet leave little room for doubting 

 that practically all of the water-carried deposits west from the central 

 line of the basin date from the beginning of the Bourran system. 



The Decazeville basin, unlike that of Commentry, is characterized by 

 great irregularity of structure, the beds being folded and faulted in com- 

 plicated fashion. The folds will be noted in the local descriptions, but 

 the principal faults must l)e mentioned here that those descriptions may 

 be clear. 



The Grande Faille de Bagnaud is distinct at la Puech, the summit of 

 the road from Firmy to Cransac, about a mile east from the latter town ; 

 but southeast from la Puech it could not be traced, as exposures thence to 

 Auzits are indefinite; northward, however, it seems to be crossed by the 

 Riou Banel and its existence is highly probable thence to Eiou Mort at 

 Decazeville, where a well-marked fault exists. Northeast from Cransac, 

 the throw is sufficient to bring the Campagnac and Bourran beds to nearly 

 the same level. 



An east and west fault passes from the Bagnaud fault to the eastern 

 border; it will be spoken of as the Firmy fault. A third fault is very 

 distinct between the outcrops of the Bourran bed, northwest from Cran- 

 sac. A fourth was recognized by Bergeron, Jardel and Picandet in the 

 south-central part of the basin and designated as the Grande Faille de 

 Lugan. These four are the only ones with extensive throw, but the mine 

 maps and the decouvertes exhibit many others of 20 to 50 feet, some of 

 them very complicated. These, however, though numerous and perplex- 

 ing to the mining engineers, need no consideration here. 



The writer's detailed observations were made in the space between the 

 Eiou Mort and the Euisseau de I'Enne, where the coal beds have their 

 chief development; but the southeast corner as well as the area north 

 from Eiou Mort was visited and the relations were made out. No studies 

 were attempted along the southern border or in the southwest corner, 

 where investigations by Bergeron, Jardel and Picandet have made the 

 conditions so clear that nothing except visual familiarity with the phe- 

 nomena could be gained by an examination. For the localities not vis- 

 ited, citations will be made from the memoir by those students. 



