STEVENSON, COAL BASIN OF DECAZEVILLE, FRANCE 261 



bed. In this the dip of at least 30 degrees is ignored. Apparently, the 

 interval between the coal beds is between 750 and 800 feet along the 

 middle line of the basin and decreases toward the west. 



A stream entering at the southwest near Valzergues is believed by Ber- 

 geron, Jardel and Picandet to have begun its work during the Campagnac 

 period. They refer to the agency of this stream an isolated area of 

 granite conglomerate south from Valzergues, covering about 30 hectares 

 and resting on mica schist. It consists of granite blocks, four to five 

 meters in diameter, with rounded angles, and the intervals are filled with 

 granitic sand rich in feldspar. They think that the great size of the 

 blocks proves that they had been carried only a short distance. Farther 

 north is a conglomerate of mica schist and granite, also resting on mica 

 schist and succeeded by sandstones and shales containing some thin coal 

 beds, which are thought to be older than the Bourran system. 



The Bourran system of Bergeron. — Prior to the close of the Campag- 

 nac system, streams bringing noteworthy loads of detritus came almost 

 wholly from the south and the northeast, as proved by fragments inclosed 

 in the deposits. The outlet of the basin is supposed by Bergeron, Jardel 

 and 'Picandet to have been near Firmy, where those observers found a 

 commingling of materials from the north and the south. There is every 

 reason to accept this conclusion as correct. During the long period of 

 the Auzits and Campagnac systems, the western part of the basin received 

 little material, for except in the extreme southwest comer, there is hardly 

 anything on that side which can be recognized as certainly older than the 

 Bourran. The Lugan and Valzergues seem to have been important dur- 

 ing the formation of the earlier Bourran deposits ; and another, entering 

 from the west near the present Moulin du Faux, is supposed to have be- 

 come efficient at the beginning of the Bourran. 



The earliest deposit, as described by Bergeron, Jardel and Picandet, is 

 a conglomerate formed ever3rwhere of -enormous granite blocks, whose 

 "colossal dimensions" are seen as one goes from the Eiou Vieux up to 

 the hamlet of Faux. Some of them measure "10 metres cubes." The 

 intervals are filled with granitic sand, and blocks of granulite are seen 

 occasionally. This "granite conglomerate" is followed readily south- 

 ward for three miles, to near Montbazens, the blocks becoming smaller, 

 though still of great size. An insignificant outlier remains north from 

 Faux on the granite itself. The "granite conglomerate" is succeeded by 

 a mica schist-microgranulite conglomerate, derived in chief part from 

 the south ; and this in turn is succeeded by sandstones and shales with 

 some coal beds, most of which are too thin to repay working. This whole 

 series is referred by its describers to the Bourran system. Its rocks were 

 not examined by the writer. 



