218 M. Du Boec on the 



Sdly. The coal basin of the South, or of the Tarn, which 

 belongs to a limestone formation. 



Of these three coal basins I shall only here speak of the 

 second, that of the Aveyron. 



Its general direction is from E. to W. and it runs nearly 

 parallel with the river Aveyron, constantly following the 

 left bank of this river, without ever passing over io the right 

 side, excepting on its western limit, (very near the town of 

 Rodez). 



The two towns of Rodez and Severac-le-Chateau may be 

 considered as the two extreme points of the coal formation, 

 which is thus about 36 kilometres [about 27-1. miles] long 

 from E. to W. while its breadth from N. to S. is variable, 

 never exceeding 3 kilometres [about 2^ miles], and being 

 most commonly much less. 



The coal formation, beginning very near Rodez, the chief 

 town of the department, passes along the left bank of the 

 Aveyron, traversing successively the communes of Agen, 

 Laloubiere, Montrozier, Bertholene, Layssac, Severac- 

 I'Eglise, Gaillac, Recoules, and Laveruhe. Coal has been 

 found and worked in these diflFerent communes, with the 

 exception of those of Severac I'Eglise and Galliac, where 

 there has been found, not coal, but coal measure sandstone. 



The limits of this coal formation are, on the N. a vast 

 formation of secondary limestone which covers the sandstone, 

 and which forms a vast platform, named Causse, * which 

 occurs between the rivers Aveyron and Lot. The predomi- 

 nant rock is a true compact limestone, almost always shelly, 

 but very variable in its colour, structure, and hardness. Its 

 colour varies from yellow to dull white and grey ; it some- 

 times passes into argillaceous limestone ; at others it becomes 

 s6 schistose, that it is employed as roofing slate. 



The direction of the limestone beds is from E. to W. f 

 their inclination towards the S. is always slight, and it has 



* The word causse is a generic name for the limestone soils proper for 

 the cultivation of wheat, while the name segala is given to the mica slates 

 and gneiss, which scarcely produce any thing but rye. - 



