STEVENSON, COAL BASIN OF DECAZEVILLE, FRANCE 247 



toid gneiss, in which is implanted a boss of serpentine. These rocks are 

 well shown in the valley of Eiou Mort, being reached at only a few rods 

 from the stream. Opposite the village of Firmy, one finds Permian beds^ 

 which are the boundary thence for four miles to the end of the ridge 

 overlooking Auzits, where they rest on the mica schist. From Auzits 

 southward and then westward, mica schist is probably the boundary rock, 

 though for nearly two thirds of the distance along the southern border, an 

 irregular line of more than six miles, it is covered by Jurassic beds. In 

 the southeast comer are some patches of microgranulite, whose relations 

 should be well fixed in mind, as fragments derived from those patches 

 gave the first positive clue to the mode in which the basin was filled. 



One finds occasionally within the basin fragmentary areas of rocks 

 belonging to the boundary types. Two small patches of Jurassic remain 

 in the southwest at one and three miles from the outcrop. Permian is 

 present in the region south from Decazeville to beyond the Euisseau de 

 I'Enne. Midway along the southern boundary, some bosses of a "roche 

 porphyrique alteree" project into the Coal Measures, and a similar rock 

 appears in small quantity at several places beyond the border of the basin. 

 These bosses are in line with islets of andesite and microgranulite, the 

 last of which is more than four miles from the southern boundary. 



Aside from these rocks, one finds indicated on the map a small area of 

 Coal Measures in the extreme southwest corner; another of less size on 

 the granite, and still another on the mica schist of the western boundary. 



DESCEIPTION OF THE BASIN" 



To determine the stratigraphical relations from surface exposures 

 would be well nigh impossible. The region has suffered greatly from ero- 

 sion, but the slopes of the hills, though usually rather steep, rarely give 

 any but fragmentary exposures; while side cuttings on the well-graded 

 roads are too widely separated to yield satisfactory information respecting 

 an area which is closely folded and is slashed by faults. The great open 

 workings, termed "decouvertes," and the extensive underground develop- 

 ments have provided material for determination of the structure. The 

 conditions are far less simple than in les Pegauds of Commentry, where 

 the coal accumulated in a wholly insignificant area. 



The cutting to which the present topography is due was determined 

 by the Lot Eiver, which crosses the north end by a tortuous course. The 

 Eiou Mort, Euisseau Banel, Euisseau de I'Enne and the Eiou Vieux, 

 draining the basin, unite beyond the western boundary near Yiviez and 

 enter the Lot Eiver within three miles. The course of that river within 

 the basin seems to have some relation with the distribution of andesite. 



