274 ANNALS NEW YORK ACADEMY OF SCIENCES 



The limiting fault at the west, recognized by Bergeron' in 1888, is 

 distinct from the southern border northward, passing on the west side of 

 the granite area, but making an angle at Eiou Mort, whence it is trace- 

 able to its disappearance under post-Carboniferous rocks at the north. 

 On the eastern side a well-defined fault extends northwardly to beyond 

 Eiou Mort, east from Firmy; and the map by Bergeron, Jardel and 

 Picandet makes it very probable that a fault continues from Eiou Mort 

 to the northern part of the basin, as was suggested long ago by Bergeron. 

 Whether or not the basin was limited by a fault at the south cannot be 

 determined from the observations now available; but the existence of 

 such a fault seems to be more than probable. Bergeron's sketch-map 

 marked it as extending from the western boundary near Valzergues south- 

 eastward to the mica schists on the opposite side, but the map in the later 

 memoir does not show it, as its place along the greater part of the south- 

 em border is concealed by Jurassic beds. The basin owes its origin to 

 these limiting faults, along which as lines of weakness those adjustments 

 were made which, by changing the relative levels, made possible the depo- 

 sition of a thick mass of Coal Measures. They may have been involved 

 in the final changes, causing the present complicated structure, but their 

 share in them was merely subordinate. The Permian on the ridge road 

 above Auzits appears to be afl^ected very slightly by the limiting fault. 



The area of deposit was confined at first almost wholly to the south- 

 east corner, but it expanded gradually until, at the close of the Campag- 

 nac period, it embraced almost the whole of the eastern half and a con- 

 siderable space along the southern border. During the Bourran, the 

 whole of the present area received deposits. The studies by Bergeron, 

 Jardel and Picandet leave no doubt respecting conditions in the western 

 part of the basin during the Bourran, and the writer adds his testimony 

 in corroboration for localities examined by him. There is no reason 

 whatever to believe that the basin was occupied at any time by a body of 

 deep water; for a long time a great part of the area was exposed to sub- 

 aerial action. The evidence is positive. 



Bergeron, Jardel and Picandet report the occurrence near Antaig- 

 nargues of a mica-schist breccia, composed of great blocks, which they 

 seem inclined to regard as part of a delta, therefore as deposited by run- 

 ning water. This explanation of the origin is open to question. The 

 vast size of the angular blocks would lead one to think rather of sub- 

 aerial disintegration as the causal agent. Somewhat similar deposits are 

 described from the southeastern corner. A small area of about eight 



^ Reunion, etc., dans I'Anier, p. 82. 



