278 ANNALS NEW YORK ACADEMY OF SCIENCES 



represented at most by a few feet. But the interval between the Boiirran 

 coal and the coarse rocks above is great, nowhere less than 150 feet, filled 

 with shale and mostly fine-grained sandstone, while the overlying coarser 

 sandstones are only finely conglomeratic, as though composed of older 

 deposits worked over. 



Evidence derived from the character of the transported material leaves 

 no room for doubt that the streams were short. The quantity of material 

 transported by them leads to equally positive conclusions. The extreme 

 thickness of the Auzits system approximates 1800 feet, but this measure- 

 ment is made along the supposed line of the Haute Serre stream. The 

 basal deposit, with an extreme thickness of 600 feet, is very coarse, its 

 fragments are subangular and the exposed area is somewhat less than two 

 square miles. The general character suggests that the material is very 

 near its original source and that it is largely of subaerial origin. It must 

 decrease very rapidly in all directions, especially toward the north, and 

 the Soulier coal bed, if it exist, should be very near the Archean beyond 

 Eiou Vieux. The Auzits area increased with the newer beds, so that at 

 the close, its deposits must have covered the eastern half of the depres- 

 sion. One seems to be justified in assigning to this system an area of 

 six square miles with an average thickness of 1000 feet and a content of 

 somewhat more than a cubic mile. For this considerable mass, one must 

 look in great part to the three streams at the south, since the exposed 

 area is in their region and the recognized materials could have come only 

 from rocks cut by them. If those streams by the end of the Auzits had 

 dug valleys such as one sees in the upper reaches of the Enne or Eiou 

 Vieux, the removed material would suffice for the whole deposit. The 

 Campagnac system covered the eastern half of the basin, not less than 15 

 square miles in area, with an average thickness of say 600 feet. The 

 content would be somewhat less than two cubic miles, to which all streams 

 contributed. The Bourran system covered apparently the whole area, 

 30 square miles, with a thickness of say 450 feet and a content of two 

 and one half cubic miles, to which all streams contributed, not only those 

 whose work has been recognized, but also others of less importance. 



These estimates may be open to charge of exaggeration, but they have 

 been made liberally. A calculation of cubical content of the deposits 

 suffices to make wholly clear that the whole work of removal and distribu- 

 tion could have been done by streams, gradually lengthening and deepen- 

 ing their ways until at the close of the Coal Measures the streams and 

 valleys in the schists resembled in size and extent those now existing in 

 the Decazeville basin. 



