STEVENSON, COAL BASIN OF DECAZEVILLE, FRANCE 391 



One may not appeal here to Fayol's ingenious explanation of condi- 

 tions observed at Commentry, for those conditions do not exist in the 

 Decazeville basin. In the former basin, the bifurcation of the Grande 

 Couche toward the shoreline is regarded as evidence that while the delta 

 advanced, coal was deposited continuously in the basin beyond, but the 

 deposition was interrupted on the delta slope; so that several thin beds, 

 widely separated at the shore might be one far out in the basin. That 

 explanation is not available for Decazeville, for no such relation exists 

 Ijetween the coal beds there, the greatest intervals between them being in 

 the central and eastern parts of the basin. 



Whatever may or may not be the worth of the Fayol doctrine respect- 

 ing the formation of coal beds as applied to other localities, the fact 

 remains that the fundamental requirements of that doctrine do not exist 

 in the Decazeville region. The doctrine is wholly exact when applied to 

 the accumulation of inorganic materials, but one must look elsewhere for 

 an explanation accounting for the accumulation of the coal beds, an ex- 

 planation consistent with phenomena known to have existed at many 

 l^eriods in the earth's history and known to be existing now. And this is 

 found only in the doctrine of origin in situ. 



HISTORY OF THE DECAZEVILLE BASIN 



In the later portion of the Carboniferous, a triangular block of schist 

 and coarse granite was dropped within the three limiting faults, with its 

 surface sloping gently toward the southeast, thus giving a slight depres- 

 sion, in form of a gaping fault. Midway on the eastern side, near the 

 present village of Firmy, there seems to have been a valley, eroded by a 

 preexisting stream, and with floor still below that of the depressed area. 

 The vertical displacement, small at first, was sufficient to disturb the 

 drainage, for streams entering from the south evidently originated at 

 this time. Water from all sides escaped through the outlet near Firmy. 

 while detritus was dropped on the borders. The especial line of weak- 

 ness was along the southeastern side, where subsidence continued until 

 the floor sank beneath the outlet valley and water accumulated to form a 

 pond with an area of several square miles. The little streams carried 

 their loads into the pond, filled it and flowed across the newly made land. 

 The finer materials, spread during flood time over this area, converted it 

 into a muddy flat, of which plants took possession. During extremely 

 slow subsidence, vegetable debris accumulated in the swamp to form the 

 Soulier-Abiracs coal bed. Conditions favoring such growth and accumu- 

 lation obtained first where the Haute Sorre and Lugan deposits were con- 

 fluent, and thence they extended slowlv in each direction. 



