I9I3.] STEVENSON— FORMATION OF COAL BEDS. 133 



can be made only in a considerable body of water — itself a concep- 

 tion which is in great need of proof. But one must concede that it 

 involves many and serious difficulties in its application to small 

 areas, such as the Commentry and Loire basins, and still greater 

 difficulties when larger areas are considered ; the more so when one 

 remembers the proposition presented by some eminent men, that a 

 bed of coal may be the product of a single flood. 



Taking the Commentry basin as typical for small areas, one 

 finds that coal accumulation began there only after not less than 500 

 meters of inorganic deposits had been laid down and a considerable 

 part of the area had been converted into land. The two ponds, 

 Pegauds and Ferrieres, were separated by the barren zone of 

 ]\Iontassiege, debris from the Bourrus torrent. The areas of those 

 ponds were perhaps rather more than 2,000 and 1,000 acres re- 

 spectively. The floods leading to formation of the great coal beds 

 on the north shore of those ponds were extreme; trees were carried 

 down and deposited with the sands in all directions, erect, inclined, 

 prostrate and, in at least one instance, upside down. The vegetable 

 cover was stripped from the drainage area and the whole mass was 

 swept along narrow gorges through which the torrential streams 

 flowed. This conception of the violence is not excessive; nothing 

 less could do the work; for one must remember that the streams 

 were still young, their gorges had been cut in granite and gneiss ; 

 the course must have been tortuous and the beds irregular, with 

 shoals and rapids. When this vast mass of debris reached the 

 water-basins, deep or shallow, they would be churned up by the 

 flood's mad rush for the outlet, through which the water would pour 

 with the force of a lake Bagne debacle, carrying with it the finer and 

 much of the coarser materials. There could be no selection under 

 the influence of. gravity. The Banc des Roseaux, dividing the 

 Grande Couche, contains trees in great abundance, supposed to have 

 been brought down by the streams ; no selection was there, for the 

 deposit is not along the main stream line of either Bourrus or 

 Colombier, but in the supposed bay between the deltas. It might 

 be suggested that the flood exercised its selective power before be- 

 ginning: the downward course. 



