I9I3.J STEVENSON— FORMATION OF COAL BEDS. 129 



from slaty admixture as to suggest that, during its formation, the 

 streams brought into the area practically no inorganic material. It 

 rests on the Banc des Roseaux, a sandy deposit literally crowded 

 with stems and trunks, and extending apparently no farther than the 

 coal in any direction. The purity of the coal shows that the whole 

 mass was brought down at once, and it is at the head of the recess 

 between the Bourrus and Colombier deltas — where neither it nor 

 the sandy bed below should be. 



A flood, so terrific as to sweep such a mass of vegetation from 

 the little drainage area, could not be confined to the head waters of 

 the Bourrus and Colombier; the other short streams between them 

 would also be in flood, pouring their great contribution of water into 

 the pond. There could not be any eddying; the whole surface of 

 the water would be dashing with its load toward the outlet. If that 

 were blocked, much of the deposit would be made along the southern 

 border. But, even conceding that the trees were not deposited 

 there, one must not forget that floods of the supposed violence are 

 of brief duration and that floating wood remains very long time 

 before becoming waterlogged. The surface movement would be 

 steadily toward the outlet ; there is no conceivable manner whereby 

 the enormous mass of trees could be pushed against the current so 

 as to be deposited at the head of the pond, where the water was too 

 shallow to float the raft not less than 150 feet thick. But aside from 

 this, the coal is not where it should be. According to the law of 

 deposit on a deeply submerged delta cone, coal should be found 

 crossing the cone in curved lines and it should thicken in the direc- 

 tion of the finer sediments. But there is no coal curving across the 

 Bourrus delta ; the coal of the Grande Couche disappears in the 

 direction of finer sediments. 



Conditions in the Decazeville basin bear no resemblance to those 

 in the Commentry basin. The relation of the coal beds to old river 

 courses and the variations in thickness are wholly different. The 

 theory that coal beds were deposited on the slopes of submerged 

 delta cones does not account for the conditions observed in those 

 basins ; Grand'Eury and Gruner found that theory inapplicable to 



PROC. AMER. PHIL. SOC, LII. 2o8 I, PRINTED MA.Y l6, I9I3. 



