282 ANNALS NEW YORK ACADEMY OF SCIENCES 



was not divided by a main delta deposit, and it maintained its integrity 

 throughout, the area of deposit apparently increasing as time went on. 

 The coal making was not confined to petty areas, but the beds formed 

 practically continuous sheets over a great part of the surface, the Bour- 

 ran and Campagnac extending to the outlet at Firmy. In Commentry, 

 there is no coal on the delta of the Bourrus brook, the barren zone of 

 Montassiege, or even on the deltas of the Chamblet and Colombier 

 brooks, as defined by Fayol. Aside from some insignificant patches along 

 the northern border, one finds coal only in the recesses between the Mon- 

 tassiege and Colombier zones on one side and between Montassiege and 

 Chamblet on the other. But in the southeast corner of the Decazeville 

 basin, one finds the coal crossing the conjoined deposits of the Longuefort 

 and Haute Serre brooks — and this condition continued there throughout, 

 for the curved outcrops of the Soulier, Campagnac and Bourran beds are 

 shown crossing the area of stream deposit from Haute Serre to ^i^m5^ 

 One must bear in mind that the curved outcrops are no evidence of origi- 

 nal form or extent of those beds; they are due to erosion of a fold with 

 strong northward pitch. The distance from Haute Serre to Firmy is 

 about four miles. Farther north, the Campagnac bed crosses the area of 

 deposit as clearly as at the south. 



The contrast between Commentry and Decazeville is so great that the 

 delta theory as determined at Commentry would have to be modified in 

 important respects before becoming applicable to Decazeville. The 

 theory, as formulated by Fayol, may be summarized thus: 



The coal terrains have great analogies to present deltas ; both are composed 

 essentially of materials carried by streams of water ; the plant beds of deltas 

 are represented in the coal terrains by combustibles of plant origin. In the 

 coal terrains, as in deltas, the extent of the beds varies from a few square 

 meters to some thousands of square kilometers; the thickness varies from a 

 mere trace to several dozens of meters ; the size of the elements from the 

 finest grain to blocks of several cubic meters. At Commentry, a lake sur- 

 rounded by mountains was in the place now occupied by the Coal Measures. 

 Rain water gradually ate away the surrounding region, dug valleys and car- 

 ried to the lake pebbles, sand, mud and plants, which finally filled it ; these 

 are the materials which constituted the beds of conglomerate, sandstone, shale 

 and coal making up the Coal Measures. The lake of Commentry was nine 

 kilometers long by three wide and its greatest depth was about 800 meters. 

 The distribution of materials depends on their specific gravity or fineness, as 

 well as upon the condition of the water, whether quiet or agitated, into which 

 they are carried. The finer, lighter elements will be carried much farther 

 than the others before reaching the bottom." 



i»H. Fayol, "Reunion, etc.," pp. 14, 19, 13. 



