I9II.] STEVENSON— FORMATION OF COAL BEDS. 71 



sitit after the manner of swamps, he thinks a period of 800,000 years 

 would be required. 



Fayol's delta theory, then, is that the deep lake was filled gradually 

 with material carried down by the streams ; that this material was 

 deposited according to its gravity, fine clay and vegetable matter 

 being regarded as equivalents ; the arrangement being that observed 

 in deltas. It differs from the theory offered by Jukes by adding the 

 suggestion of great original depth of the basin, a conception against 

 which V. Gumbel had argued a number of years before. 



The record of the summer meeting of the Geological Society was 

 issued as a separate'- and it contains the discussions by several mem- 

 bers. The doctrine as enunciated by Fayol was regarded by Busquet 

 as applicable to the basin of Decize, by Nougarede as supported by 

 much observed in the basin of Epinac, and by Bergeron as explaining 

 the conditions observed at Grassesac and Decazeville. 



Renevier'^ was not prepared to give assent to the doctrine and he 

 suggested some grounds for hesitation. Vegetable materials in sus- 

 pension are equivalent to fine mineral debris. If the coal beds were 

 formed, as Fayol thinks, by the sweeping ofT of vegetable debris from 

 the land and its deposition on the surface of the delta, that debris 

 should accumulate on the border of the dejection cone, in the more 

 tranquil waters, so that the deposit should have only a gentle original 

 slope. But the great bed of Commentry has an extreme dip of 50 

 degrees, the same with that of the beds which accompany it. He 

 regards these dips as impossible in a cone of dejection and suggests 

 other modes of accounting for them. He maintained that the phe- 

 nomena indicate, in part at least, the agency of marshy or semi- 

 aquatic vegetation. Even the great thickness of the Grande Couche 

 seems to him an argument in favor of vegetation in place, receiving 

 increment brought in from the neighboring forests. 



Delafond'* was inclined to question the applicability of the 

 doctrine without modification to the basins of the Saone-et-Loire 

 (those of Autun, Blanzy and Creusot). Fayol conceived the exist- 

 ence, before the coal deposition, of a deep depression transformed 



" " Reunion extraordinaire dans rAllier," Bull. Soc. Geol. dc France, 3""" 

 Ser., XVI., 1890. 



" E. Renevier, " Reunion, etc.," pp. yy, 78. 

 "F. Delafond, "Reunion, etc.," pp. 73-78. 



71 



