124 STEVENSON— FORMATION OF COAL BEDS. [April i8, 



coarse " Sperrgut " to pass over so as to form a coal bed in the basin, 

 it would be no longer a mere dam: it would be a deposit in the 

 channel-way, miles long, which would be impregnable against any 

 flood: the mighty debacle, which would sweep out the dam and all 

 accumulated material behind it, the '" Rollgut," to make a sandstone 

 and conglomerate deposit in the basin, is beyond the reach of 

 imagination. Being in a lowland, little above sea-level, there could 

 not be any such flood as Ochsenius conceives, since high water would 

 give only a comparatively harmless overflow. But at best, the 

 obstruction would cause the river to seek a new channel-way. That 

 was the effect of the Red river raft ; the Sudd of the Nile, overturned 

 trees blocking the channel of the Bermejo in Paraguay, obstructions 

 along the upper Mississippi do the same thing; they are not swept 

 out by the high floods, they merely cause diversion of the stream. 

 The breaking of levees along the Mississippi has no bearing on the 

 matter. Those structures have a moderate base in comparison with 

 their height, whereas the barricade, after centuries of accumulation, 

 would be only a few feet high and miles long. 



Jukes saw in the Coal Measures of the South Staffordshire field 

 deposits resembling those on a submerged delta cone; his arguments 

 have been presented on an earlier page. Almost a quarter of a 

 century later, Fayol, after long study of the Commentry coal basin, 

 reached similar conclusions, which, in 1888, he presented in such 

 admirable form, with such skilfull attention to detail and with such 

 apparent grasp of all the features and possibilities, that his concep- 

 tion w^on instant approval from many eminent geologists in all lands 

 and it was accepted as a final explanation of phenomena in the 

 limnic basins of central France. This " Delta theory " merits care- 

 ful consideration. 



According to Fayol, the basin of Commentry was occupied by a 

 lake, 9 kilometers long and 3 kilometers wide, with greatest depth 

 of 800 meters and with an outlet on the southern border. Rain 

 water ate away the surrounding mountainous region and the trans- 

 ported materials are those composing the beds of conglomerate 

 sandstone, shale and coal now filling the basin. The distribution of 

 those materials was determined by their specific gravity or their 



