74 STEVENSON— FORMATION OF COAL BEDS. [April 21. 



converted into ulmic material, the lower part of the deposit becoming 

 a blackish paste. Detached heaps of leaves, peripheral sheaths of 

 ferns, cortex of Sicjillaria, Cordaitcs, etc., obstructed places at foot 

 of slopes and awaited only the passage of waters in order to abandon 

 to them the great mass of material in various stages of decomposi- 

 tion. This vegetable pulp is the amorphous gangue in which one 

 finds the barks and leaves. But it is no longer in place. It shows 

 evidence of having been suspended in water; the condition of the 

 fragments shows that they have been subjected to frequent and 

 energetic friction. By what mechanism was this transport effected? 



Grand' Eury thought that the waters of great rains sweeping 

 down the slopes drew the vegetable detritus into lagoons — such 

 waters were limpid. At other times the streams carried muddy 

 water with sand and clay giving sandstone and shale. Thus was 

 explained the alternation of coal with other rocks. But de Lapparent 

 cannot understand this selective process — the conditions are unlike 

 those of the present day. The delta theory of Fayol is preferable 

 and it applies perfectly to the lacustrian basins of central France. 

 It is no mere hypothesis, but the result of long, painstaking observa- 

 tion in the great open quarries of Commentry. More, Fayol made 

 experiments which proved that the conditions were such as must be 

 due to delta formation. 



The cause was gained and it remained only to answer objections 

 offered by adherents to the old theory. The presence of vertical 

 trunks was shown to be not only not inconsistent but rather consistent 

 with the theory. And this was the most important objection. The 

 presence of Stigmaria in the underclay is no objection. Those are 

 rhizomas capable of giving origin to Sigillaria : when swept by tor- 

 rential currents, they were drawn into the deltas, where being heavier 

 they would pass to the bottom of the mass which was to become coal. 

 The delta theory is full of important consequences. There is no 

 further need of numerous and complicated movements of the crust. 

 The beds have Ijeen deposited one on the other as sediments on the 

 surface of a submerged dejection cone. If complete stability of the 

 surface be one of the conditions of the phenomenon, there is at least 

 no a priori reason to ])ut it in doulit ; as the beds had to be deposited 



74 



