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



the Loire basin. Its author did not assert that it could be utihzed 

 to explain conditions in paralic areas, but he evidently expected to 

 find support for it in those also. It is fully evident that it has no 

 application whatever to the Appalachian basin, where the rocks 

 were deposited in horizontal condition. Even now, they are almost 

 horizontal in areas of many thousands of square miles within Ohio, 

 West Virginia and Pennsylvania, where for long distances the dip 

 is from one fourth to one half degree — and this dip is not original, 

 for the region was affected by the Appalachian revolution and the 

 beds were flexed. One nowhere finds any evidence of the sub- 

 merged, steeply dipping beds of a delta; but the thousands of oil- 

 well records show conformity throughout the Coal Measures column 

 — aside from the variation due to local conditions or to widespread 

 differential subsidence. 



The term " Delta theory " is an unfortunate misnomer, 

 " Delta," as ordinarily understood, designates not merely the sub- 

 merged cone but also and chiefly the horizontal, alluvial deposits, 

 and it at once suggests conditions observed in the lower reaches of 

 great rivers, where the neptunian beds have very gentle slope. But 

 this doctrine concerns only deposits made in small bodies of water 

 by short torrential streams. The formation of a cone, such as the 

 doctrine recjuires, would be possible only if the water were very deep 

 and the bounding wall precipitous where the streams enter. There 

 is no "evidence that the conditions existed. No fault is known on 

 the northerly side, but a limiting fault is indicated on the southerly 

 side of the Commentry basin. There may have been important 

 accumulations of water, at times, due to blocking of the exit or to 

 depression along the fault, but such disturbances could have been of 

 only brief duration. The conditions at Commentry resemble very 

 much those observed along the Upper Rhone, and the writer is in- 

 clined to regard the " deltas " of the Bourrus and Colombier as 

 alluvial fans. 



Some of the " deltas " in the Decazeville basin have all the char- 

 acteristics of alluvial fans and the deposits show distinctly the 

 selective action of running water; but there are others which are not 

 due to stream action. The great granite conglomerates, with huge 



