I9I2.] STEVENSON— THE FORMATION OF COAL BEDS. 551 



inconceivably great results. Apparently the first distinct formula- 

 tion of the new presentation in America was made simultaneously 

 by Barrell and Grabau/^* each of whom utilized phenomena of the 

 Appalachian basin in illustration. Barrell's elaborate memoir dis- 

 cusses the subject in all its phases and merits careful study. He 

 exhibits clearly the important part which river plains played in the 

 Appalachian history down to the close of the Carboniferous. Grabau 

 lays stress on the progressive overlap away from the source of 

 supply, which, when associated with other facts, becomes an impor- 

 tant element of the argument. 



Study of the facts presented on the pages of this memoir has 

 forced the writer to a conclusion very different from that hoped for 

 when this investigation was begun. 



The widespread horizontality of the Coal Measures deposits, 

 coarse and fine alike, recalls conditions observed on the Siberian 

 Steppe and other river regions. The folding of the beds proceeded 

 from a common cause, lateral pressure applied at the east. The 

 violence of plication decreases with notable regularity toward the 

 west, until in western Pennsylvania and in Ohio, along a line of 

 more than lOO miles, the folds become so gentle that they can be 

 traced only by close study. Dips of more than one degree are 

 unusual, while at times and for considerable distances the dip is 

 barely one half of a degree. The same condition exists in a great 

 part of West Virginia. The regular decrease in steepness of the 

 folds leads to the belief that originally the beds were, to all intents, 

 horizontal throughout the basin, the condition being that observed 

 on the great river plains of comparable extent. The rare occur- 

 rence of driftwood in the widespread deposits is characteristic not 

 only of the Coal Measures but also of vast river deposits, those of 

 the Amazon, as described by Brown, and of the Ganges as described 

 by Medlicott and Lyell. The long narrow areas of coarse to pebbly 

 sandstone, often with driftwood, recall the filled valleys of the 

 Sierra, described by LeConte, as well as filled deserted bows on the 



^^*J. Barrell, "Relative Importance of Continental, Littoral and Marine 

 Sedimentation," Journ. of Geol., Vol. XIV.. 1906, pp. 22)7, 338, 539-541 ; A. W. 

 Grabau, " Types of Sedimentary Overlap," Bull. Geol. Soc. Amer., Vol. 17, 

 1906, pp. 635, 636. 



PROC. AMER. PHIL. SOC, LI. 207 I, PRINTED DEC. 17, I9I2. 



