242 A. WINSLOW GEOLOGY OF WESTERN ARKANSAS. 



A valley of shales a few miles south of this offers opportunity for a shorten- 

 ing of the channel through easily corraded material ; yet the river cannot 

 escape from its inherited bondage between mountain walls. Another in- 

 stance is just above Dardanelle. The gorge here is only a few miles long, 

 but is particularly interesting in that it cuts straight across the point of a 

 sharp syncline ; a feature of flow of a decidedly antecedent character. 



Of monoclinal shifting of channels, there is abundant evidence in the even- 

 ness in slope of the sides of many monoclinal ridges. In some cases this slope 

 conforms exactly with the dip of the underlying sandstone, and in places this 

 sandstone is almost as bare as when left by the stream as the channel gradu- 

 ally shifted down the slope of the rock. 



The courses of the stream across the ridge systems are always nearly at 

 right angles, while they run lengthwise in the longitudinal valleys, thus illus- 

 tratiug the tendency of waterways to escape from hard strata and to abide 

 in soft, as indicated by Gilbert. 



Of backward headwater erosion most of the anticlines seem to furnish 

 evidence. The valley enclosed by Coops ridge seems indisputably a result of 

 this action. 



An interesting case of the readjustment of channels is presented by Petit 

 Jean creek along the Jennings hill syncline. The stream at one time evi- 

 dently followed the axis of the syncline, as is indicated by the succession of 

 notches along the line through the encircling ridges. From this central 

 channel it has evidently been diverted to the one it now occupies, north of 

 the monoclinal ridge, by the tapping action of a stream which flowed origi- 

 nally as a tributary in this valley of soft rock. 



