228 



A. WINSLOW GEOLOGY OF WESTERN ARKANSAS. 



the coals of the valley of Arkansas river. The results of one of these sec- 

 tions are embodied in the generalized section, figure 1, and the total thickness 

 of the formations exposed within the area described is there approximately 

 shown. Further, a study, by Mr. G. D. Harris, of the flora of certain coal 

 beds on the Arkansas river, in the vicinity of Russell ville, led to the con- 

 clusion that they represent horizons above the conglomerate. On strati- 

 graphic grounds these latter beds are placed many hundreds of feet beneath 

 the uppermost beds represented farther west in the state : hence we have 

 reason for assigning to these latter beds a position well up in the Coal 

 Measures. 



The Geotectonic Geology. 



Character and Distribution of the Flexures. — In illustration of the char- 

 acter of the flexures of this area, figures 1, 2, 3, 4, 5 and 6 are presented. 

 Figure 1 is a generalized cross-section through the Boston mountains and 



Figure 2.— Cross-Section through the Poteau Mountains. 



Scale, horizontal and vertical, 1.6 miles = 1 inch. Looking westward. Showing the steeper dips 

 northward. 



the Arkansas river valley. It illustrates the diminution in intensity of flex- 

 ing from south to north. This section is constructed along a line running 

 in a direction nearly due north and south, at right angles to the axes of flex- 

 ures, which are invariably east and west lines, exact or closely approximate. 

 From the Poteau mountains northward the flexures are seen first to be 

 intense, and then to diminish until they terminate in the grand monocline 

 of the Boston mountains. 



Figure 3.— Cross-Section through the Washburn Anticline. 



Scale, horizontal and vertical, 1.25 mile = 1 inch. Looking westward. Showing overturned fold 

 and fault, indicating lateral movement from the south. 



Figure 2 is a section constructed on equal horizontal and vertical scales 

 across the Poteau mountains. It illustrates not only the excessive dips of 

 the south, but also the general fact of the greater inclination of northward 

 dips over southward dips. 



The last condition is also illustrated by figures 3 and 4 : the former repre- 



