254 



ASHLEY — GEOLOGY OF ARKANSAS. 



[May 13, 



The Western Sheet. — The western half of the area offered some- 

 what better facilities for working out the structure, due principally 

 to the existence of four large streams running across the folds from 

 north to south. These streams are rapid, and frequently they cut 

 their way through the ridges in deep, steep-banked gorges for long 

 distances. Rocky cliffs seldom occur, but the shallow creek bottoms 

 afford many exposures of rocks. Between these streams exposures 

 are as scarce as further east. 



On the other hand the topography is of much service in suggest- 

 ing structure. It is through the suggestions thus given by the 

 topography that the connections between the exposures of axes 

 have been worked out. 



In townships 3 and 4 S. the strike of the folds is east-west or a 

 little north of west. In 5 S. the strike is nearly always about due 

 east-west. In 6 S. the strike is a little south of west, becoming due 

 west as the Indian Territory line is approached. 

 In 7 S. the slightly south of west strike is main- 

 tained. 



Thus it will be noticed that as the Indian Terri- 

 tory line is approached the fold tends to spread 

 out like a partly opened fan. This results in the 

 folds becoming more open toward the west. While 

 the strata are closely lolded or overturned on the 

 Little Missouri and West Saline rivers, on the Cos- 

 satot they present more simple anticlines, and still 

 further west, on the Rolling Fork, simple anticlines 

 and lower dips are still more prevalent. This is 

 especially true of the southern half of the region. 

 Where the dotted lines on the map suggest con- 

 tinuity of the axes, it is not necessarily implied that 

 the anticlines are strictly continuous ; as the com- 

 plete structure, if known, might show two or more 

 anticlines where only one is indicated, and these 

 might be strung along in a line or be slightly out of 

 line with the ends overlapping or running past each 

 other. 



Structural Types. 



a 



Fig. 2.— Col- 

 umnar section of 

 Paleozoic rocks 

 south of the 

 Ouachita moun- 

 tains. 



As introductory to tracing out the anticlines and 

 synclines in the next chapter, it may be well to 



