i^yy.] 



DRAKE — THE GEOLOGY OF IXDIAX TERRITORY. 



365 



south of the Arkansas river. The rocks exposed along this anti- 

 ch'ne are mainly sandy clay shales north of Bokoshe, and massive 

 and flaggy sandstones east and west of Milton. The sandstones 

 one mile south of Bokoshe are highly micaceous and often smooth- 

 surfaced flags. About two thousand feet of Lower Coal Measures 

 rocks are exposed on either side of the anticline in this locality. 



In the Backbone mountain area of the Lower Coal Measures the 

 beds are massive sandstones and thick gray arenaceous clay shales. 

 The sandstone beds are from about thirty to five hundred feet in 

 thickness and the interbedded shales are from eight hundred to 

 thirteen hundred feet in thickness. The structure of the Backbone 

 ridges that best account for the observed facts is shown in Sees. 5, 

 6 and 7, PL VI and in PI. I. This overthrown anticline is faulted 



Plate VI. 



Through Ta.rn\er 



Seetioa 





Sections across the Backbone anticline. 



ection Jio S 



along the north side of the overthrow. The faulting runs westward 

 from Arkansas almost to the western end of the mountains, where it 

 ends rather suddenly. With the gradual lessening of the faulting 

 toward the west the strata on the north side of the fault line in- 

 crease in dip as they approach the axes of the anticlinal folds. 

 The thickness of strata exposed in this area, on either side of the 

 anticline, is a little over twenty-five hundred feet. The Lower 

 Coal Measures in the southeastern part of the field show very little 



