C)60 DRAKE — THE GEOLOGY OF INDIAN TERRITORY. [Sept. 3, 



until the deposited beds were subject to slight erosion before the 

 following subsidence began and the sand and grit deposits laid 

 down over them. The continuity of the fauna and the small amount 

 of overlapping in these deposits could, however, allow only a slight 

 break in deposition. 



Coal Measures. 



The Coal Measures of the Indian Territory and Oklahoma are a 

 direct continuation of the Kansas, the Arkansas and apparently the 

 Texas Coal Measures. The southward extension of the Coal Mea- 

 sures of Kansas enters the Indian Territory in a belt sixty- 

 five miles wide, which extends from about ten miles west of the 

 northeast corner of the Territory to near the northwest corner. The 

 western limit of this belt through the Territory bears about io° west 

 of south throughout the area studied. The eastern limit running 

 southward from the Kansas-Indian Territory line extends south 

 40° W. for a distance of forty miles, then rims nearly south for fifty 

 miles and then with a gentle southward curve and zigzag line ex- 

 tends eastward into Arkansas. The belt through the Territory, 

 therefore, at first contracts from the eastern side for a distance of 

 nearly one hundred miles, then rapidly widens on the eastern side 

 so that the Coal Measures in the territory studied, roughly covers an 

 L-shaped area. The southward continuation of the Coal Measures 

 into Texas is broken in the southern part of the Indian Territory by 

 the overlapping of Cretaceous deposits. 



Structure. — The Coal Measures lie in the three structural and to- 

 pographic groups previously mentioned. The horizontally uplifted 

 plateau, or Ozark type, includes the larger part of the Coal Measures 

 lying between the southern boundary of the Lower Carboniferous 

 area and the northern boundary of the Arkansas river valley. The 

 area of the folded beds, or Ouachita type of structure, lies princi- 

 pally south of the Arkansas river and east of a line connecting the 

 mouth of the Canadian river, Brooken, and a point about seven 

 miles west of McAlester. The remaining and by far greater part 

 of the Coal Measures in the area under discussion belongs to the 

 Prairie Plains region, and consists of gently westward and north- 

 westward dipping strata. 



Stratigraphy. — With the possible exception of slight uncomformi- 

 ties produced by overlapping of the basal beds of the Lower Coal 

 Measures, there seems to be no break in the stratigraphy from Lower 



