17.] 



DRAKE — THE GEOLOGY OF INDIAN TERRITORY. 373 



to as the Choctaw coal field, ^ since this term has been applied to 

 that area by Dr. H. M. Chance. 



Stratigraphy.— T\\Q beds of this group consist of shales, sand- 

 stones, coals and limestones. The shales comprise the larger part 

 of the strata, but sandstones are very abundant, especially in the 

 southern part of the field, while limestone beds are confined to the 

 northern part. The workable coals are thicker in the southern 

 region, but extend throughout the entire area. The group is thick- 

 est in the southeastern part of the field and thinnest in the northern 

 part. The decrease in thickness appears to run regularly to the 

 westward and northward. The most constant and easily recogniz- 

 able horizons in this division are the coal beds. Three of these 

 are thick enough over most of the field to work. Other thin beds 

 occur locally, and one in particular that lies about one hundred feet 

 above the central coal bed extends almost regularly throughout the 

 field where its horizon occurs. The lowest workable coal varies 

 in thickness from one and a half to six feet ; this is the coal 

 that Dr. H. M. Chance named the Grady coal.' It proves to 

 be, without any reasonable doubt, the same bed as the one worked 

 at Huntington, Jenny Lind, Hackett and several other places in 

 Arkansas. 



The next higher workable coal is the McAlester bed, which 

 varies in thickness from about one and a half to four feet. The 

 highest workable bed is the Mayberry coal, which also varies in 

 thickness from one and a half to four feet. These three coal beds 

 apparently extend throughout the entire area of the Cavaniol group, 

 but north of the Canadian river there are four coal beds that are 

 worked locally. These four beds were not studied in enough detail 

 to correlate them throughout. The outcrops and stratigraphy noted 

 in different sections across the group give some suggestions of cor- 

 relation, as maybe seen in Pis. I and VIII. 



The following table shows a rough estimate of the distance 

 between the coal beds at different places in the Choctaw coal 

 field: 



1 Trans. Am. Inst. Min. Eng., Vol. xviii, p. 653. 



2 Ibid., 1890, Vol. xviii, pp. i, 2. 



PROC. AMER. PHILOS. SCO. XXXVI. 15G. Z. PRIKTED DEC. 21, 189i 



