l«^-»7.] DRAKE — THE GEOLOGY OF INDIAN TERRITORY. 361 



Carboniferous into Permian beds. A rough estimate giVes a total 

 thickness of 25, GOO feet for the Coal Measures deposits. Most of these 

 strata were laid down near shore and are, therefore, subject to the 

 irregularities of near-shore deposits. Arenaceous clay shales, sand- 

 stones, limestones, coal, grits and conglomerates occur in relative 

 abundance in the order named. Well-marked beds that may be 

 used for making stratigraphic divisions are for the most part want- 

 ing. The limestone beds are mainly confined to the northern part 

 of the field and to the central part of the Upper Coal Measures. The 

 shale and the sandstone beds are so local and repeated in such litho- 

 logical uniformity that they serve poorly for divisions ; fossils, espe- 

 cially in the southern part of the field, are of rare occurrence. The 

 larger coal beds, with some irregularities, extend across the entire 

 field and furnish the best means of grouping the formations. The 

 workable beds of coal are all confined to the lower part of the 

 Upper Coal Measures. The Coal. Measures deposits will be con- 

 sidered under the following classification : 



{ Upper Coal Measures. 



( Poteau group. ^ 

 (Cavaniol group. ^ 



Coal Measures. ^^ 



(^ Lower Coal Measures. 



Plates II and VII show the relation of these groups. 



The Lower Coal Measures produce no coal ; the Cavaniol group 

 contains the workable beds, and the Poteau group contains some 

 thin ones. 



Lower Coal Measures. 



There are three different areas of the Lower Coal Measures in 

 this field. One lies in the southeastern part of the region, and is 

 bounded on the north by a line running along the southern base of 

 the Poteau mountains and the north side of Fourche Melane valley 

 and Jack Fork mountains; from the latter place the bounding line 

 runs southwesterly and passes out of the field. This area includes 

 the Fourche Melane valley and the upper part of the Kiamichi 

 valley and Walker, Black Fork, Kich, Blue, Windingstair, Jack 

 Fork and Kiamichi mountains and the intervening areas. 



1 These names were taken from the names of mountains in the southeastern 

 part of the field where the beds included in those groups are well represented. 



