THE COAL ME A S URES OF A RKA NSA S 359 



Winslow, 1 Stevenson, 2 Branner 3 and others. While the total 

 thickness of the Coal Measures is doubtless somewhat over- 

 estimated by these authors, it is manifest that the formation is 

 very thick — several times as great as it is farther northward. 



The subdivisions of the Arkansas Coal Measures that have 

 been recognized have not always been the same. In several 

 instances they have been quite different. The classifications have 

 been either noncommittal as to exact correlation with other 

 regions, or they have been very general. The members dis- 

 tinguished have been largely for convenience in local field work. 

 The tendency has been, however, to regard the Coal Measures of 

 this region as about equivalent to the Coal Measures (" upper and 

 lower divisions") of other districts north and east, with the 

 intimation, in the later notes, that the so-called Permian of the 

 western part of the Mississippi basin, may be present to some 

 extent, as for example on Poteau mountain. In the latest con- 

 tribution to the subject by Smith, 4 the "Upper Coal Measures" 

 and the " Lower Coal Measures " of the Arkansas valley are paral- 

 leled with the similarly named formations of the Missouri region. 

 The Poteau mountain beds are included. The conclusion is that 

 "there is not sufficient reason for classing the Poteau moun- 

 tain beds with the Permian, but their fauna, as well as strati- 

 graphic position, place them very high in the Coal Measures, 

 since they are like the fauna and position of the Mississippi valley 

 Upper Coal Measures. These beds derive an additional interest 

 from the fact that on Poteau mountain iooo feet of shale, in 

 which no fossils were sought for, lie above the thin layer from 

 which the entire collection was taken ; thus the chance of find- 

 ing true Permian beds in that region are very good." From 

 this it will be seen at once that the Arkansas section is regarded 

 as representing the Des Moines and Missourian series of Missouri 

 and Kansas, as embraced between the Mississippian limestones 



'Bull. Geol. Soc. America, Vol. II, pp. 225-242, 1891. 



2 Trans. New York Acad. Sci., Vol. XV, pp. 50-61, 1895. 



3 Am. Jour. Sci., (4), Vol. II, p. 235, 1896. 



4 Loc. cit. 



