THE COAL MEASURES OF ARKANSAS 357 



strata once extended unbrokenly over the whole area now 

 occupied by the uplift, and that they were removed through 

 erosion. 



As already remarked the great thickeningof the Coal Measures 

 begins to make itself apparent immediately south of the Boston 

 mountains ; north of this range the stratigraphy has been more or 

 less clearly understood. The two main subdivisions are clearly 

 defined over all of the northern region. There they represent 

 a lower, or coastal facies and an upper, or marine phase. The 

 plane separating them is the base of the first thick limestone 

 above the Mississippian series. This formation is now called the 

 Bethany limestone. It is a marked and persistent feature of 

 surface relief from north-central Iowa, where it emerges from 

 beneath the Cretaceous, southward through northwestern Mis- 

 souri, and southeastern Kansas, to the Indian Territory line, 

 beyond which it has not been traced in detail, although at that 

 point it still continues to be an important and easily recogniz- 

 able ridge. 1 



Regarding the southern part of the coal field much has been 

 written, but it has only been very lately that definite data have 

 been given, that enables comparisons with the northern districts 

 to be made. The facts recently published have a special impor- 

 tance at this time for the reason that they strongly support cer- 

 tain views concerning the physical conditions, the existence of 

 which have been, for some time, suspected, and enable several 

 statements to be formulated regarding the character of Carbon- 

 iferous deposition in the region. The data particularly referred 

 to are contained in a paper by J. P. Smith 2 on the "Marine 

 Fossils from the Coal Measures of Arkansas." While the facts 

 therein presented are not nearly as complete as is to be desired, 

 they nevertheless appear sufficient, when taken in connection 

 with information derived from other sources, to permit several 

 pregnant deductions to be made. 



One of the most noticeable features of the Carboniferous 



1 Am. Jour. Sci., (4), Vol. II, pp. 222-225, 1896. 



2 Proc. American Philos. Soc, Vol. XXXV, pp. 213-285, 1896. 



