458 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



noose. In central Iowa there are beds equivalent to the Henrietta, but the sequence of strata 

 is different. 



"The lowest member of the measures is the Cherokee shale, which outcrops in a crescent- 

 shaped area following the outer lines of the outcrop of the Coal Measures from Kansas to north- 

 central Iowa. The shales vary in thickness from 200 to 600 feet along the outcrop of the next 

 higher formation and thin to nothing at their own outcrop. The formation is made up largely 

 of shale and sandstone and carries numerous important coal beds. The individual strata vary 

 ia character and thickness. from poiat to point, so that it is impossible to construct a general 

 section of more than local value. In the southwest, especially in southeastern Kansas and the 

 adjacent portions of Missouri, the beds are apparently more regular than elsewhere, and the 

 irregularities found farther north serve to mark this as an exceptional portion of the field." 



The persistent limestones of the "Upper Coal Measures," as well as the intervening shales, 

 have all been named in Kansas. In many reports these have been considered as separate 

 formations. In other reports they have been treated as members of somewhat more iaclusive 

 formations. Later work has shown that the earlier correlations of some of the limestones at 

 different points were erroneous. Agaia, some of the earlier names used have later been found 

 to be preoccupied by use for some other formation elsewhere. These facts have led to many 

 changes in the nomenclature of the Pennsylvanian of Kansas. 



In the table opposite is presented the stratigraphy of the Pennsylvanian of Kansas, as 

 contained ia several recent reports. Bulletin 211 of the United States Geological Survey gives 

 the synonymy of the several formations listed, with the fauna of each formation or member. 

 Bulletins 238 and 296 show the groupings and treatment of the rocks at still later dates, and 

 the latest is that quoted from volume 9 of the State report. 



ARKANSAS VALLEY AREA.. 



The area of Pennsylvanian strata of Kansas, Missouri, and Iowa is, in large measure, cut 

 off from the Arkansas Valley area on the south by the Ozark uplift. The two areas are con- 

 nected by a relatively narrow belt of outcropping rocks running southwestward through eastern 

 Oldahoma. In this narrow area, which has not been studied as much as the regions to the 

 north and south, there is a notable thickening of the formations toward the south; a running, 

 out of the limestones, so characteristic of the formations of Kansas, and the introduction of 

 sandy beds; and a downward transgression of the red clay, which to the north is character- 

 istic of the Permian beds but which in this region extends downward into the upper part of 

 the Pennsylvanian. As a result of these changes the stratigraphy of the Pennsylvanian in 

 central Arkansas and eastern Oklahoma is very different from that in Kansas. In part the 

 increased thickness is due to the appearance of older Pennsylvanian strata at the bottom of 

 the series. 



The second table opposite shows the stratigraphic nomenclature, with the thickness of some 

 of the strata, as given in the reports of the more important studies made in this field, in addition 

 to a correlation with the Pennsylvanian to the east, based entirely on the work of David White. 



For comparison, Purdue's section "^^^ in western Arkansas (Pike, Howard, and Sevier coun- 

 ties) and an abbreviated section from Kansas are also given. The Mississippian formations 

 underlying the Pennsylvanian in these sections are included in the table to show the character 

 of the contact at different points and as bearing on the stratigraphy of the Ouachita region. 



OUACHITA AREA. 



As already stated, the Ouachita area is cut off from the Arkansas Valley area by a great fault 

 or fault belt extending from Atoka northeastward and eastward. South of this fault the rocks 

 are closely folded or overturned as well as faulted. The result of this faulting and folding has been 

 to greatly shorten the north-south extent of the area covered by the Pennsylvanian. The writer ^= 

 has estimated that in the southern part of this area a section along Cossatat River, now 24 miles 

 long, was originally 35 miles long, and a section on Antoine Creek, now 20 miles long, was originally 

 also 35 miles long. As this estimate does not make any allowance for overthrust faulting, and 



