182 C. R. KEYES — A DEPOSITION AL MEASURE OP UNCONFORMITY 



only the lower 200 feet out of the entire 10,000 feet appear to belong to 

 the Lower Coal Measures as given by Drake. 



ARKANSAS SECTION 



The most complete section of the Coal Measures of Arkansas is that 

 constructed by Winslow for his unpublished report on the coals of the 

 state. The section has been, however, published by Stevenson.''^ Com- 

 paring his earlier section f v/ith this one, it is assumed that the lower or 

 eastern coal-bearing division corresponds to the Spadra stage, the inter- 

 mediate or barren division to the Sebastian stage, and the upper or west- 

 ern coal-bearing division essentially to the Poteau. 



As the positions of the higher coals in the Poteau were not well under- 

 stood in Arkansas, it seems probable that the Grad}' or Huntington coal 

 at the base of the Poteau and the lower coals occurring in the Spadra 

 stage were included in Branner's i)roductive beds. 



The Spadra formation is best developed in central Arkansas and is 

 believed to thin out westward, failing altogether before the limits of the 

 state are reached. Beneath this terrane Branner considers that there are 

 still about 18,000 feet of Coal Measures represented in the state. 



In this connection it must be again stated that the Poteau beds of the 

 Arkansas geologists do not form the Poteau group of Indian territor}^ as 

 designated by Drake, but correspond to the latter's Cavaniol group. 



Correlation of the Genkral Sections 

 stratigraphic relationships 



The detailed work done during the past decade in the various parts of 

 the Trans-Mississippian coal fields has enabled satisfactory correlations 

 to be made without falling back u})on the fossils. Various horizons have 

 been traced in the field, so that every portion of the area occui)ied by the 

 Coal Measures may now be considered as being very closely connected. 



If these correlations have been correctly carried out, it would appear 

 that, taking the section of the Missouri river as a standard, the serial 

 subdivisions are readily followed around the Ozarks occu})ying southern 

 Missouri and northern Arkansas. 



According to the accumulated stratigraphic evidence, there begins 

 south of the Kansas boundary a formation having no representative ter- 

 rane to the north. This formation rapidly gets thicker and thicker south- 

 ward and eastward until, if Branner's estimates are correct, it attains 



* Trans. New York Acad. Sci., vol. xiv, 1895, p. 51. 

 t Arkansas Geol. Survey, Ann. Kept., 1888, vol. iii. 



