BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 12, PP. 173-196, PL. 19 APRIL 18, 1901 



A DEPOSITIONAL MEASURE OF UNCONFORMITY 



BY CHARLES R. KEYES 



(Read before the Society December 28, 1900) 

 CONTENTS 



Page 



Introductory 1 74 



Carboniferous and its subdivisions in the Mississippi valley 174 



Principal coal-bearing formations 170 



Extent and character 17H 



Productive coal series in the north 176 



Productive coal series in the south 177 



Geological sections of the region 177 



General considerations 177 



Iowa section 1 78 



Missouri section 179 



Kansas section ... 179 



Indian Territory section 179 



Arkansas section 182 



Correlation of the general sections ... 182 



Stratigraphic relationships 182 



Faunal comparisons 183 



Floral parallelism 185 



Relations to Texas section 186 



Correlation of Western Interior and Alleghany sections 187 



Unconformity at base of Coal Measures . 187 



Extent and nature 187 



Topography of the old land surface 1 88 



Significance of the unconformity 1 88 



Basal series of Coal Measures in Arkansas 189 



Thickness and general character 189 



Relations to the underlying Mississippian 190 



Superior delimitation of basal series 191 



Homogeneity of the Arkansas series 191 



Subdivisions 191 



Relations of the Arkansan series to great unconformity 192 



Correlation 192 



Depositional measure of erosion period 192 



Role of the Ozark uplift 193 



Thickness of the Carboniferous 194 



Conditions under which Arkansan series was deposited 194 



Recapitulation 195 



XXVI— Bull. Geol. Soc. Am.. Vol. 12, 1900 (173) 



