PROVINCIAL UNITY OF CONTINENTAL INTERIOR 

 COAL-FIELDS. 



CHARLES KE!YES. 



With their extreme simplicity of geological structure it seems 

 almost incredible that the coal-fields of the Continental Interior 

 should remain so long without even approximate correlation of 

 their several parts. That the Arkansas district, the Western 

 Interior area, the Eastern Interior field and the INIichigan basin 

 are essential parts of a single stratigraphic province there is 

 now little reason to doubt. Recent regional planation mani- 

 festly separates a once continuous plate by removing the coal 

 measures over the crests of broad gentle folds and preserving 

 from the effects of erosion the deposits lying in the troughs. 



The physiographic conditions existing when the coal measures 

 were laid down are not so very hard to restore in fancy. The 

 great plane of unconformity which characterizes the floor ovei 

 such a large part of the region is clearly a Mid Carbonic pene- 

 plain of remarkable extent and smoothness. It represents per- 

 haps the largest and most perfect peneplain known. It extends 

 from central Arkansas north and northeast far upon the crys- 

 talline Canadian shield beyond the Great Lakes. Without inter- 

 ruption and with gradual encroachment the marine coal-marshes 

 doubtless crept up towards the pole far into Canada. Late 

 Carbonic, Comanchan, Jurassic and Triassic warpings of the 

 earth 's crust were wide spread over the coal region. In southern 

 Minnesota the flexing devolved into a lofty mountain range that 

 rivaled the Appalachians of today. Other folds l>roader but 

 perhaps not so high developed elsewhere through the Continental 

 Interior. Between the base-leveling of Cretacic and Tertiary 

 times all topographic eminences were completely and smoothly 

 worn down. The once vast and continuous coal-field thus be- 

 came broken up into a number of separate basins possessing 

 much the character that they have at the present day. Inat- 

 tention to these fundamental stratigraphic facts is no doubt 

 the main cause of the failure to correlate the several State 

 sections. 



Half to three-quarters of a century ago, when the coal meas- 

 ures of the region first came in for systematic consideration, it 

 M^as widely thought that careful comparisons of the contained 

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