IOWA ACADEMY OF SCIENCES. 57 



probably led to a misinterpretation of the real conditions that 

 prevailed during the period of their deposition. The purely 

 paleontological evidence, though somewhat meager, set forth 

 by Smith,* was intended by him to strengthen the view stated 

 above, that the Arkansas coal measures are the representatives 

 of the commonly recognized upper and lower divisions of the 

 Mississippi basin, taken together. However, a careful con- 

 sideration of the fossils noticed and a comparison with those of 

 other districts appear rather to indicate that, in Arkansas, only 

 the lower coal measures, or Des Moines series, is really pres- 

 ent. This is also in accordance with the results of various 

 other lines of investigation in the Ozark region. The correla- 

 tion of the Ai'kansas coal measures, with its great thickness, 

 and the Des Moines series of Missouri and Kansas, with a 

 thickness of only one-fourth of the first named, is fully 

 explained elsewhere. In a word, the shore -line during the 

 latter part of the Mississippian epoch was approximately along 

 the present axis of the Ozark uplift. North of that line ero- 

 sion of the land was taking place, now indicated by the great 

 unconformity of the base of the coal measures throughout the 

 greater part of the Mississippi basin. South of the line, shore 

 deposits were being laid down on a slowly sinking coast, within 

 that district, no secession of sedimentation. 



The Missourian series may, therefore, be regarded as not 

 being represented in any part of the Ozark dome, unless possi- 

 bly in some parts of Indian territory, where the Ouchita range 

 extends westward. 



The following is, then, a summary of the Carboniferous for 

 mations of the Ozarks and of their local equivalents: 



*Proc. American Philos. Soc , Vol. XXXV, pp. 313-285, 1896. 



