H. F. Bain — Limestone at Bethany, Missouri. 439 



looked for in the latter region. The persistence of these 

 minor subdivisions over the territory where they have already 

 been traced for more than one hundred and fifty miles, 

 suggests that the differences are due to widely acting causes 

 and brings into sharp contrast the unsettled and disturbed con- 

 ditions which apparently prevailed during the deposition of the 

 Des Moines beds. 



This manifest change in conditions affords a legitimate 

 basis for making the Bethany the dividing line between the 

 two divisions of the Coal Measures, even though it be recog- 

 nized that the faunal changes are in the proportion and abund- 

 ance of the species present rather than in the introduction of 

 new forms. The old fauna adapted itself to the new condi- 

 tions and there was a change merely in the balance between 

 the species. 



The taxonomic rank of the Bethany and its subdivisions is 

 indicated in the following table : 



System 



Series 



Stage 



Sub stage 



. 



Missourian 



Undifferentiated 





Carboniferous 



Bethany 



Westerville ? 

 De Kalb 





Des Moines 



Winterset 



Earlham 



Fragraental 



It is probable that the Westerville limestone will be found 

 to be better included with the next higher division when that 

 shall be studied, but for the present it may be conveniently 

 considered in connection with the Bethany. 



Des Moines, Iowa, April 18, 1898. 



