A DISCUSSION AND CORRELATION OF CERTAIN 

 SUBDIVISIONS OF THE COLORADO FORMATION 



A fairly accurate correlation of the subdivisions of the 

 Colorado formation in the central-interior province is not 

 difficult. Although the work done in the different areas of 

 the province has been largely independent, yet divisional 

 lines are not strikingly inharmonious. Points of separa- 

 tion are more easily determined in certain areas than in 

 others. In specific parts of the province confusion in regard to 

 divisional lines seems to have arisen, due to misinterpretations 

 of a palaeontological nature, while in other parts the confusion 

 seems to be due to lithological similarities. The points involved 

 are, on the whole, minor ones, and, perhaps, are not worthy of 

 any very elaborate discussion. Nevertheless, stratigraphical 

 geology is, at its best, complex, and therefore should receive 

 every additional contribution which will tend to relieve its com- 

 lexity. 



The Colorado formation has not been studied as thoroughly 

 and systematically as is desired, yet a study has been made of a 

 sufficiently large number of areas to warrant the establishment of 

 more general division lines. The areas of the central-interior 

 province which have been studied somewhat in detail are : 

 The southeastern Colorado area, the Black Hills area, the east- 

 ern Dakota area, the Iowa-Nebraska area, and the Kansas area. 

 Since I am more familiar with the detailed stratigraphy and 

 palaeontology of the last-named area I will discuss it and use it 

 as a standard by which to correlate the other areas. 



In the Kansan area two principal groups have been recog- 

 nized for the Benton series. These groups are, the lower or 

 Limestone group and the upper or Shale group. The division 

 is based primarily on lithological grounds as the names indicate. 

 The Limestone group admits of five subdivisions, such divisions 



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