300 C. K. KEYES — THK PRINCIPAL MISSISSIPPIAN SECTION*. 



In regard to the minor subdivisions of the four groups above men- 

 tioned much might In- said. The several sectional names proposed at 

 various times have had wide value- and, moreover, have been applied 

 rather loosely. 



In the Kaskaskia the upper shales and the lower limestones of Chester. 

 Illinois, have been differentiated, while the Aux Vases sandstone has 

 been placed at the base of the group, provisionally. It has not had. as 

 vet, sufficient study over its entire exposure to satisfactorily consider its 

 relationships in all its phases. Certain it is, however, that when the con- 

 tinental area north of the present city of St. Louis was being subjected to 

 denudation prior to the deposition of the lower Coal Measures the great 

 ^sandstone was laid down south of that point in the shallow littoral waters 

 of the interior sea. 



The St. Louis group has been divided into three limestone. Of these 

 the Ste. Genevive has never come into general usage, and practically has 

 been forgotten. The St. Louis limestone itself has been widely recog- 

 nized, and in many places the lower portions have been correlated with 

 the Warsaw beds as developed at the mouth of the Dea Moines river. 



The Osage group is now made to include all five of the hitherto recog- 

 nized beds, the Warsaw proper, the geode layer, the Keokuk, and the 

 upper and lower Burlington limestones. 



The Kinderhook group is a three-fold division whose several members 

 are strongly contrasted and persistent over wide areas. 



The history of the shore-line shifting of the great interior sea is a theme 

 for detailed elucidation. Much has already been done toward this end. 

 I>ut some further information is requisite before a satisfactory presenta- 

 tion of the subject can be made. 



