MISSISSIPPIAN SEAS IN ILLINOIS 583 



glacial drift. The actual position of this outlier cannot now be 

 determined, but it was at no great distance from the present position 

 of the bowlders and may well have been within the present limits 

 of Chicago. 



2. The limestone comprising this Mississippian outlier con- 

 tained a prolific fauna of brachiopods, crinoids, and other forms of 

 life, every species of which, so far as they have been certainly 

 identified, is present also in the rocks of lower Osage age in the 

 Mississippi Valley. The whole association of species suggests a 

 very definite correlation of these Mississippian rocks with the Lower 

 Burlington limestone of western Illinois, Iowa, and Missouri. 

 There is no suggestion whatever of any faunal connection with the 

 Mississippian formations of Michigan. 



3. On the basis of the two foregoing conclusions, the extension 

 into northeastern Illinois of the Mississippian sea, which occupied 

 the Mississippi Valley region in early Osage time, may be assumed. 



