MISSISSIPPIAN SEAS IN ILLINOIS 581 



The place of origin of the bowlders. — As Montclare is 165 miles 

 in a northeasterly direction from the nearest known Mississippian 

 outcrop in the Mississippi Valley, the question at once arises: 

 From where were these Mississippian bowlders transported by the 

 glaciers'? The general direction of ice movement in the Chicago 

 region during the last glacial epoch was somewhat west of south, 

 the published records of the directions of glacial striae west of the 

 city showing directions varying from S.57 W. to due west. 1 



Considering the known direction of glacial ice movement, the 

 first inference is that the bowlders may have been transported from 

 the known Mississippian outcrops in Michigan, but a careful 

 consideration of the Mississippian formations of that state and of 

 their faunas makes such an origin highly improbable. 



The Mississippian section of Michigan as given by Lane 2 has 

 been followed by all later writers. 



In this section the following subdivisions are recognized: 



Bayport or Maxville limestone: Light and bluish cherty 

 limestones and calcareous sandstones. 



Michigan series: Dark or bluish limestones and dolomites, with 

 gypsum and blue or black shales; some reddish or greenish shales 

 and dark or red sandstones. 



Marshall sandstone: White and red sandstone, often pyritic, 

 peanut conglomerates, sandy shales, whetstones, and red shales. 



Coldwater series: Blue shales with nodules of iron carbonate, 

 sandstone, subordinate streaks of fine-grained limestone, black 

 shale at the base. 



Berea sandstone: White sandstone, nowhere exposed in the 

 state. 



The published list of fossils from these Michigan formations 3 

 shows them to be faunally related to the Mississippian of Ohio 

 rather than to the Mississippi Valley formations. Writers are not 

 altogether in accordance regarding the correlation of these for- 

 mations, but, giving the widest possible latitude, the Montclare 

 bowlders must have been derived from a formation whose age was 



1 Chicago Geological Folio, pp. 506. 



2 Annual Report, Geological Survey of Michigan, 1908, pp. 74-86. (1909.) 



3 Geological Survey of Michigan, Vol. VII, Part II, pp. 253-70. 



