582 W. W. DAVIS 



included within the time of deposition of the Coldwater, Marshall, 

 and Michigan formations of Michigan. The published faunal lists 

 from all these formations are made up largely of pelecypods, and 

 from all the available lists a single species, S pirifer forbesi (and this 

 identification is admitted to be very questionable) , is recorded from 

 the Michigan series, which has been identified in the Montclare 

 collection. Even if the identification of this species from Michigan 

 is correct, it is still quite evident that the Montclare bowlder fauna 

 has no relationships with the Michigan Mississippian which are 

 worthy of consideration. Furthermore, the lithologic character 

 of the Montclare bowlders is totally different from that of any of the 

 Michigan formations. 



From the foregoing consideration of the faunal and lithologic 

 characteristics of the Mississippian formations of Michigan it may 

 be assumed as a demonstrated fact that the Montclare bowlders 

 were not transported from across Lake Michigan to their present 

 resting-place. 



The only alternative conclusion in regard to the source of these 

 bowlders is that they were originally in place at no great distance 

 from where they now lie. Such a conclusion is further confirmed 

 by the physical condition of the bowlders themselves. They are 

 angular in outline and exhibit much less wear than most of the 

 associated bowlders. The present weathered condition of the 

 bowlders is probably original weathering accomplished before they 

 were moved by the glacier. This is suggested by the different 

 degrees of weathering of the bowlders themselves and by the dif- 

 ferent surfaces of the same bowlders. Furthermore, the other 

 bowlders of similar composition which were buried with the 

 Mississippian bowlders in the glacial debris are still essentially 

 unweathered, even upon their surfaces. 



Conclusions. — A study of these Montclare glacial bowlders of 

 Mississippian age seems to establish the following important 

 conclusions : 



i. There existed, previous to the last glacial advance, an outlier 

 of Mississippian rocks in northeastern Illinois, probably resting on 

 limestone of Silurian age. The remnants of such an outlier may 

 well be in existence, completely buried at the present time by 



