114 ILLINOIS ACADEMY OF SCIENCE. 



far south as Texas and as far north as southern Wisconsin and 

 southern Michigan, it is perhaps unwarranted to infer that because 

 of the presence of Unio crassidens there was a warmer chmate at 

 this time, yet this seems not at all improbable in view of the 

 Green Bay record. 



It is interesting to note that the interglacial beds of the Don 

 Valley near Toronto, Canada, contain several of the species which 

 occur in the Chicago deposits. As these are mostly Mississippi 

 Valley species they must have reached this point by way of the 

 southwest and they possibly migrated through an ancient water- 

 way near the present site of Chicago. For comparison, the Unios 

 of the two regions are placed in parallel columns. ^^ 



Don. Chicago. 



undidatus. undulatus. 



rectus. 



luteolus. luteolus. 



gibbosus. gibbostis. 



phaseolus. 



trigonns. trigonus. 



coccineus. coccineus. 



occidens. 



solidus. 



davits. 



pyramidatus. 



crassidens. 



reAcxa. 



elegans. 



ventricosus. 



pustulosus. 



lachrymosus. 



It will be noted that but five species are common to both 

 deposits, while six species are found in the Don beds which are 

 absent from the Chicago beds, and six species found in the Chi- 

 cago beds are absent from the Don beds. The Don deposits are 

 believed to have been laid down in a comparatively warm climate, 

 as indicated by both the plants and animals. 



It is important that post-glacial deposits on both the east and 

 the west shores of Lake Michigan should be carefully studied 

 and their biologic contents accurately noted, to the end that these 

 facts may be correlated with those herein presented. Sedimentary 

 deposits are known to exist at Green Bay and at Milwaukee, and 

 these should contain ample evidence of post-glacial life. Studies 

 now in progress in other parts of the Chicago Lake basin are 

 expected to add much evidence confirmatory of the interpretation 

 herein presented. 



"See Coleman, Interglacial Periods in Canada, p. 16, 1906. 



