74 ILLINOIS ACADEMY OF SCIENCE 



FURTHER NOTES ON THE POST-GLACIAL BIOTA 

 OF GLACIAL LAKE, CHICAGO 



BY FRANK C. BAKER 



ZOOLOGICAL INVESTIGATOR NEW YORK STATE COLLEGE OF 

 FORESTRY, SYRACUSE UNIVERSITY 



At the Chicago meeting of the Illinois Academy of Science 

 in 19 11*, the writer presented certain facts concerning the biota 

 contained in the sedimentary strata of the bed of Glacial Lake 

 Chicago. Since that time data have been accumulating which 

 have added largely to our knowledge of the life of these early 

 days. Attention has also been directed to the southwestern 

 portion of Michigan, bordering Lake Michigan, which contains 

 sedimentary deposits referable to several of the lake stages. 



To understand the northward migration of the life, one must 

 have clearly in mind the condition of this part of the country 

 as the great ice sheet melted back into the Michigan basin. 

 There was at first a large glacial lake in the Kankakee marsh 

 area, known as Lake Kankakee, which extended northeasterly 

 almost to South Bend; later came Lake Dowagiac which ex- 

 tended northeasterly up the area now occupied by the great 

 Dowagiac swamp; still later, after this drainage was largely 

 abandoned, a long arm of glacial Lake Chicago extended into 

 Michigan and connected with the Grand River outlet of glacial 

 Lake Saginaw. 



Just how rapidly the biota followed the retreating ice is not 

 known, but we may safely infer that certain hardy types (as 

 for example the Physas, some Lymnseas, Sphaeria, Planorbis, 

 etc), took advantage of the new water courses at a very early 

 time. It is this cold temperate, almost subarctic fauna that is 

 found in the earliest deposits of glacial Lake Chicago. 



Many, if not all, of the lakes in southwestern Michigan, 

 (including Berrien, Cass and Van Buren counties), contain 

 marl beds of post-glacial origin. The life entombed in these 

 marl deposits, consisting of mollusks, reached these lakes, for 

 the most part by direct migration from the region south of the 

 Wisconsin ice sheet. In what manner and by what routes they 

 came is one of the most interesting questions open to the 

 student of zoogeography. Three localities in the region under 

 discussion contain the remains of a more ancient life, one pre- 

 viously known, the others here recorded for the first time. 



1. Trans. 111. Acad. Sci., IV. pp. 108-116, 1912. 



