THE LIFE OF GLACIAL LAKE CHICAGO 



103 



Physa gyrina 



" integra 



Ancylus fuscus 



" parallelus 



Segmentina armigera 



Planorbis trivolvis 



" campanulatus 



" antrosus 



" deflectus 



exacuous 



" parvus 



Galba reflexa 



" palustris 



obrussa 



" caperata 



Lymnaea stagnates appressa.. 



eS p cu 



menu 



H £ 



OH 



" ft 



cS Hi 



ft& 



s u S 



d u - 



2 « O O 



KflH J 



3 S 



c S 

 ►JH 



w £- tw 



° ? -a 



o k. 2 

 & & S 

 .2*2 ft 



fi rj 1) 



p* 



a a 



hJH 



Total species of Mollusca 

 Crustacea 



Cambarus blandingi acutus 



Vertebrates 



Mergus serrator 



Amia calva 



Lepomis species 



Silurid or Cyprinoid 



36 



35 



58 



26 



17 



13 



The portion of Wilmette Bay from which the above data was obtained lies 

 north of Foster Avenue and south of Devon Avenue. It is therefore a typical 

 portion of the bay, the sedimentary strata of which faithfully portray the 

 history of this body of water. The changes in the biota are marked and sup- 

 port the statement of Chamberlin that there should be a succession of strata 

 after each glacial period ranging from cold to warm and from warm to cold. 

 In this case the change is only from colder to warmer, as would be the case when 

 but the first part of a postglacial period is included. Should the ice again 

 form and again advance, ponding the waters of the lake, there would be a 

 reversal of the fife, ending with arctic or subarctic types, which would be 

 covered finally by the succeeding till sheet. At Toronto the oncoming of the 

 glacial ice is reflected in the biota and we may see the opposite of the Chicago 



