THE LIFE OF GLACIAL LAKE CHICAGO 91 



and St. Clair outlets. At first nearly all of the discharge was by way of Chicago, 

 but as that outlet was controlled by a rock sill, the greater outflow was shifted 

 to the St. Clair outlet, that being in till which was cut thru in a relatively short 

 time. Of the Chicago outlet at this time Taylor 59 says: "The time of this 

 large-volume discharge at Chicago was the time when the Toleston beach was 

 made, and if there was a beach of Lake Chicago there before and controlled 

 by the same sill, it must have been overwhelmed and worked over entirely by 

 Lake Algonquin waters." This is probably just what did happen, the first or 

 Toleston beach being formed when the water dropped from the 35 (Calumet) 

 to the 20 (Toleston) level; the beach usually called Toleston is evidently what 

 is here designated as Hammond and was formed during the large-volume dis- 

 charge following the low water or Kirkfield stage. Lake Chicago at this time 

 had about the same outline as during the Toleston stage. Mollusks and other 

 animals survived the low water period, and an extensive biota is preserved in the 

 strata of this second high water stage. 



a. Wilmette Bay {North Shore Channel) 



Marl and silt beds in this channel south of Devon Avenue contain a varied 

 biota referable to the Hammond stage. 



Plants 



Potamogeton species Najas species 



Scirpus species Nympkaea advena 



Carex species Typha latifolia 



Animals 



Sphaerium levissimum Campeloma integrum 



stamineum VdLvata tricarinata 



rhomboideum Amnicola limosa 

 " flamim " lustrica 



sulcatum Physa warreniana 

 " solididum " Integra 



striatinum Planorbis antrosus 

 Pisidium compressum " campanidatus 



" affine " trivolvis 



" noveboracense " deflectus 



" splendidulum " parvus 



" variabile Galba reflexa 



virginicum Lymnaea stagnalis appressa 



Wilmette Bay had about the same outline at this time as during the Toles- 

 ton stage (see Plate XXXVIII). North of Devon Avenue the bay was shallow 

 with swampy shores. The water contained such plants as Chara and 

 Potamogeton, and the shores were probably lined with Typha. This shallow, 

 marshy portion was over four miles long and from one to two miles wide. This 



89 Smith. Rep., 1912, p. 319. 



