78 LIFE OF THE PLEISTOCENE 



To the north the lake developed a large, distinct embayment (Plate 

 XXXVI). From the shore 'line north of Wilmette (now cut away to the 

 extent of a mile or more) a hook was formed by the southward drift. At about 

 the same time an off-shore barrier of sand was formed which extended in a 

 north and south line from Bowmanville to Evanston. It seems evident that 

 this bar (the Rose Hill bar) was largely built under water during the Calumet 

 stage, as only the crest is above the 35 foot contour. The pronounced bar 

 and peninsula extending from Evanston southward was built up during the 

 interval between the Calumet and Toleston stages on this off-shore barrier. 

 During the Calumet stage there were evidently several breaks in the bar, which 

 formed shallow water connections between the bay and the larger lake. 



The west side of the barrier developed several pronounced hooks which 

 indicate that wave and current action were strong. Besides several minor 

 hooks and ridges, one large hook extended from Rogers Park into the lake in 

 a northwesterly direction, for the distance of a mile. The dominant wind was 

 evidently from the south or southwest, which caused the formation of this 

 strong hook, as well as the bow-shaped curve of the termination of the barrier 

 west of Bowmanville. As the town of Wilmette lies on the floor of this ancient 

 embayment, it has been named Wilmette Bay. 29 



a. Life 



It is probably true that the rising of the waters initiating the Calumet stage 

 exterminated much of the biota occupying the lake during the Bowmanville 

 stage, covering it with a layer of sand and gravel. That there was no life in 

 the waters during the Calumet stage does not follow, however, and it is highly 

 probable that the varied naiad fauna which took possession of Wilmette Bay 

 invaded Lake Chicago sometime during the lowering of the lake from the Calu- 

 met (35 foot) to the Toleston (20 foot) level. In the bed of the Calumet- 

 Sag channel the Unios Me directly upon the boulder pavement which forms the 

 covering of the till, and these are covered by gravels which were laid down dur- 

 ing the Toleston stage, mostly in the later part of this stage. These are con- 

 sidered in the discussion of the Toleston stage. 



Leverett 30 and Goldthwait 31 have both stated that no evidences of life 

 have been found in the Calumet beach. Those who have studied the recent 

 beaches of the Great Lakes know that life is frequently absent from long 

 stretches of beach, and when present at one time may be at another totally 

 obliterated by the pounding of the waves and the moving of the sand. As a 

 rule, fresh water beaches are poor preservers of the remains of life while quiet 

 lagoons and bays are the best preservers, even the delicate wings of insects 



29 Goldthwait, Records of Extinct Lakes, p. 62. 

 80 Pleistocene Features, p. 73. 

 31 Records of Extinct Lakes, p. 63. 



