450 BOTANICAL GAZETTE ' [june 



confined 



The 



writer is under great obligation for the verification of all species 



many- 



New 



Mr. George B. Kaiser, 



curator of the Sullivant Moss Society, and Dr. LeRoy Andrews, 



many 



assistance to Dr. Henry C. ( 

 of the University of Chicago. 



Description of region 



The city of Chicago occupies a part of the land once covered 

 by Lake Chicago (9). This was a post-glacial body of water 

 formed in the depression between the Valparaiso moraine and the 

 edge of the retreating ice sheet as it slowly moved northward. 

 That the water remained comparatively stationary at certain 

 levels for a considerable length of time after the recession first 

 began, is proved by the presence of at least three distinctly defined 

 old lake beaches. The Glen wood beach marks the edge of the 

 Valparaiso moraine, and is the beach first formed by the impounded 

 water; the Calumet beach was formed at a later period when the 

 water was about 20 ft. lower than at the Glenwood stage; the 

 third or Tolleston beach records a period when the water had 

 receded until it was 20 ft. below that of the Calumet. The beach 

 of the present lake is not far from 20 ft. lower than the level of 

 the Tolleston stage of Lake Chicago, making the surface approxi- 

 mately 60 ft. below that of the original body of water. Going 

 northward along the west shore of Lake Michigan one crosses, in 

 the vicinity of Rogers Park, several old beach ridges of the Tolleston 

 stage. Here the present lake is eroding material deposited by the 

 older body of water. Farther north, about Winnetka and Glencoe, 

 these old beaches have disappeared, and the lake is encroaching 

 upon a bluff of morainic clay, where may be found all stages of 

 clay ravines, from freshly eroded gullies to old ravines in an 

 advanced stage of mesophytism. These ravines have their origin 

 in the small streams which have cut back into the surrounding 

 oak upland. Facing the lake the bluffs are in some places entirely 

 bare of vegetation, while in others they have become well covered 



