THE LIFE OF GLACIAL LAKE CHICAGO 69 



A. THE GLENWOOD STAGE 3 (PLATE XXXLT.) 



The initial stage of Lake Chicago is known as the Glenwood. As the ice 

 melted back of the Valparaiso moraine, a crescent-shaped body of water came 

 into existence, which stood at a height of 60 feet above the present level of the 

 lake for a period, but soon fell to 55 feet, after cutting thru the lowest notch 

 in the Chicago outlet below Lemont. At this stage the southern portion of 

 the lake extended from Winnetka west and south to Norwood Park, Oak 

 Park, LaGrange and Palos Park, southeast to Glenwood, Illinois and Dyer, 

 Indiana, continuing easterly and northeasterly thru northern Indiana and 

 southwestern Michigan. Mt. Forest and Blue Island were conspicuous islands, 

 and the Desplaines River and the Sag formed two wide outlets, thru which 

 the gathering waters probably rushed with great velocity, finding an outlet in 

 the Illinois and Mississippi rivers. Three bays of considerable size were 

 formed: Skokie Bay and Chicago Bay (the latter being apparently almost as 

 large as Skokie Bay) on the north and Desplaines Bay on the west. Well- 

 marked sand spits developed across the mouth of Skokie Bay and of Desplaines 

 Bay, known respectively as the Skokie spit and the Oak Park spit. Small bays 

 existed on the southern shore of the lake, as at Dyer, Indiana. The large 

 bays were doubtless swampy at their heads and along their shores. 



Life 



There is no evidence of aquatic life during the Glenwood stage; this is as 

 would be expected in the icy waters melting from the glacier. The mastodon 

 and mammoth probably wandered along the beach. The remains of these 

 animals have been found in Haas' gravel pit in Oak Park, 4 and near Evanston, 

 Glencoe, Naperville, and Wheaton. 5 The oyster shells and other mollusks men- 

 tioned by Leverett 6 were probably introduced by early natives in graves. The 

 writer has examined this and other gravel pits on the Glenwood beach and no 

 evidences of life have been found. 



B. THE BOWMANVILLE LOW WATER STAGE 7 



The Glenwood high water stage was followed by a period of low water when 

 the level of the lake fell to about 10 feet above the present level. Conclusive 



z The maps of Lake Chicago have been compiled from the works of Leverett, Alden, and 

 Goldthwait, with a few additions by the author. 



4 Leverett, Pleistocene Features, p. 71. 



5 Anderson, A Preliminary List of Fossil Mastodon and Mammoth Remains in Illinois 

 and Iowa, pp. 9-10. 



8 Pleistocene Features, p. 70. 



7 As this stage seems equal in value to the Glenwood, the Calumet, or the Toleston stage 

 it is given a distinct name. As its development is most pronounced near the old village of 

 Bowman ville, this name is suggested for the stage. 



