LAKE CHICAGO AND ITS OLD SHORE LINES 87 



the downstream end of the obstruction, forming a rapids with 

 violent current that worked furiously at cutting out the rock. 

 Gradually the rapids ate their way through these strata until 

 finally they reached the upper end of the rock dam. The rock 

 barrier once removed, the stream rapidly cut through the gravel 

 of the old valley train to the lake and another drop in the lake 

 level occurred, of some fifteen feet. A reference to the map 

 (Fig. 51) will show that through the Chicago outlet was flowing, 

 during the Calumet stage, not only the waters from the front of 

 the Michigan lobe, but also that from much of the Saginaw and 

 Erie lobes. This great stream was undoubtedly a vigorous 

 worker. 



So Lake Chicago assumed a new level, the Tolleston stage 

 (Fig. 52), some twenty feet above present lake level or about six 

 hundred above sea-level. It held it long enough to cut a new 

 shore line and deposit extensive beaches. The location of these 

 Tolleston beaches is shown on the map (Fig. 53). 



The main Tolleston beach abuts on the lake shore not far 

 north of the campus of Northwestern University which it crosses 

 from North Gate, running inland beneath Herck and University 

 Halls. It runs through the city on the east side of Chicago 

 Avenue and in South Evanston is followed pretty closely by 

 Clark Street. Thence it continues south of Calvary Cemetery, 

 through Rogers Park and Rose Hill, bordering the old Rose Hill 

 Bar. From Garfield Park to Hawthorne it is very plain. It is 

 easily traced east from Summit, thence southeast through 

 Auburn Park and Burnside. Stony Island, an island new born 

 at this Tolleston stage of the lake, appears here close offshore, 

 and the Tolleston beach is very plain on its northern side. From 

 Burnside the beach runs south through Kensington, then swings 

 east and follows quite closely the general present contour of Lake 

 Michigan. 



It will be noted that both north and south outlets on either 

 side of Mount Forest Island are pretty well closed by the end 

 of this stage, for a great sand spit had been built all across the 



