452 THE ILLINOIS GLACIAL LOBE. 



Reference has been made to the beachlets which occupy the interval 

 between the main beach and. the present shore of the lake. These do not 

 form continuous lines around the head of the lake, but those in the vicinity 

 of the Chicago University and Jackson Park die out in a marsh which sets 

 in a short distance south of the park, and those in Lake County, Indiana, 

 die out at their western ends in a sandy plain which borders Wolf Lake, 

 Lake Calumet, and other small lakes near the State line. This sandy plain 

 stands but 5 to 8 feet above the lake, and was apparently an open bay at 

 the time these bar-like features were forming. But it has now become filled 

 with sand, leaving Lake Calumet and the other small lakes as its dwarfed 

 representatives. The beachlets stand only 10 to 12 feet above lake level 

 (except where coated by wind-drifted sand), and, as noted above, seem 

 referable to the action of the present lake rather than to Lake Chicago. 



The outlets of the lake at the time the Third beach was forming appear 

 to have been along three lines — the first, that occupied by the mouth of the 

 Chicago River and the south branch of the Chicago River (reversed); a 

 second along the marsh referred to above as leading from the south part of 

 Hyde Park Township northwestward between Englewood and South Lynne, 

 which connects with the south fork of the Chicago River north of the Union 

 Stock Yards; a third leading westward from Riverdale along the Sag out- 

 let. The broadest of these outlets is that leading past Englewood and the 

 Union Stock Yards, and it is possible that the other outlets became nearly 

 closed b}^ sand before this outlet was abandoned. 



The altitude of this beach in Illinois and Indiana is nowhere more than 

 20 to 22 feet above the lake, except where wind has drifted sand to higher 

 levels. The outlet could not well have been cut below a level 8 feet above 

 the lake, that being the altitude of the Chicago Outlet for several miles 

 below its junction with the present Des Plaines River. The depth of the 

 water in the outlets would, therefore, be 10 to 12 feet or less. As beaches 

 are often built up to a height of 4 or 5 feet above the ordinary level of the 

 lake, it seems probable that the ordinary stage of water was not more than 

 15 feet above the present stage of Lake Michigan, thus leaving but 7 feet 

 depth of water in the outlet. The Sag outlet reaches nearly 15 feet above 

 the level of Lake Michigan; hence it was probably only a minor line of 

 discharge. 



As hinted above, the reference of this beach to the same lake which 

 formed the higher beaches is not made with any degree of confidence. 



