20 LIFE OF THE PLEISTOCENE 



white spruce and black spruce of today, are abundant in postglacial deposits 

 at Chicago, 111." 



1917. wright 34 seeks to explain the elevated beaches and the buried peat 

 deposits by the varying volume of water flowing through the different outlet 

 channels across Michigan. "The most difficult facts to account for are 

 numerous peat deposits underneath the Calumet or second beach. To explain 

 this accumulation of peat in that position, resort has been had to the supposi- 

 tion of a temporary land elevation. 



"But a simpler explanation follows from considering the variations in 

 amount of water passing through the Chicago outlet, occasioned by the open- 

 ing of the various channels giving access to Lake Michigan of the vast amount 

 of water stored up in the glacial lakes which occupied the Lake Erie basin. 

 Lake Maumee stood 200 feet above Lake Michigan and was lowered 50 feet 

 when the Ubly outlet was opened. Lake Whittlesey stood 150 feet above 

 Lake Michigan and extended over an area of several thousand square miles. 

 This was lowered 50 feet on the opening of the Saginaw outlet. Lake War- 

 ren stood 100 feet above Lake Michigan and covered an area much larger 

 than Lake Whittlesey, and it was lowered to approximately the present level 

 when the retreat of the ice opened the Mackinac channel." 



The opening of these outlets to the Grand River outlet probably added 

 somewhat to the volume of water flowing thru the Chicago outlet, but this 

 volume was not great enough to account entirely for the different stages of 

 Glacial Lake Chicago. The low water stage during which the peat deposits 

 were formed did not occur, probably, until after the Lake Whittlesey episode. 

 It is possible that the low water stage was coincident with the Lake Wayne 

 stage of the Ontario basin and that the subsequent elevation to the Lake 

 Warren level, and the shifting of the outlet to the Grand River Valley, caused 

 the rising of the Lake Chicago waters to the Calumet beach. 



1918. alden. 35 — In the discussion of the Quaternary geology of south- 

 eastern Wisconsin, this author devotes considerable space to the glacial stages 

 of Lake Chicago, the shorelines — Glenwood, Calumet, Toleston — being de- 

 scribed as in the papers of Leverett, Alden, Goldthwait, Salisbury, and At- 

 wood, previously mentioned. The statements relative to Lake Chicago and 

 those bearing on the postglacial and interglacial life considered in this volume 

 are discussed in several places in the following pages. 



III. Summary 

 A study of the literature relating to the postglacial history of the Chicago 

 Region shows that, while considerable information has been accumulated 

 concerning the biota of the old lake basin, little or no systematic field work has 



M Bull. Geol. Soc. Amer., XXVIII, p. 142, 1917. 



36 U. S. G. S., Prof. Paper 106, pp. 135, 136, 310-312, 326-339. 



