GEOLOGICAL AND NATURAL HISTORY SURVEY. 55 



THE CHICAGO OUTLET AND BEACHES OF LAKE 



CHICAGO. 



PREVIOUS WRITERS. 



It is perhaps impossible to determine who was the first person 

 to recognize the evidence or form the conception of a southwest- 

 ward outlet from Lake Michigan to the Des Plaines. Inquiry 

 among the old residents of this region shows that many of them 

 recognized the beaches as products of the lake, and they also 

 noted that the lake once discharged into the Des Plaines Valley. 

 Evidently these conceptions were entertained for many years 

 before any notice appeared in scientific publications. 



Bannister. — Probably the earliest scientific account of the 

 outlet is that given by Dr. H. M. Bannister in the Geology of Cook 

 County, published in 1868, as a part of the Geology of Illinois. 

 However, a report upon the survey of the Illinois River, by Col. 

 James H. Wilson and William Gooding, was published the same 

 year in the report of the U. S. Army Engineers, which makes ref- 

 erence to the former southwestward discharge of Lake Michigan. 

 Dr. Bannister opens his discussion of the old lake outlet and the 

 raised beaches with the following statement : 



"It is evident with a very little observation that at a compara- 

 tively recent period, subsequent to the Glacial epoch, a considera- 

 ble portion of Cook County was under the waters of Lake Michi- 

 gan, which at that time found an outlet into the Mississippi Valley 

 through the present channel of the Des Plaines." 



Dr. Bannister apparently makes no claim to discovery, as is 

 natural, in view of the fact that the outlet had been recognized as 

 such by residents for many years. 



Andrews. — One of the early publications of this Academy 

 presents a discussion of the beaches prepared by Dr. Edmund 

 Andrews, a publication which has attracted wide notice (i.) This 

 paper, however, deals mainly with the work of the lake at its 

 present stage. The ancient beaches are briefly discussed, but the 

 outlet is not described. A map accompanying the paper shows 

 the extent of the old lake beyond its present limit from the southern 

 end northward some distance into Wisconsin and Michigan. 



[11 The North American Lakes Considered as Chronometers of Poste:lacial 

 Time, bv Dr. Edmund Andrews, Trans, of Chicago Academy of Sciences. Vol II. 

 1870, Article 1, pp. 1-24. • 



