46o JAMES WALTER GOLDTHWAIT 



beaches around the south end of Lake Michigan are still horizontal, 

 having been undisturbed by earth movements since they were formed, 

 those in the more northerly portions have been affected by repeated 

 differential uplifts. Each beach rises northward at a rate different 

 from those above and below it, and at a rate which increases repeatedly 

 in a northward direction. At one or more points, the planes marked 

 by the inclined beaches split, vertically, so that a single stage in the 

 southern part of the lake represents fifteen or twenty stages in the 

 northern part. This is the result of the repeated tiltings of the 

 northern district. The problem of proper correlation of the frag- 

 ments, then, and of the complete reconstruction of the old water 

 planes is a very difficult one. Not only must as many of these frag- 

 ments as possible be discovered, but at each locality every beach and 

 terrace of the series must be noted, its strength and peculiar charac- 

 ters recorded, and its altitude measured with all possible precision. 

 The raised beaches about the south end of Lake Michigan have 

 been described in detail by Leverett,' Alden,^ and others. The 

 beaches along the west side of the lake, in eastern Wisconsin, were 

 first studied in detail by the present writer,^ in 1905. The planes 

 which were recognized there have since been traced farther north 

 in the upper peninsula of Michigan, by Hobbs.^ On the east side of 

 the lake, Taylor and Leverett have for several years been accumu- 

 lating detailed information concerning the beaches. It was with the 

 purpose of supplementing this work by a series of more detailed and 

 precise measurements, and thus establishing more definitely the 

 identity of certain beaches, and their relations, that the writer, under 

 Mr. Taylor's direction, undertook a six weeks' survey of the shore 

 lines along the east side of Lake Michigan in July and August, 1907, 



1 Frank Leverett, "The Illinois Glacial Lobe," U. S. Geol. Surv. (Monog. 

 XXXVIII), 1899; also earlier papers (see op. cit., p. 419). 



2 W. C. Alden, "Chicago Folio," Geologic Atlas of U. S., U. S. Geol. Surv., Folio 

 81, 1902; "The Delavan Lobe of the Lake Michigan Glacier of the Wisconsin Stage 

 of Glaciation, and Associated Phenomena," U. S. Geol. Surv. (Prof. Paper 34), 1904; 

 "Milwaukee Special Folio," Geologic Atlas of U. S., U. S. Geol. Surv., Folio 140. 1906. 



3 J. W. Goldthwait, "Correlation of the Raised Beaches on the West Side of Lake 

 Michigan," Jour. Geol., Vol. XIV, pp. 421-24, 1906. "Abandoned Shore-Lines of 

 Eastern Wisconsin," Wis. Geol. &° Nat. Hist. Surv. (Bull, xvii), 1907. 



4 For the Mich. Geol. Surv. Results not yet published. 



