ANCIENT WATER-PLANES AND CRUSTAL 

 DEFORMATION 



H. H. ROBINSON 

 Yale University, New Haven, Conn. 



In a recent bulletin of the Wisconsin Geological Survey,' Gold- 

 thwait has presented the results of an interesting study of the strands 

 of the ancient Great Lakes as they occur in eastern Wisconsin. The 

 field-work is much more detailed and accurate than the average, and 

 the success in reconstructing the complex series of shore -lines of Lake 

 Algonquin, in the region studied, is largely the result of using a wye 

 level, instead of a hand level, or aneroid barometer, in determining 

 the heights of the ancient beaches and terraces above the present lake 

 level as a datum plane. 



By far the greater part of the report is devoted to the descriptions 

 of the old shore-lines and a review of previous work. And the con- 

 clusions on p. 42 bear only on the history of the ancient Great Lakes. 

 In chap, iv, however, the author takes up the question of the deforma- 

 tion of the Great Lakes region and presents a new hypothesis as to the 

 character of the crustal movements which have deformed the ancient 

 shore-lines. 



The hypothesis in brief is: that tilting of the earth's crust took 

 place on the north side of axes which moved northward at intervals, 

 resulting in the originally horizontal Algonquin beach-lines being 

 given a broken profile with progressively steeper slopes northward. 

 The movement was such as to tilt the surface of any block without 

 warping. The idea expressed, it will be seen, is more definite than that 

 of the older hypothesis of "differential warping" and may be spoken 

 of as "differential tilting." 



In this article it is desired to analyze the data upon which these 

 hypotheses rest in order to form some idea as to their probable error, 

 and also to compare the two hypotheses in order to see which is the 



I J. W. Goldthwait, "The Abandoned Shore-Lines of Eastern Wisconsin," Wis- 

 consin Geological and National History Survey, Bull. No. XVII, Sci. Ser., No. 5, 1907. 



347 



