CORRELATION OF RAISED BEACHES 417 



mitted the wind to spread and otherwise modify them, makes it some- 

 what difficult to find enough data for accurate measurements. Never- 

 theless, enough was found to show that the shore-lines on both sides 

 of Green Bay correspond exactly to those on the Lake Michigan 

 border. 



THE ALGONQUIN SHORE-LINES 



The systematic variation in altitude of the highest shore-line of 

 Lake Algonquin can be seen by reference to the map. Here the 

 figures mark the altitude of the Algonquin beach or terrace at each 

 locality where it was measured with the spirit level. It is found by 

 experimentation that these points lie closely in harmony with a tilted 

 (or more accurately a warped) plane, on which the direction of steepest 

 ascent is about N. 15° E., and that of no differential uplift is about 

 N. 75° W. On Washington Island the highest Algonquin beach is 

 about 90 feet above Lake Michigan. When followed southward, it 

 is found to decline rather steadily until it is only 40 feet above the 

 lake at Sturgeon Bay (Fig. 4). Throughout this distance it is marked 

 either by a strongly cut terrace or by a well-built ridge of gravel or 

 chip stone. Above it there are no signs of submergence. Below it 

 several other shore-lines can be traced with equal distinctness. They 

 have similar warped attitudes, and represent successive later planes 

 of the lake, determined by repeated uplifts in its northern part. 



In Fig. 5 the warped planes are drawn in profile in the direction 

 of steepest inclination, N. 15° E. Each ordinate records a spirit- 

 level measurement of the crest of a beach ridge or the base of a cut 

 bluff, according to symbols which are explained in the legend. The 

 vertical scale is 500 times the horizontal, greatly exaggerating the 

 slope of the planes, and proportionately magnifying the discordance 

 of the ordinates. In view of this, and of the chance of discordance 

 due to {a) original variation in crest-line of the beaches and terraces, 

 (h) the error involved in determining the datum lake-level during days 

 when waves were running high, and (c) the error in leveling, which 

 probably amounts to a fraction of a foot, the accordance of ordinates 

 to the inferred planes of the highest Algonquin beach is remarkable. 

 Nearly all the ordinates lie within 3 feet of the plane ; and the few which 

 are 5 or 6 feet too high are all of them points which were regarded 

 at the time of their discovery as ridges built up to exceptional height 



