41 8 JAMES WALTER GOLDTHWAIT 



by storm- waves in places of unusual exposure. A great barrier ridge 

 at Egg Harbor, for instance, which was built in 60 feet of water across 

 the head of a bay, has a crest 7 feet higher than the cut terrace from 

 which it tails out. The terrace corresponds closely to the inferred 

 Algonquin plane; and a distant beach ridge lies at the same level 

 just below the top of the barrier embankment. The discordance of 

 this ordinate, like the two or three others, is wholly within expectation. 



It is seen that this reconstructed plane slants southward from 

 Washington Island at about i ^ feet per mile to Sturgeon Bay (slightly 

 more in the northern part and less in the southern part), and that it 

 suddenly becomes flatter near Sturgeon Bay and slants southward 

 at the rate of about 8 inches per mile to Two Rivers, where it is 

 nearly, if not quite, horizontal. For long distances south of Sturgeon 

 Bay the Algonquin shore-line has been cut away during later stages ; 

 but the extinct flood-plains, now terraces, are found at appropriate 

 heights in most of the stream valleys. 



Two lower Algonquin planes, marked on Washington Island and 

 near Death's Door by deeply cut terraces, can be traced southward 

 in a similar way, converging slightly in that direction until at Sturgeon 

 Bay they are so close together as to be difficult to identify separately. 

 Ordinates which lie between the planes and mark weaker beaches 

 suggest short-lived stages of intermediate age. In only one case 

 (plane A') has an attempt been made to reconstruct these less dis- 

 tinct planes. 



THE NIPISSING AND LOWER SHORE-LINES 



Below the slanting and diverging Algonquins is a nearly horizontal 

 plane which is marked everywhere, and more strongly than any other 

 (see Fig. 3). From 22 feet above the lake at Washington Island this 

 declines almost imperceptibly to about 16-18 feet at Two Rivers — a 

 drop of only 4 or 6 feet in a distance of about 90 miles. The remark- 

 able strength of this shore-line — usually a high-cut bluff and broad 

 terrace — together with its correspondence in altitude with the Nipis- 

 sing shore-line traced by Taylor in the northern part of the Great 

 Lake region down to Gladstone and Escanaba (just north of the 

 eastern Wisconsin district), leaves little doubt that it marks the Nipis- 

 sing plane, a stage of the lakes when both the North Bay outlet and 



