THE PRESENT BEACH OF LAKE MLCHIGAN. 453 



Indeed, the abundant life of the waters which formed this beach distinguishes 

 it so strikingly from the paucity of life which characterizes the other beaches 

 that a suspicion of a different origin at once arises. 



Dr. J. W. Spencer has advanced the view that an uplift at the Niagara 

 outlet is still in progress, and has suggested that the recession of the falls 

 of Niagara past Johnson's Ridge, a ridge standing higher than the remainder 

 of the gorge and situated about a mile north of the falls, would have caused 

 a temporaiy partial discharge of the upper lakes, including Lake Erie, into 

 the Mississippi, a discharge which did not stop the outflow by Niagara. He 

 maintains that when Niagara Falls had effected the incision through John- 

 son's Ridge, the level of Lake Erie fell about 24 feet, reaching a level 17 

 feet below the Chicago divide, and thus the full flow of the outlet was 

 returned to Niagara. 1 



The test of the value of Dr. Spencer's ingenious suggestion lies in the 

 occurrence of phenomena immediately south of Johnson's Ridge, which will 

 demonstrate that the water stood at a level sufficiently high to have caused 

 outflow from the Chicago Outlet. Such a stage of water should have left 

 shore markings there as well as on the plain at the head of Lake Michigan. 

 The view that an uplift is still in progress in the vicinity of the Niagara 

 outlet is apparently sustained by recent evidence brought out by Mr. G. K. 

 Gilbert. 2 The question of the date of. this beach and of its relation to 

 uplifts and barriers ought, however, to be left open until more complete 

 evidence is gathered. 



THE PRESENT BEACH OF LAKE MICHIGAN. 



Dr. Edmund Andrews some years ago discussed the present beach of 

 Lake Michigan and compared its strength with that of the beaches of Lake 

 Chicago. 3 Since his paper is now out of print and copies of it are difficult 

 to obtain, some of the computations there made are presented below. Dr. 

 Andrews apparently includes the beachlets between the Tolleston beach 

 and the shore of Lake Michigan, referred to above, in the present lake stag*e. 



The lake is generally encroaching upon the district on its west border 

 from the Wisconsin line southward to Chicago, though piers built along the 

 shore in Chicago, and for some distance northward, now prevent further 



1 Proc. Am. Asso». Adv. Sci., Brooklyn meeting, 1894, pp. 242, 243. 



2 Nat. Geog. Mag., Sept., 1897, pp. 233-247. A fuller discussion has been presented by Gilbert in 

 the Eighteenth Annual Report of this Survey, Part II, pp. 595-647, issued in 1898. 



3 Trans. Chicago Acad. Sci., Vol. II, 1870, pp. 1-23. 



