GEOLOGICAL AND NATURAL HISTORY SURVEY. 19 



this beach distinguishes it so strikingly from the paucity of life 

 which characterizes the other beaches that a suspicion of a dif- 

 ferent 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 temporary 

 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 the Johnson 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, (i.) 



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

 lies in the occurrence of phenomena immediately south of the 

 ridge, which will demonstrate that the water stood at a level suf- 

 ficiently high to have caused outflow through 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 

 also seems to be sustained by very weak evidence. 



Prof. L. E. Cooley has called my attention to rapids at the 

 head of St. Clair River, which he thinks may have a bearing upon 

 the lowering of the lake level a few feet in recent geological times. 

 For several miles the St. Clair River has a fall of about 16 inches 

 per mile, making nearly all the descent of nine feet which is made 

 between Lake Huron and Lake Erie. This rapid portion is stated 

 by Professor Cooley to be cutting glacial drift, and it is his opinion 

 that this drift barrier may have at one time held the lake level even 

 as high as the second beach. The matter is one worthy of investi- 

 gation, and Professor Cooley has hoped to give it fuller attention. 

 The question of the date of this beach and of its relation to uplifts 

 and barriers must therefore be left open until more substantial 

 evidence is gathered. 



THE PBESENT BEACH OF LAKE MICHIGAN. 



Dr. Edmund Andrews has discussed the present beach of 

 Lake Michigan in his paper published in an early volume of the 

 Transactions of this Academy, and compared its strength with that 

 of the beaches of Lake Chicago (2). Since this paper is now out of 



Cl) Proc. A. A. A. S., Brooklyn Meeting, 1894, pp. 242-243. 



(2) Trans. Chicago Academy of Sciences, VoL II, 1870, pp. 1-23. 



