TITLES AND ABSTRACTS OF PAPERS 35 



Lake Agassiz, and cover also, with similar fullness, the lower shorelines, whose 

 tracing was not attempted by Upham. 



Presented in full without notes. 



Discussion 



Dr. R. D. Salisbury : I should like to ask Mr. Leverett how accurately the 

 water level of an extinct lake can be determined at any given point? May 

 not the level taken be a beach several feet above the lake or a bar several feet 

 below? If so, would this not account for apparent local irregularities in rise? 



Prof. A. P. Coleman : One can not expect to find a rise corresponding to 

 the relief of load from the removal of every lobe of the ice. One would expect 

 the earth's crust to respond only in a general way to the relief of load, and 

 we actually find elevation only where ice once existed. 



Further remarks were made by Dr. J. W. Spencer, and Mr, Leverett 

 replied. 



TIME MEASURES IN THE NIAGARA GORGE AND THEIR APPLICATION TO 

 GREAT LAKE HISTORY 



BY FRANK B. TAYLOR 



(A'bstract) 



The time estimates for the five sections of the Niagara gorge are as follows, 

 the first or oldest being placed at the bottom : 



Fifth section : Upper great gorge 3,000 to 3,500 years 



Fourth section : Gorge of the Whirlpool Rapids. 5,000 to 8,000 



Third section : Lower great gorge 2,500 to 3,000 " 



Second section : Old narrow gorge 8,000 to 13,000 *' 



First section : Lewiston Branch gorge 1,500 to 3,000 " 



These estimates are, as here shown^ merely approximations between fairly 

 wide limits. The time for the making of the whole gorge is believed to lie 

 somewhere between the totals of the two columns ; or, in round numbers, 

 between 20,000 and 30,000 years. The uncertainties of the time estimates for 

 the two narrow sections — the second and the fourth — both of which were 

 made with only 15 per cent of Niagara's present volume, introduces a possible 

 necessity of extending the time a few thousands of years, but probably not 

 more than 5,000 years at the greatest. This possible necessity is regarded as 

 remote rather than probable. 



On the basis of these time estimates for the different sections of the gorge 

 the correlative stages of the Great Lake history were reviewed, the main 

 object of the paper being to describe the conditions of the lakes during the 

 making of each gorge section and to point out the principal features then 

 made, the time taken for the making of these features, and the time during 

 which they have since been exposed to weathering and erosion. 



The distribution in time of the uplifts which have affected the Great Lakes 



