470 J. W. Spencer — Duration of Niagara Falls. 



have been raised up since the birth of Niagara Falls. Of this 

 latter amount about 130 feet have been lifted since the waters 

 were turned into the Niagara drainage. Again we get some 

 proportions. 



The ratios of the deformation of the Lundy and Iroquois 

 beaches are about the same, and we have the Lundy beach dif- 

 ferentially raised 160 feet in the Niagara district, and the 

 Iroquois beach deformed to 370 feet near the outlet of Lake 

 Ontario (compared with the level at the head of the lake) 

 since the close of the Iroquois episode. And here there are 

 data for comparison. These figures have been mostly taken 

 from the papers already cited. Compiling the results derived 

 from all these data, it appears that : 



A. The time which has elapsed since the Iroquois episode, 



or the end of the first episode of the falls is : 



(1) From the computations given 13,800 years. 



(2) From the date of deformation recorded in 



the Iroquois beach* 14,800 " 



(3) From the deformation recorded in the 



Lundy beachf 12,800 " 



Mean result 13,800 " 



B. (1) Computed time since the Huron waters 



turned into the Niagara 7,800 " 



(2) From the proportional deformation of the 



Algonquin (N.E.) outlet compared with 



the computed age of the riverj 7,400 " 



(3) From the proportional deformation of the 



Algonquin uplift § 6,500 " 



Mean result 7,233 " 



C. (1) Computed age of Niagara river 32,000 " 



(2) From the rate of deformation of Algonquin 



beach since the commencement of Niagara 



riverfl 28,000 " 



Mean result... 30,000 " 



These computations were originally made not to seek for 

 favorable evidence but to discover discrepancies, for I did not 

 expect that the date had been correlated with sufficient accur- 

 acy ; but the several results agreeing so closely in spite of the 

 unavoidable inaccuracies, seem to me to comfirm the general 

 correctness of the determinations of the phenomena and the 

 methods of computation. . - 



* A differential rise of 370 feet at the outlet of Lake Ontario divided by 2-5 

 feet a century. 



f A rise of 160 feet in the Niagara district divided by T25 feet a century. 



% if£ of 32,000 years. 



§ if of 28,000 (see next note). 



|| Rise of 660 feet in the Algonquin beach less 100 feet before the birth of the 

 Niagara at the rate of 2 feet a century. 



