446 J. W. SPENCER ^RELATIVE WORK OF TWO FALLS OF NIAGARA 



the efficiency down to 60, below which the loss through friction in the 

 inclined pipe and turbine was relatively still greater. But this me- 

 chanical contrivance,- using only about 70 cubic feet per second in a rela- 

 tively small pipe, can not be compared with the free flow of 10,000 cubic 

 feet per second, as in the case of the American Falls, where there is 

 neither tube friction nor turbine losses. 



The reason for comparing the relative work accomplished by the two 

 falls lies in the fact that throughout the greater life of Niagara the dis- 

 charge was more nearly like that of the American than of the Canadian 

 Falls. At that time the volume was three times as great as the present 

 American Falls, but the mean height of the uppermost cataract on 

 which the determinations were made was only seven-twelfths that of the 

 effective height of the American Falls; so that the work performed was 

 less than double that of the present smaller cataract. There is no sug- 

 gestion of any retardation in the lower river, but the lake level probably 

 held back the river so that there would be a pool at the foot of the falls 

 of a few feet in depth, as is commonly seen elsewhere; but the pool was 

 above the surface of the Medina sandstone and perhaps its depth may 

 not have exceeded 10 feet. At one time the river was well drained when 

 the lake was much lower than now, although later it backed up and 

 drowned the deeper channel described in "Evolution of the Falls of 

 Niagara." The basin below the main cataract now forms a safety balance, 

 as it were, being excavated to a depth according to the mechanical force 

 of the falls,^^ and it appears to me that a similar balance has always 

 maintained, else with the direct action on the bottom rocks, like at the 

 American Falls, the relative efficiency in erosion would be greater than 

 that of the Canadian Falls descending into its deep basin, thereby losing 

 much of its power. The frost action at the smaller falls, as pointed out 

 by Prof. James Hall, is greater than under a great sheet of water. 



Whether the work performed by the changing conditions of the Falls 

 of Niagara be within 10 per cent of that computed or require a correc- 

 tion of double this amount or more, the investigations give us an ap- 

 proximate result, based on direct measurements and not on mere opinions 

 or hypotheses. There now seem to be no important omissions in the 

 determination of the changing work of the falls. It was well to raise the 

 questions here discussed, and this paper is offered as an additional chapter 

 to the monograph on the Falls of Niagara, and the analysis of the feat- 

 ures here considered strengthens the conclusions previously reached. 

 They show that there is a balance maintained in the relative depth of the 

 pool beneath the retreating cataract. 



*i The variable depth of the river corresponds to the loss of erosion, as shown In the 

 work cited, pp. 344, 350, 351. 



