BULLETIN OF THE GEOLOGICAL SOCIETY OF AMEfilCA 

 Vol. 21, pp. 441-446 AUGUST 10, 1910 



EELATIVE WORK OF THE TWO FALLS OF NIAGARA 



BY J. W. SPENCER 



{Read before the Society December 29, 1909) 



CONTENTS 



Page 



Preface 441 



Rate of recession of the American falls 441 



Relative efficiency of the two falls of Niagara 443 



Preface 



The special interest in the Falls of Magara, apart from the scenic and 

 economic, lies in two scientific directions. One of these is connected with 

 the researches into the remarkable physical changes, not onl}^ of the direc- 

 tion of the drainage of the upper lakes, but of the whole lake history and 

 the production of the falls themselves. Although these questions are pri- 

 marily American, the opportunity is better afforded here than elsewhere 

 of studying the physico-geological problems involved, and hence the falls 

 are of general concern. The other interest is that connected with the age 

 of the falls, as they furnish the best measurements of the amount of geo- 

 logical work that has been performed in a given time, thus becoming a 

 chronometer which, when brought into comparison with the work effected 

 in other localities, will enable us to have definite ideas of glacial time. 

 In this respect the subject is of world-wide interest. Any reasonable 

 variation suggested can only lead to more precise results. To two minor 

 omissions in my previous treatment of the past recession of the Falls of 

 Niagara^ Dr. 0. K. Gilbert has called attention, namely, the work of the 

 American cataract and the variation in the relative effective work of the 

 two falls. These questions^ I have since partly considered.^ 



Rate op Recession of the American Falls 



For want of sufficient time and opportunity and on account of my im- 

 pression of the relative unimportance of the smaller cataract, I gave but 



1 J. W. Spencer : The Falls of Niagara ; their evolution and varying relations to the 

 Great Lakes ; characteristics of the power and effects of its diversion. Geological Sur- 

 vey of Canada, 1C07, pp. xxxi, 490, with maps and illustrations. 



2 Science, vol. xxvlil, 1908, pp. 754-759. (441) 



;SXXI— Bull. Geol. Soc. Am., Vol. 21, 1909 



