Science, Geology and Physics 



is known to the writer. So also the rate of rise of the earth's 1898 

 crust throughout the lake region, and the consequent hypothesis pcncer 

 announced at the same time that the Falls of Niagara would 

 probably cease to exist in the near geological future, owing to 

 the diversion of the waters the four upper Great Lakes to the 

 Mississippi by way of Chicago, was first announced by the 

 writer in 1894. 1 This has been confirmed by the subsequent 

 researches of Prof. G. K. Gilbert, 2 with almost identical results 

 when reduced to the same standard. In his paper (p. 602) 

 Prof. Gilbert says : " So far as I am aware this paper broaches 

 for the first time the idea of the differential elevation of the lake 

 region, and it contains the only observations that have been cited 

 as showing the recent changes of that character. In late years 

 the subject has been approached from the geologic side, and 

 Dr. J. W. Spencer has expressed his opinion that the warping 

 or tilting of the whole region is now in progress." From the 

 standpoint of measuring the changes of level of the lake waters, 

 I believe that Prof. Gilbert is correct in his claim, but they only 

 confirm the correctness of the previous geological determinations. 

 The tilting of the beaches has been measured by several of us, 

 but the direction of the tilting was determinable only after my 

 surveys on the Canadian side of the lake enabled us to triangulate 

 the direction of the rise, and in my papers between 1888 and 

 1891 this determination of the direction of the rise was calcu- 

 lated and shown only to be confirmed by all subsequent measure- 

 ments, including the recent paper of Prof. Gilbert. But the diffi- 

 culty awaiting us was that we did not know the rate of warping, 

 for, if found for one district, it could be calculated for the whole 

 lake region. Of course it was not an absolute rate of rise, but the 

 differential rise of the lake region. However, I found that during 

 the last 1 500 years the mean rise in the Niagara district was 

 from 1 J/4 to 1 J/2 feet per century, as compared with Chicago. 



1 Am. Jour. Sci., XLVIII, pp. 455-72, 1894. 



2 1 8th Ann. Rep't U. S. Geol. Surv., p. 639, 1 898. 



39 609 



