244 



MODIFICATION OF THE GREAT LAKES 



peated, and the difference found to be 18.470 feet, the point at 

 Sacketts Harbor having gone u]), as compared to the jioint at 

 Charlotte, 0.061 foot, or about three-fourths of an inch. Similarly 

 it was found that between 1858 and 1895 a point in Port Colborne, 

 at the head of the Welland canal, as compared to a jjoint in 

 Cleveland, Ohio, rose 0.239 foot, or nearly three inches. Between 

 1876 and 1896 a point at Port Austin, Michigan, on the shore of 

 Lake Huron, as compared to a point in Milwaukee, on the shore 

 of Lake Michigan, rose 0.137 foot, or one and one-half inches; 

 and in the same period a point in Escanaba, at the north end of 

 Lake Michigan, as compared to the same point in Milwaukee, 

 rose 0.161 foot, or about two inches. 



There is no one of these determinations that is free from doubt ; 

 buildings and other structures on which the benches were markt 

 may have settled, mistakes may have been made in the earlier 

 leveling, when there was no thought of subjecting the results to 

 so delicate a test, and there are various other possible sources of 

 error to which no checks can be applied ; but the fact that all 

 the measurements indicate tilting in the direction predicted by 

 theory inspires confidence in their verdict. This confidence is 

 materially strengthened when the numerical residts are reduced 

 to a common unit and compared. 



Summary of Distances, Time Intervals, and Measurements of Differential 

 Earth Movements 



Mean 41 



Weighted mean 42 ± .05 



