358 MODIFICATION OF GREAT LAKES BY EARTH MOVEMENT. 



the old light-house in Charlotte was then 18.53 L feet above a certain 

 point on the Masonic Temple in Sacketts Harbor. In 189G the measure- 

 ment was repeated, and the difference found to be 18.470 feet, the point 

 at Sacketts Harbor having gone up, as compared to the point at Char- 

 lotte, 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 point in Cleveland, Ohio, rose 

 0.239 foot, or nearly 3 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 1£ 



Sandusky 



Fig. 7. " 



MAP OF THE GREAT LAKES, SHOWING PAIRS OF GAGING STATIONS AND ISOBASES OF OUTLETS. 

 The isobases are marked by full lines. Broken lines show the pairs of stations. 



inches; and in the same period a point in Escauaba, at the north end 

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

 0.161 foot, or about 2 inches. 



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

 buildings and other structures on which the benches were marked 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 

 results are reduced to a common unit and compared. 



