198 MINUTES OF MEETINGS. 



Lake Ontario. — 1st. Lockage of the Canal along the St. 

 Lawrence River, by the Canadian Surveys, 234^ feet. 2d. 

 Survey of the Oswego Canal, New York, 232 feet. Mean, 

 233i feet. 



Lake M'ie.—lst. Survey of the Erie Canal, in 1817, 561.20 

 feet. 2d. Lockage of the Erie Canal as constructed, from 

 the mitre sill at Albany to the mitre sill at Buffalo, 567 

 feet. 3d. Railroad survey — Catskill to Portland harbor, in 

 1828, 565 feet. 4th. By Capt. Williams' survey of the 

 Niagara Ship Canal, September 1834, assuming the Cana- 

 dian level 234^ feet for that lake, above Lake Ontario 328^ 

 feet— 563 feet. Mean, 564 feet. 



Lake St. Clair-— By S. W. Higgins' Geological Report of 

 Michigan, in 1840, 5 feet above Lake Erie; 564 and 5 equals 

 569 feet. 



Lake Huron.— By S. W. Higgins' Geological Report of 

 Michigan, in 1840, 13 feet above Lake Erie; 564 and 13 

 equals 577 feet. 



Lake Michigan, (southern extremity.)— By Railroad 

 Survey from Toledo to Michigan City, in 1851, (J. H. Sar- 

 gent, C. E.,) 18 feet above Lake Erie; 18 and 564 equals 

 582 feet. 



Lake Supei'ior. — 1st. By barometrical determinations of 

 Capt. Bayfield, in 1824, 624 feet. 2d. By measurement of 

 the rapids of St. Marys River, by A. Murray, Esq., of the 

 Geological Survey of Canada, in 1847, above Lake Huron 

 23 feet; 23 and 577 equals 600 feet. 3d. By survey of the 

 Bay de Noquet and Marquette Railroad, in 1859, 27 feet 

 above Lake Michigan ; 27 and 582 equals 609 feet. For this 

 lake the last, or No. 3, is much the closest approximation. 

 There are several sources of error, besides the "absence of 

 perfect accuracy in taking long levels, that may be the 

 cause of the above differences. 



The mean level of the lakes is never referred to in rail- 

 road and canal surveys, but always the surface of the water 



