SURFACE LEVELS OF THE GREAT LAKES CURVES OF ANNUAL MEANS OF EACH LAKE FROM 1860 TO 1910. YEARS. Levels in feet above Mean Tide Under direction of Brigadier General W. H. BIXBY, Chief of Engineers, Washington, D. C., November, 1911 Drawn in Office of US Lake Survey. Based upon Records of the Lake Survey and other US Engineer Offices. + 2 ± 0 2 |