UNITED STATES LAKE SURVEY 



MONTHLY MEAN WATER LEVELS OF THE GREAT LAKES 



From OtficUl Rw^rdt, 1910 to dit«. 



Figure 0.— Levels of Lake Ontario. 23-year cycles. Note general subsidence about the sixth year, also approximate repetitions of features a, b. o, d. 



36923—36 (Face p. 104) 



