6o 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 94 





I860 1861 



pUprpf 



1865 1866 





£ - \ .0\N r.A\R / 



33 I I884~ 



ij£ti 



1885 I 1836 



2 -.5 , i^iil 



UNITED STATES LAKE SURVEY 



MONTHLY MEAN WATER LEVELS OF THE GREAT LAKES 



From Official Records, 1910 to dale. 



Fig. 25. — Levels of Lake Ontario, 23-year cycles. Note general s 



