38 TRANSACTIONS OF THE CANADIAN INSTITUTE. [VOL. V. 



Superior 60 ly^^ feet. The difference of 20^ feet between lakes Superior 

 and Huron, occurs in the rapids of St. Mary's River ; the 8yV feet be- 

 tween lakes Huron and Erie, mainly in the Detroit River. The difference 

 of 326 feet between lakes Erie and Ontario occurs in the vicinity of 

 Niagara Falls, and is principally grouped as follows : — 100 feet in the 

 five miles of rapids between Lewiston and the lower suspension bridge^ 

 10 feet in the rapids between the bridge and the Falls, 160 feet at the 

 Falls, 50 feet in the rapids immediately above the Falls, and six feet in 

 the Upper Niagara River. 



The mean depth of Lake Superior is about 475 feet, the deepest point 

 marks a depth of 1008 feet, or 406 feet below the level of the sea. Lake 

 Huron has a mean depth of about 250 feet, and a maximum depth of 

 750 feet. Lake Michigan has a mean depth of 325 feet, and a maximum 

 depth of 870 feet. Lake Erie is comparatively shallow, having an average 

 depth of less than 70 feet, and a maximum depth of 210 feet. Lake 

 Ontario has a mean depth of about 300 feet, and a maximum of 738, or 

 nearly 500 feet below sea level. The channels of the rivers connecting 

 the lakes seldom exceed 50 feet. According to the U. S. lake surveys^ 

 the mean annual rain and melted snowfalls of the several lake basins are 

 as follows : — Lake Superior, 29 inches; Lake Huron, 30 inches; Lake 

 Michigan, 32 inches ; lakes Erie and Ontario, 34 inches. This is about 

 equal to 31 inches on the entire lake basin. The following represent the 

 average discharges at the outlets of the lakes : — 



Lake Superior at St. Mary's River, 86,000 cubic feet per second. 



Lakes Michigan and Huron at St. Clair River, 225,000 " " 



Lake Erie at Niagara, 265,000 " " 



Lake Ontario at St. Lawrence River, 300,000 " " 



" It is well understood that the principal factors on which the stage of 

 water in the great lakes depends, are the rain and snowfalls, the evapora- 

 tion, and winter temperature ; the rain and snowfalls furnish the supply,, 

 the evaporation withdraws a part before it reaches the mouths of the 

 streams, and form the surfaces of the lakes ; a severe and continued cold 

 winter preventing the melting of the snow, will raise the summer stage at 

 the expense of the winter stage. The region of the great lakes is so vast 

 that the conditions of rainfall, evaporation and temperature may vary 

 widely in different sections." 



The following is a detailed statement of the rain and snowfall from 

 1854 to 1893, and the highest and lowest water on Lake Ontario : 



