COUNTRY WEST OF LAKE SUPERIOR. 



21 



1. The mean minimum level is attained in January or 

 February. 



2. The mean maximum level in June. 



3. The mean annual variation is 25 inches. 



4. The maximum variation in twelve years is 4 feet 6 

 inches. 



5. There is no periodicity observable in the fluctua- 

 tion of the lakes, and recent observations tend to show 

 that there is no flux and reflux dependent upon lunar 

 influence.* 



The Bishop of Montreal states in his journal that it is 

 only during an extraordinary concurrence of circum- 

 stances that the whole of Lake Superior can freeze over.f 

 He was assured that this remarkable event happened in 

 the winter of 1843, after a calm of four days, and during 

 intensely cold weather. No other instance is said to be 

 on record. 



The greatest supposed depth of Lake Superior is 1200 

 feet. Its area is about 32,000 square miles, its coast line 

 about 1,500 miles, and it contains probably 4,000 cubic 

 miles of water. 



The barrier which opposes further progress by steam 

 or boat navigation westward of Lake Superior follows 

 the general direction of the north-western and western 

 coast of that lake. Near Fond du Lac, in the territory 

 of the United States, the dividing ridge separating the 

 valley of Lake Superior from that of the Mississippi, is 

 distant from the St. Louis Eiver about 18 miles in a 

 southerly direction, and here the elevation of the ridge is 

 475 feet above the waters of the lake. 



* Chas. Whittlesey and C. Dewey. American Journal of Science and 

 Arts, May 1859. 



t Journal of the Bishop of Montreal during a visit to the Church Mis- 

 sionary Society's North West American Missions. 



c 3 



