Temperatures of Great Lakes and St. Lawrence, 70 



in 38 and 45 fathoms it was 52° F. The Southern basin not 

 only lies in a lower latitude, but is much shallower and has 

 a bottom largely composed of sand. Apart from these cir- 

 cumstances, the natural flow of the warm Michigan surface 

 waters is towax'ds and into this basin before their final 

 entrance into the St. Clair River at Sarnia. On the other 

 hand, the tendency of the colder Superior waters constantly 

 flowing into the Central basin and modifying the warm sur- 

 face waters from Lake Michigan, is to maintain a somewhat 

 lower temperature in the depths of the Central than in the 

 lesser depths of the Southern basin 



In their main expanse, Lake Superior and the Georgian 

 Bay thus constitute in midsummer, great bodies of colder 

 water, whilst the Central basin of Lake Huron in its 

 greater depths also forms a reservoir of cold water, but 

 tempered by the warmer inflow from Lake Michigan. 



Lakes Erie and Ontario are, on the other hand, warmer 

 lakes, consequent on their geographical position, their 

 affluent streams from the south and south-west, and the 

 necessarily higher temperature of the larger volume of 

 waters which have flowed over the great shallows of Lake 

 St. Clair before reaching Lake Brie. 



Records of observations made by myself during this last 

 summer near the outlet of Lake Ontario, and in the St. 

 Lawrence and other rivers, and by Staff-Commander 

 Boulton, R.N., during last and previous seasons in the 

 Georgian Bay, appear to establish some interesting results 

 which are here appended. It is not assumed that these 

 results are new, but they exemplify some characteristics of 

 fresh water in the great masses in which it occurs in the 

 Canadian Great Lakes and rivers, and under the varying 

 conditions of climate which the geographical position of 

 these lakes and rivers presents. 



The instruments used in my observations were : — for sur- 

 face readings, Negretti & Zambra's Reference Thermometer 

 with Kew corrections, and, for deep water, the same 

 makers' Patent Marine Thermometer, carefully compared 

 with standard instruments. Staff-Commander Boulton's 



