19US.] 



PHYSICAL GEOGRAPHY GREAT SLAVE LAKE. 



29 



These temperatures for Hay Eiver, however, are not strictly rep- 

 resentative of Great Slave Lake, since this post is situated at the 

 mouth of a large river which heads far to the southwestward, a fact 

 which probably considerably influences the climate at its mouth. 

 The temperature conditions at other points on the southern shores of 

 the lake probably do not differ materially during an average year 

 from those here recorded. On the Northern and Eastern arms, 

 however, the spring and autumn temperatures are considerably lower. 

 The winters are severe and the conditions recorded at that season 

 by the thermometer are intensified by high winds which sweep over 

 the surface of the lake and in the autumn keep it from freezing- until 

 a late date. Ice forms to a considerable thickness and persists until 

 midsummer. I have no exact data regarding the time of the freezing 

 and breaking up of the ice during a series of years, but the dates 

 given by McConnell (loc. cit.) probably represent about the average 

 time. lie says: 



Ice forms in the bays and along the shores of Great Slave Lake between the 

 20th and tbe last of October, and the whole lake is usually fast by tbe middle 

 of November." The ice attains a thickness of from six to eight feet, in the 

 spring tbe disruption of tin ice takes place about the 1st of July, but sometimes 

 occurs as early as the 20th of June and as late as the 10th of July. 



Ill the main or western part of the lake the ice breaks up earlier 

 than in the eastern part. At Fort Rae, according to Russell, it dis- 

 appears earlier than in the main body of the lake. The following 

 table was compiled by him from the journals kept at the Hudson's 

 Bay post: 



Dates of breaking up and setting of ice in the Northern Ann at Fort Rae. 



After the disruption of the ice the floes are'tossed back and forth 

 by the winds until finally they become disintegrated. In 1903 a little 

 ice still remained about the western end of the lake until July 1. and a 

 week earlier the Wrigley, crossing from the outlet to Fort Resolution, 

 had made its way with difficulty among the drifting floes. In the 

 eastern part of the lake the ice does not entirely disappear in some 

 seasons until late in June. 



°The renter of the lake lias been known to remain open until the 1st of 

 December (fide Richardson). 



