THE RIVERS AND THE ICE-FLOES. 15 



with groves, while the latter are usually heavily 

 timbered. 



Again, other rivers, having their sources within Brit- 

 ish territory, flow northwards, and debouch in the 

 Arctic Ocean, after traversing hundreds of miles of 

 desert solitudes. Of these, the chief are the Youkon, 

 the Turnagain or Liard's River, and the Mackenzie. 

 The last flows out of the north-west corner of the 

 Great Slave Lake, and carries with it almost to its 

 debouchure a milder climate than prevails in the- re- 

 gions contiguous to its course. Thus along its banks 

 timber of larger growth is found than is elsewhere 

 yielded by the sterile and frost-bound soil ; for here 

 the ground is ever frozen, the summer heats not pene- 

 trating more than a few feet beneath the surface. The 

 winter cold often reaches 40 and even 50 below zero, 

 while the heat in summer, on the other hand, rises to 

 100 in the shade ! 



At the junction of the Liard with the Mackenzie, 

 in latitude 61 north, is situated Fort Simpson, a post 

 of the Hudson Bay Company ; and in spring, when the 

 ice breaks up in the rivers, a scene at once grand and 

 terrible is witnessed by the inhabitants. Among the 

 Rocky Mountains to the south the Liard has its source; 

 and swollen by the melting of the snows on the hills, 

 it rushes impetuously northwards, pouring its foaming 

 flood into the still ice-bound Mackenzie. For a short time 

 the ice resists the action of the waters, but soon gives 

 way with a crash like thunder. Roaring and tumbling 



