1908.] 



PHYSICAL GEOGRAPHY LIARD RIVER VALLEY. 



31 



The climate of the Liard River Valley, like that of the Peace, 

 varies widely in the different sections. The upper pari of the river, 

 lying west of the mountains, enjoys a climate much tempered by the 1 

 warm Pacific winds. The upper Nelson River also, the principal 

 tributary of the Liard east of the mountains, lies far to the southward 

 and sufficiently near the Pacific to come within its modifying influ- 

 ence. Unfortunately no exact data regarding the temperature of the 

 upper Liard or the Nelson are at hand; hence the conditions there 

 can not he compared directly with those on its lower course. The 

 average temperature conditions on the lower Liard may be fairly 

 represented by those taken at Fort Simpson in 1000. given on page 34. 

 The warm westerly winds which reach the valley of the Liard extend 

 their influence as far as its mouth and have been known to cause a 

 pronounced thaw there even in January, the coldest month. This 

 modifying influence is apparent in the character and progress of 

 vegetation, the migration of birds, and in other phenomena. It 

 is especially manifest, however, in its relation to the breaking up 

 of the river and the attendant effect on the conditions along the banks. 

 Furthermore, the disruption of the Liard ice starts that in the 

 Mackenzie also, which thus opens considerably earlier than would be 

 the case were it not affected by its warmer tributary. This, of course, 

 has its natural effect in accelerating the progress of vegetation on the 

 banks of the Mackenzie below the Liard. 



The following table shows the dates of the opening and closing of 

 the Nelson at Fort Nelson during: a series of vears: 



Dates of opening and rinsing of Nelson River at Fort Nelson. 



The following table shows the dates of the closing of the Liard at 

 Fort Liard during a series of years: 



Dat<« of closing of Liard River at Fort Liard. 



The dates of the opening of the Mackenzie at the mouth of the 

 Liard during a series of years appear in a table given on page 36. 



At Fort Liard the river is said to break up generally about the 1st 

 of May. The approximate dates for the years given may be ascer- 



