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NATURALIST'S GUIDE TO THE AMERICAS 



from the Pacific sometimes exert a 

 decided though temporary influence 

 on the climate of the Mackenzie, and 

 the Liard, opening early, disrupts the 

 Mackenzie ice below the confluence. 

 The removal of the icy covering of an 

 immense river and the blending with its 

 flood of the waters of a warmer tributary 

 necessarilj' afi"ect conditions along its 

 banks. The ice in the Liard, having 

 broken its bonds, is forced against that 

 of the Mackenzie, through which it 

 opens a passage, and urged on by the 

 immense pressure behind it breaks its 

 way seaward, occasionally becoming 

 dammed and raising the level of the 

 water until the increased pressure again 

 clears a channel. At Fort Simpson, 

 near latitude 62°, the ice continues to 

 drift in quantity for some days after 

 its disruption. About ten days, on 

 the average, after the Mackenzie opens 

 at this point, or about the time that the 

 breaking ice has reached latitude 65°, 

 the upper Mackenzie opens and the 

 channel is filled again with floating ice. 

 Sometimes a third consignment of 

 floes, from the "Little Lake" or from 

 Great Slave Lake, fills its current. 



Records of the opening and closing 

 of the Mackenzie at Fort Simpson, kept 

 between 1876 and 1906 (but not con- 

 tinuously) show that the river usually 

 broke up between May 5 and 10 (ex- 

 treme dates April 29 and May 14), 

 and closed usually about November 20 

 ^extreme dates November 17 and No- 

 vember 28). At the mouth of Bear 

 River the Mackenzie usually opens 

 between May 15 and 20 (extreme dates 

 May 9. and May 28 J, and closes about 

 November 10 (extreme dates November 

 2 and November 18). 



Seasonal phenomena in Mackenzie 

 Valley, 1903-1904: Following is a brief 

 account of the progress of the seasons 

 and attendant phenomena as observed 

 by the writer from October 1, 1903, 

 to July, 1904. The first three weeks in 

 October were spent in ascending the 

 Mackenzie from Fort Norman, at the 

 mouth of Bear River, to Fort Simpson, 

 at the mouth of the Liard. The fact 



that these notes were taken while the 

 party was traveling detracts but little 

 from their value, since the conditions 

 in different parts of this stretch of river 

 were nearly uniform at that time. The 

 period from October 20, 1903, to June 1, 

 1904, was spent at Fort Simpson, and 

 the month of June in descending the 

 Mackenzie to its delta. 



When the Mackenzie was reached, on 

 September 30, 1903, by descending Bear 

 River, a marked contrast was noted 

 between the conditions left behind at 

 Great Bear Lake and those encountered 

 on the Mackenzie. The temperature 

 was considerably higher, and several 

 species of small birds which had practi- 

 cally disappeared from Great Bear Lake 

 were common. The high mountains to 

 the west of the Mackenzie were covered 

 with snow. 



During the first few daj^s of October, 

 as we were ascending the Mackenzie, 

 the weather was mostly fine, with south- 

 erly winds part of the time. The nights 

 were frosty and ice formed on still 

 water. The blue flowers of a gentian 

 (apparently Gentiana acuta), the latest 

 flowers observed, were seen on October 

 3. During the night of October 7 (above 

 Blackwater River) a little snow fell, 

 but it disappeared during the following 

 day. On the night of October 12 (above 

 Fort Wrigley) 4 in. of snow fell, and on 

 the night of October 14 another fall of 

 snow occurred. Some ice was seen 

 drifting on the west side of the Mac- 

 kenzie on October 15 (above mouth 

 Nahanni River). ^ On the following day 

 the drifting ice had greatly increased in 

 quantity, and on October 17 our progress 

 by canoe was arrested. At this time 

 the last of the tree sparrows and a few 

 other hardy species left for the South. 



Fort Simpson: The Liard was par- 

 tially closed at its mouth on October 

 21, but broke away once or twice before 

 it finally set fast. The weather from 

 October 21 to 25 was considerably milder 

 than it had been during the previous 



' It should be noted that the appearance of 

 drifting ice at this early date was almost unprece- 

 dented. 



