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NATURALIST'S GUIDE TO THE AMERICAS 



large numbers of musk oxen inhabited 

 the northern and eastern part of this 

 area, but few, if any, of this notable 

 species now remain. Large numbers 

 of a few species of geese and ducks breed 

 within this area, but it does not abound 

 in large marshy tracts which form the 

 favorite nesting places of waterfowl. 



E. The Mackenzie Valley proper. The 

 Mackenzie (taken in a restricted sense 

 as comprehending only that part of the 

 river known under this name) has a 

 course of over 900 mi. from Great Slave 

 Lake to the Arctic Sea. It averages 

 over a mile in width and is usually deep, 

 with a current of from 2 to 6 mi. an hour. 

 Its general course is to the northwest. 

 It is bordered mainly by sandy or grav- 

 elly beaches and occupies a narrow, com- 

 paratively shallow valley, through which 

 it flows in a succession of gentle curves. 

 Many low islands, usually well wooded, 

 occur throughout its course. Its rocks 

 are chiefly Devonian. 



Issuing from Great Slave Lake, the 

 Mackenzie first follows a general west- 

 erly course for nearly 300 mi. The tribu- 

 taries which it receives in this stretch, 

 with the exception of the Liard, are of 

 minor importance; The Horn Moun- 

 tains, a long low ridge lie at some dis- 

 tance north of the middle of the stretch. 

 To the southward occur other lower 

 ranges, the principal one being Trout 

 Mountain. These mountains are very 

 imperfectly known, but they are too low 

 to support a fauna and flora differing 

 appreciably from that of the surrounding 

 country. A large part of the country 

 bordering this part of the Mackenzie is 

 swampy, and it is all well wooded. 

 Nearly all the species of trees of the 

 great subarctic forest are represented. 



A short distance north of latitude 62° 

 the Mackenzie strikes a spur of the 

 Rocky Mountain system, the Nahanni 

 Mountains, is deflected toward the 

 north, and for some distance flows close 

 to their bases. At the point where the 

 Mackenzie first approaches them the 

 nearest peaks are from 200 to 2500 ft. 

 in height and are sparsely wooded to 

 their summits. Farther back they rise 



much higher, and above an altitude of 

 2500 ft. are treeless. In early summer 

 these mountains are capped with snow, 

 but this disappears entirely beneath the 

 almost continuous sunlight of mid- 

 summer. 



Near this point the fauna receives an 

 infusion of Rocky Mountain types. 

 Among mammals, these include a chip- 

 munk (Eutamias borealis caniceps) com- 

 mon in northern British Columbia and 

 southern Yukon. The Rocky Mountain 

 shrew (Sorex obscurus) also occurs, but 

 has reached also the middle Athabaska 

 and Great Slave Lake, farther south. 

 The white mountain sheep (Ovis dalli) 

 occurs in the Nahanni Mountains at 

 some distance back from the river and 

 also farther north, but is not found near 

 the Mackenzie. Among birds the blue 

 grouse {Dendragapus obscurus), and the 

 Townsend solitaire {Myadesles town- 

 sendi) seem to reach their northeastern 

 limit on the mountains near the mouth 

 of the North Nahanni. The northern 

 varied thrush (Ixoreus naeviusmeruloides) 

 also reaches the Mackenzie near this 

 point, and follows its valley to the delta. 



Continuing northward, the Mackenzie 

 is bordered on the west by a broad ex- 

 panse of mountain country, mainly un- 

 explored. A few low spurs of the same 

 system cross the river and appear in 

 the form of isolated peaks or discon- 

 nected ranges to the eastward of its 

 valley. The principal western tribu- 

 taries between latitude 62° and 65° are 

 the Red Rock and Gravel rivers. In the 

 same interval the Mackenzie received 

 several small streams which drain the 

 country east of the river. One of the 

 largest of these is the Blackwater 

 Mount Clark, which is visible from the 

 river at some distance below the mouth 

 of this stream, has an estimated altitude 

 of 3500 ft., and is the highest of the 

 mountains east of the Mackenzie. The 

 most conspicuous landmark in the im- 

 mediate valley is Roche Trempe-l'eau, 

 a limestone mass which rises abruptly 

 from the water's edge a short distance 

 north of latitude 63°. Bear River, 

 the principal eastern tributary of the 



