1908.] PHYSICAL GEOGRAPHY GREAT SLAVE LAKE. 27 



trating the crystalline schists, while two others stretched north and south 

 along the junction of these with the newer sedimentaries, and the fourth ex- 

 tended over the flat-lying Devonian to the west. The southern arm; as stated 

 before, has been silted up hy Slave River. 



The eastern or archa?an portion of the lake has an irregular outline, and is 

 dotted with rocky islands. It is reported to be much deeper than the western 

 part, and its water is exceedingly clear and limpid. 



* * * The northern arm is situated nearly opposite the mouth of Slave 

 River, and is narrow and filled with islands. At its upper end it contracts, and 

 opens out again under the name of hake Brochet, which communicates in turn 

 by a short river with Marten Lake. Yellow Knife River, at the mouth of which 

 old Fort Providence was situated, and which franklin ascended on his way to 

 the Coppermine, enters tins arm from the east. 



The [western] arm of Great Slave hake rests on the flat-lying Devonian 

 limestones, and is wider, and presents a greater expanse of water, unbroken by 

 islands, than either of the other divisions. Its southern shore has a gently 

 sinuous outline, ami is characterized by low banks and gently shelving beaches, 

 which are often thickly strewn with boulders. The banks : s pointed out by 

 Richardson are often built up of drift timber. The northern shore is more 

 uneven, and is indented by several deep bays. The water of Great Slave hake 

 between Slave River and the .Mackenzie, is never entirely clear, as a portion of 

 the sediment brought down by the former stream is held in suspension and 

 drifts slowly eastward for a hundred miles. The impurity of the water is 

 especially noticeable along the southern shore, and the shallowness of this part 

 of the lake is undoubtedly caused by the partial settlement of the suspended 

 material." 



Great Slave Lake lies wholly within the forested region, though 

 some of its eastern affluents drain large areas of treeless country. 

 Its southwestern shores, being watered by rivers coining from the 

 south and southwest, are well wooded, while the northern shores. 

 exposed for most of the year to cold winds from the north and watered 

 by colder streams, are poorly wooded. The soil conditions, also, being 

 more favorable on the southern side of the lake, exert a marked influ- 

 ence on the foresting. 



The Eastern Arm of the lake, however, is largely removed from 

 these modifying influences, and the conditions on its northern and 

 southern borders are more nearly uniform. Several streams, whose 

 courses and drainage are practically unknown, enter this arm on the 

 southern side. Hoarfrost River, draining Walmsley Lake, and Lock- 

 hart River, carrying the waters of Mackay, Aylmer. Clinton-Colden, 

 and Artillery lakes, which lie almost wholly in the Barren Grounds, 

 fall into this arm near its eastern extremity. The country bordering 

 its northern shore is rocky and sparsely wooded, and contains a great 

 many lakes, but the streams flowing thence into Great Slave Lake are 

 tew in number and comparatively insignificant. 



The Northern Arm of Great Slave Lake, as before stated, lies along 

 the junction of the primitive and the newer formations. Its eastern 

 shore, therefore, is mainly composed of granite, while its western 



"Ann. Kept. Can. (ieol. Surv.. IV, p. 65 1» et seq., Is'.H. 



