46 NORTH AMERICAN FAUNA. [no. 27. 



outlet until very late in the autumn, or throughout the winter. At 

 the rapid of Bear River the ice forms from the bottom and sides and 

 finally completely blocks the stream. The resulting overflow con- 

 tinually adds to the volume of ice, which reaches an enormous thick- 

 ness. The heat of an ordinary summer is insufficient to melt this 

 mass entirely, and great quantities of it usually persist on the south 

 or sheltered bank throughout the season. This vast accumulation of 

 ice probably prevents the lower part of the river from opening as 

 soon as the early disruption of its upper part would seem to justify. 

 Richardson states that the louver part usually opens in June, while 

 Petitot gives the usual time as the last of May. In 1004 it was al- 

 ready open when the Mackenzie broke up at Fort Norman on May 21. 



THE BARREN GROUNDS. 



Under this heading will be considered the great area lying to the 

 northward and northeastward of Great Bear and Great Slave lakes. 

 It is watered by the Anderson. Coppermine, Great Fish, Thelon or 

 Ark-i-linik, and many smaller rivers. With the exception of Great 

 Fish River all those named are wooded to some extent on their upper 

 portions, but by far the greater part of the area drained by them 

 is treeless. It may be well to trace the northern boundary of the. 

 great transcontinental forest from the western shore of Hudson Bay 

 to the mouth of the Mackenzie. 



Starting from the mouth of Churchill River, Hudson Bay, the tree 

 line follows the shore closely for a few miles and then curves gently 

 inland (see PI. II). Thence it extends northwesterly, cross- 

 ing Nueltin, or Island Lake; Ennadai Lake on Kazan River: and 

 Boyd Lake on the Dubawnt. Just north of 60° on Artillery Lake 

 is the next point where we have a definite dividing line. Between 

 the Dubawnt and Artillery Lake is the valley of the upper Thelon, 

 or Ark-i-linik, along whose banks the forest extends in a narrow line 

 far into the general treeless area. This northward extending tongue 

 of forest will be more fully described beyond. 



From Artillery Lake the line extends northwestward to Point 

 Lake, curving toward the southwest in the interval and crossing Lake 

 Mackay south of latitude 64°. From Point Lake, whose shores are 

 practically devoid of trees, nearly to latitude 07°, the banks of the 

 Coppermine are so thinly wooded that the river may be taken as 

 the approximate boundary of the woods. Spruces occur on the Cop- 

 permine as far north as the mouth of Kendall River, but are absent 

 from the summit of the divide between there and Great Bear Lake 

 and reappear on lower Dease River. Between Dease River and the 



