Hudson. Bay. — Mackenzie District. 357 
the specimens of spruce and larch become much dwarfed, twisted and wind 
swept, but this condition is reached farther south in extiosed locations along 
the shores of the numerous lakes that such plants as Salir Phlebophylla = 
anglorum cling to the rocks and Vaccinium uliginosum, as well, as Fumiperus 
Sabina var. procumbens assume a typical dwarf habit. The islands in Great 
Slave Lake are wind swept and their vegetation becomes stunted and dwarf, 
so as to remind one of that existing at the northern tree limit. 
Forests exist, on the mountains which parallel the western bank of the 
Mackenzie River, where it joins the Nahanni River in latitude 62° ı5’ N, 
Here at the apex of the confluence rises a mountain 2,500 feet (760 m). Its 
northern face is steep and terraced. The slopes are as well wooded as the 
nature of the soil will allow, the common trees ascending together with Salir 
alaxensis and lu, to 2,000 feet, and occuring at their upper limit as 
EE shrubs 
The eme summit of the Nahanni Mountains is tenanted by Salix myrtillifolia, S. alaxensis, 
Dryas an D. Drummondii, Pedicularis euphrasioides, Pinguieula vulgaris, Anemone 
Richardsoni. 
spen Forest. Lying between the coniferous forest proper and the prairie 
is a belt of aspen, Populus tremuloides, which extends from the international 
boundary in latitude 49° all around the prairie region in the north. It pene- 
trates the prairie region, and northward it enters the coniferous forest, where- 
ever there is good dry soil, and is the bulk of the forest in the Peace River 
country and on the plains Iying along the Liard and the Mackenzie rivers. 
It keeps out of the flood plains of the river valleys in its northwestern home 
and never appears on islands or on alluvium at any time. 
The balsam poplar on the other hand makes its home on the river 
bottoms and islands and is seldom found anywhere else. (Populus bal- 
samifera-Facies.) It grows to immense size on the Peace, Athabasca, 
Liard, Slave and Mackenzie rivers, where it is not uncommon to see trees 
over six feet in diameter. It is this species and the white spruce that are 
found as driftwood on the shores of the Arctic Sea, as Picea alba and Populus 
balsamifera constitute the trees of the islands and flood plains of the Mackenzie 
and its tributaries, which are constantly changing and being re-formed by the 
spring freshets. Spruce grows on the larger islands, especially at the upper 
end before erosion takes Blick crowding out the old poplars, for spruce trees 
are never found on a new island where poplars abound in all stages from 
trees four feet in diameter to seedlings growing in the mud recently E B: 
at the I sn of ie islands. 
a 3 natans, P. praelongus, P. perfoliatus, 
an edeing to the stream associated with Carex utrieulata, C. aqua ee 
Bi Acorus calamus, Caltha natans, Petasites (Nardosmia) sagittata, Sparganium simplex 
eurycarpum. 
Tycarp 
Lake Formation. The islands in the northern arm of Great Slave Lak . 
show many lakelets and swamps in which, as well, as ae the low shor 
