Central Part of British North America. 231 
live wholly by the chase of the buffalo, and prefer, in con- 
sequence, to pitch their tents along the edge of the woods, for 
the sake of shelter, and at the same time to be near their game. 
Either by accident, or for the purpose of making signals, the 
prairies round their camps are generally burnt every few 
years, and, as a rule, where coniferous trees are destroyed, 
they are never replaced by the same stock; but the rich 
alkaline soil is at once seized upon by the wafted seeds of the 
aspen poplar, to the exclusion of other trees. 
It is true that similar fires take place in the thick wood 
country and in the forests of the Rocky Mountains; but al- 
though they do much damage, the chance of their recurring 
on the same spot within a short enough time completely to 
remove the timber is small. Where the poplar seeds cannot 
reach such burnt spots, they are usually crowded with the 
gaudy plants of Hpilobium angustifolium, among which the 
young pine seedlings can gain a footing, so that the forest 
often reverts in such a case to the coniferous type; but the 
thickets which spring up, strangely enough, very seldom con- 
tain plants of Abies alba, but almost invariably consist of 
the Pine which I have alluded to as allied to P. inops. 
The Saskatchewan and other rivers of the prairies flow 
through valleys rarely a mile in width, and excavated to the 
depth of 200 to 300 feet below the general level. The river 
winds from side to side of this valley, successively rounding 
rich alluvial flats, which sustain a rich and very different kind 
of vegetation from that of the plains above. In such low 
situations, stragglers from the eastern flora are found to ex- 
tend far beyond the western limit of where they continue to 
grow on the general surface of the country. Thus the false 
sugar maple (Negundo frawinifolium) may be found as far 
-west as Long. 108° in the valley of the North Saskatche- 
wan; and on an island in the same river, a short distance 
above Fort Carlton, the red elm (Ulmus fulva) was observed. 
The oak follows up the valley of the Assineboine River as far 
west as Long. 100°. The true sugar-maple does not pass 
beyond the Red River, in which longitude is also found the west- 
ern limit of the wild plum (Prunus americana), beech, iron- 
wood, ash, cedar, arbor-vite, Weymouth pine, and other more 
