Central Part of British North America. 233 
towards the south merges into open prairie, the clumps of 
copse and young poplars are found only nestling on northern 
exposures. The last outliers of the woods to the south form 
“islands,” as they are called in the country, which make 
a great show from a distance, but when approached, are 
found by the disappointed traveller to consist merely of a 
small species of willow, that will yield neither firewood nor 
shelter. 
- The true arid district, which occupies most of the country 
along the South Saskatchewan, and reaches as far north as 
Lat. 52°, acquires even very early in the season a dry parched 
look. Inthe northern district, the accumulation of humus 
- and the distribution of the pleistocene deposits have given rise 
to a great variety in the nature of the soil; but to the south, 
the cretaceous and tertiary strata almost everywhere form 
the surface, so that the stiff clay soil, which is often highly 
impregnated with sulphates of soda and lime, bakes under the 
heat of the sun into a hard and cracked surface. This must 
be the principal reason for the arid plains ranging to such a 
high latitude, as there is quite a sufficient quantity of mois- 
ture in the atmosphere during the summer months to support 
a more vigorous vegetation. This is seen to be the case even 
as far south as Lat. 49° 30’ N., where, at the Cyprés Hills, and 
also on the south sides of the deep valleys and other exposures 
sheltered from the sun’s rays in early spring, pines, spruce- 
firs, poplars, and many varieties of the northern type of 
vegetation, appear under congenial but strictly local con- 
ditions. In the arid country the characteristic plants are the 
prickly prairie apples (Opuntia), and the shrub-sage or 
absinthe (Artemisia) ; and in the trough-like valleys that lie 
east and west far out in the bare plains, these plants may 
sometimes be seen in full possession of the sunny slopes on 
the north side, while the opposite side of the valley is clothed 
with green and arborescent vegetation ; while at the same time, 
showing that it is not local springs that cause the difference, 
the stream itself is often dried up into a chain of muddy 
pools. The arid district, although there are many fertile spots 
throughout its extent, can never be of much advantage to us 
