river channels may be traced from afar across the prairie by the
winding band of trees growing beside the water. The treeless part of the
plains, the prairie proper, has a triangular shape with an area twice as
large as that of Great Britain. North of the Saskatchewan river groves
or "bluffs" of trees begin, and somewhat farther north the plains are
generally wooded, because of the slightly more humid climate. It has
been proved, however, that certain kinds of trees if protected will grow
also on the prairie, as may be seen around many of the older
farm-steads. In the central southern regions the climate is arid enough
to permit of "alkaline" ponds and lakes, which may completely dry up in
summer, and where a supply of drinking-water is often hard to obtain,
though the land itself is fertile.

_The Cordilleran Belt._--The Rocky Mountain region as a whole, best
named the Cordillera or Cordilleran belt, includes several parallel
ranges of mountains of different structures and ages, the eastern one
constituting the Rocky Mountains proper. This band of mountains 400 m.
wide covers towards the south almost all of British Columbia and a strip
of Alberta east of the watershed, and towards the north forms the whole
of the Yukon Territory. While it is throughout essentially a mountainous
country, very complicated in its orographic features and interlocking
river systems, two principal mountain axes form its ruling features--the
Rocky Mountains proper, above referred to, and the Coast Ranges. Between
them are many other ranges shorter and less regular in trend, such as
the Selkirk Mountains, the Gold Ranges and the Caribou Mountains. There
is also in the southern inland region an interior plateau, once probably
a peneplain, but now elevated and greatly dissected by river valleys,
which extends north-westward for 500 m. with a width of about 100 m. and
affords the largest areas of arable and pasture land in British
Columbia. Similar wide tracts of less broken country occur, after a
mountainous interruption, in northern British Columbia and to some
extent in the Yukon Territory, where wide valleys and rolling hills
alternate with short mountain ranges of no great altitude. The Pacific
border of the coast range of British Columbia is ragged with fjords and
channels, where large steamers may go 50 or 100 m. inland between
mountainous walls as on the coast of Norway; and there is also a
bordering mountain system partly submerged formin