Page:Canadian Alpine Journal I, 2.djvu/62

228 all the debris, the rocks and pebbles, the sand and the clay, delivered to them by the agents working at higher levels. The main valleys have generally been cut right across the direction of the great ranges, as shown by the Bow, the Saskatchewan and the Brazeau on the east, and the Kicking Horse on the west.

Were the rivers there before the mountains, and did they carve their valleys downwards as fast as the upheaving forces pushed the mountains aloft; or did great lines of faulting provide channels that the rivers merely had to deepen? I am inclined to think that the main rivers at least were earlier than the mountain ranges and simply held their ground during the ages of uplift.

Passing through the Rockies by the lower valleys as in the Kicking Horse Pass, one sees mainly the work of running water. Where the river has a somewhat gentle slope, like the Bow, the valley which it has cut is broad and open, with terraces on each side sweeping with a curve up to the foot of the cliffs, which have their bases buried under vast heaps of talus blocks from above, mainly quarried by frost. The broad valleys seem peaceful enough, and it is hard to imagine the relentless war of the river and its tributary torrents upon the mountains until one works out the cross-section which they have cut from the summits on one side to those on the other, and figures the many cubic miles of rock which have been destroyed and carried down to the plains by the flow of water.

Where the slopes are steeper we have turbulent rivers, like the Kicking Horse, rapidly cutting down their V-shaped valleys into canyons, and our sense of the endless strife grows more vivid as we watch them leaping down thousands of feet in a few miles, dragging with them the rocks which have rolled from the sides and using them as powerful tools to cut the canyon still deeper.