Page:Canadian Alpine Journal I, 2.djvu/58

226 contrasted with the complex foldings and faultings in different directions shown by the Alps. The folds in our mountains are often rather broad and uncomplicated, especially toward the Pacific side of the range; while toward the northeast vast blocks of the sediments. 25 to 40 miles long, from nothwestnorthwest [sic] to southeast, several miles wide and sometimes more than 15,000 feet thick, seem to have been split off from the earth's crust, the southwest side being tipped down, and the northeast side slid up over the next block toward the prairies, the last block riding seven miles out over the region of the foothills before the thrust from behind ceased. Mr. McConnell, of the Geological Survey, whose work I am following here, estimated that along Bow Pass this over-riding or telescoping of range after range sums up to a shrinkage of 25 miles. If the blocks were set back in their place again and the strata ironed out flat Golden would be 25 miles farther from Calgary than now.

The blocks which build the eastern ranges have various tilts. In the Brazeau Valley I found the inclinations run from 28° to about 50°, blocks with the lower dip presenting a steep cliff of 3,000 or 4,000 feet toward the northeast, and a gentler slope following the surface of the strata, toward the southwest. These rather gently tilted blocks provide the "writing-desk" type of mountain so common in the eastern Rockies, e.g., near Banff, rather scorned by certain English mountain climbers. The steeper blocks, with a dip of 50° or more, make very rugged, striking mountains, however, often with two or three more resistant layers of quartzite standing out as sharp ridges, while the softer slates have been carved away by the weather.

The great faults that separate block from block sometimes run out into sharp folds at one end, as in Sentinel Mountain, near the Kootenay Plains on the Saskatchewan.