The Rocky Mountains furnish examples of many kinds of natural phenomena on the very largest scale, and those of the sort here under consideration are no exception to this rule. For here we have an immense area east of the main divide, extending from the middle of Montana up to the Yellowhead Pass in Alberta, or over 350 miles long, where the tops of the mountains consist of jointed limestones or argillites of Algonkian or pre-Cambrian "age," resting on soft Cretaceous shales. Often the greater part of the mass of a range will consist of these "older" and harder rocks, which by the erosion of the soft underlying shales are left standing in picturesque, rectangular, cathedral-like masses, easily recognizable as far off as they can be seen. And the almost entire absence of trees or other vegetation helps one to trace out the relationship of these formations over immense areas with little or no difficulty. In the latitude of the Bow River, near the Canadian Pacific main line, there is a long narrow valley of these Cretaceous beds some sixty-five miles long, called the Cascade Trough, with of course pre-Cambrian mountains on each side. Somewhat further south there are two of these Cretaceous valleys parallel to one another, and in some places _three_; while just south of the fiftieth parallel of latitude, at Gould's Dome, there are actually _five parallel ranges_ of these Palæozoic mountains, _with four Cretaceous valleys in between_, one of these valleys, the Crow's Nest Trough, being ninety-five miles long. But we ought to take a nearer view of these wonderful conditions. A convenient point of approach will be just east of Banff, Alberta, near Kananaskis Station, where the Fairholme Mountain has been described by R.G. McConnell of the Canadian Survey. The latter remarks with amazement on the perfectly natural appearance of these Algonkian limestones resting in seeming conformability on Cretaceous shales, and says that the line of separation between them, called in the theory the "thrust plane," resembles in all respects an ordinary stratification plane. I quote his language: "The angle of inclination of its plane to the horizon is _very low_, and in consequence of this its outcrop follows a very sinuous line along the base of the mountains, and _acts exactly like the line of contact of two nearly horizontal formations_. "The best places for examining this fault are at the gaps of the Bow and of the south fork of Ghost River.... The fault plane here is nearly horizontal, and the two formations, viewed from the valley, _appear to succeed one another conformably."[48] [Footnote 48: Annual Report, 1886, Part D, pp. 33, 34.] This author adds the further interesting detail that the underlying Cretaceous shales are "very soft," and "have suffered very little by the sliding of the limestone over them."[49]