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 Palaeozoic mountains,
_with four Cretaceous valleys in between_, one of these valleys, the
Crow's Nest Trough, being ninety-five miles long.
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