a reported length of 375 miles,[44] while in another instance the upper
strata are said to have been pushed about eleven miles in the direction
of the "thrust."[45] These conditions, we are told, "have provoked the
wonder of the most experienced geologists,"[46] because of the perfectly
natural appearance of the surfaces of the strata affected; or as this
same writer puts it, "The mechanical effort is great beyond
comprehension, but the effect upon the rocks is inappreciable," and "the
fault dip is often parallel to the bedding of the one or the other
series of strata."[47] Which means, in other words, that these "thrust
planes" _look just like ordinary planes of bedding between conformable
strata_.

[Footnote 44: Bailey Willis, Geol. Survey, Report, Vol. 13, p. 228.]

[Footnote 45: C.W. Hayes, _Bull. Geol. Soc_., Vol. 2, pp. 141-154.]

[Footnote 46: Willis, _op. cit_., p. 228.]

[Footnote 47: Willis, _op. cit_., p. 227.]

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