5. Our last fact demands a somewhat more extended consideration; but it
may be stated in advance briefly as follows:
In very numerous cases and over hundreds and even thousands of square
miles, the conformable conditions specified in the previous fact are
exactly reproduced _upside down_; that is, very "old" rocks occur with
just as much appearance of natural conformability on top of very "young"
rocks, the area in some instances covering many hundreds of square
miles, and in one particular instance in Montana and Alberta covering
about five or six thousand square miles of area.
The first notable example of this phenomenon was discovered at Glarus,
Switzerland, a good many years ago; since which time this locality has
become a classic in geological literature, and has called out many
ponderous monographs in German and French by such men as Heim, Schardt,
Lugeon, Rothpletz, and Bertrand. This example, which was first (1870)
called the Glarner Double Fold by Escher and Heim, is now universally
called a nearly flat-lying "thrust fault," in accordance with the
explanations since adopted of similar phenomena elsewhere. Without
obtruding unnecessary technicalities upon my non-professional readers, I
may quote the words of Albert Heim as to the conditions as now
recognized in these parts:
"These flat-lying faults, of which those at Glarus were the first to be
discovered, _are a universal_ _phenomenon_ in the Northern and Central
Alps.
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