A still more astonishing thing from the standpoint of the current theories is that these conformable relations of incongruous strata are often _repeated over and over again in the same vertical section_, the same kind of bed reappearing alternately with others of an entirely different "age," that is, appearing "as if _regularly interbedded"_ (A. Geikie) with them, in a manifestly undisturbed series of strata. Here again we have a very formidable series of facts whose gravamen is directed wholly against the artificial distinctions in age between the different groups of fossils; and their argument is an eloquent plea that the fossils are neither older nor younger but all of a similar age. 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."[41] [Footnote 41: "Der Bau der Schweizeralpen," p. 17.]