The favorite method of explaining these conditions has slightly changed within recent years, as already remarked. For whereas the classic example at Glarus was at first spoken of as a double fold-in from both sides toward the Sernf Valley, this is now universally spoken of as a "thrust fault," with the rocks all pushed one way. Incidentally it may be noted that this very fact that what was long regarded as two completely overturned folds is now spoken of as one flat-lying thrust fault, is _prima facie_ evidence that there is here _no physical proof_ of any real overturning of the strata, such as we do find on a very small scale in true folded rocks. The latter can usually be measured in yards, feet, or inches; while in this example at Glarus the area involved would be measured in many miles, and in some very similar examples to be presently mentioned from America the measurement could best be made in degrees of latitude and longitude or in arcs of the earth's circumference. In these larger examples it is manifestly impossible that there should be any physical evidence sufficient to indicate a huge earth movement of this character, especially when, as is usually the case, both the upper and the lower strata are _quite uninjured in appearance_. No; the fossils are here in the wrong order, that is all. And so, to save the long established doctrines of a very definite order of successive life-forms, this theory of a "thrust fault" is offered as the best available explanation. As Dr. Albert Heim himself once expressed it very naively in a letter to the present writer, that the strata over these large areas are in a position manifestly at direct disagreement with the received order of the fossils, "is a fact which can be clearly seen,--only we know not yet how to explain it in a mechanical way." An example in the Highlands of Scotland was about the next to be discovered. Here, as Dana says, "a mass of the oldest crystalline rocks, many miles in length from north to south, was thrust at least ten miles westward over younger rocks, part of the latter fossiliferous;" and he further declares, "the thrust planes _look like planes of bedding, and were long so considered._"[42] Sir Archibald Geikie and others had at first described these beds as naturally conformable; and when at length they were convinced that the fossils would not permit this explanation, Geikie gives us some very picturesque details as to how natural they look. The thrust planes, he says, are with much difficulty distinguished "from ordinary stratification planes, like which they have been plicated, faulted, and denuded. Here and there, as a result of denudation, a portion of one of them appears capping a hilltop. One almost refuses to believe that the little outlier on the summit does not lie normally on the rocks below it, but on a nearly horizontal fault by which it has been moved into its place." Of a similar example in Ross Shire he declares: