mountains owe most of their present elevation—took place at a relatively late geological period. Many of the folded and fractured rocks, indeed, are of no greater antiquity than the soft clays and sands over which London is built. And yet, although the chain belongs to so late a date, its rocks everywhere bear witness to great erosion. Enormous masses of material have been gradually removed, and the original surface, due to folding and displacement, has been more or less profoundly modified.

The sketch-section across the Swiss Alps (Fig. 40, p. 110) gives the general arrangement of the strata,. and enables us in some faint measure to appreciate the degree of denudation which has already been experienced by these relatively young mountains. Grant, if you will, that the folding of the strata may have resulted in a kind of chaos at the surface-that the ground along the axes of anticlinal arches may have been ruptured, and the rocks everywhere tumbled in confusion-yet we have still to account for the wholesale removal of the abundant débris-the shattered reefs and dislodged mountain-masses. We cannot, in short, escape from the conclusion that an enormous amount of denudation has taken place. So profoundly has the original configuration been modified, that it is only when the mountains are viewed in the broadest way that any coincidence between underground structure and surface-features can be observed. Even where anticlines still form hills and mountains it is obvious that they have yet

suffered extensive degradation. (See Fig. 41.) Not infrequently, indeed, they are more or less deeply

Anticlinal mountain.

trenched-valleys running along their axes, an appearance well shown in Fig. 42. Synclinal hollows

Schortenkopf

FIG. 42.

SECTION ACROSS THE SCHORTENKOPF, BAVARIAN ALPS

(E. Fraas).

Anticlinal valley in calcareous rocks and shales (Triassic.)

now and again coincide with depressions at the surface, as in Fig. 43; but they just as often, or even

Hinter Kaiser

Kaiser Thal

Vorder Kaiser

FIG. 43. SECTION ACROSS THE KAISERGEBIRGE, EASTERN ALPS (E. Fraas). Synclinal valley in calcareous rocks and shales (Triassic).

Sickie-shaped overfold.

more frequently, form elevations, as in Figs. 44, 45. In every case, however, the evidence of denudation

FIG. 46. SECTION ACROSS THE NORTHERN LIMESTONE ALPS (E. Fraas). 1, Crystalline schists; 2, Permian; 3, Bunter; 4, Muschelkalk; 5, Limestone (Wettersteinkalk); 6, Dolomite; 7, Jurassic and Cretaceous.

is conspicuous. Nor is this less clearly seen in the more complicated structures of the Alps. In the fol

Pointe de la Houille

FIG. 47. SECTION ACROSS THE DIABLERETS (Renevier).
Tertiary strata showing a succession of overfolds.

lowing section, for example (Fig. 46), we have a series of various calcareous strata and underlying schists compressed into folds and dislocated, the tops of the