anticlines having in each case been removed.

Take again the section of the Diablerets (Fig. 47), in which the Tertiary strata are doubled back upon themselves

FIG. 48.

SECTION ACROSS DENT DE MORCLES (Renevier).

1, Schistose rocks, etc.; 2, Carboniferous strata; 3. Jurassic strata; 4, Cretaceous strata ; 5. Tertiary strata;, S, S, Cretaceous and Tertiary rocks inverted; 7, thrust-plane.

A similar,

in a series of sharp overturned flexures. but somewhat more complicated, structure appears in the Dent de Morcles (Fig. 48), where the remarkable

FIG. 49.

INVERSION AND OVERTHRUST IN THE MOUNTAINS SOUTH OF THE
LAKE OF WALLENSTADT (E. Fraas, after A. Heim).

s, Schistose rocks; p, Permian; wj, bj, Jurassic; c, Cretaceous; e, Eocene. The Permian strata (p) are turned upside-down and thrust upward over the contorted Eocene (e).

overturn flexure rests upon a thrust-plane. Here, again, the strata, it will be observed, are doubled back upon themselves, or turned upside-down. Obviously these mountains are monuments of excessive erosion.

Similar evidence of vast rock-removal is furnished by the remarkable double-folds and overthrusts in the mountains of the Cantons Glarus and St. Gall, as described by Heim and others (See Fig. 49.)

Similar conclusions may be drawn from the appearances presented by every kind of rock-structure throughout the whole extent of the Alps.

In the Jura mountains the rock-foldings are sometimes symmetrical, and anticlines and synclines now and again coincide with hills and valleys respectively, as in Fig. 50.

It will be observed, however, that the synclinal strata have suffered less erosion than the intervening

FIG. 50. SYMMETRICAL FLEXURES OF THE JURA MOUNTAINS.
Anticlinal mountains and synclinal valleys.

anticlinal strata. In the western part of the same range of mountains the folds are less symmetrical, but they yield the same evidence of denudation. The accompanying section (Fig. 51, p. 116) shows, indeed, that the saddlebacks have not only been considerably reduced, but are even beginning to develop into valleys; while the synclines, on the other hand, have experienced less erosion, those with approximately vertical axes appearing as dominant heights.

Excellent examples of the same phenomena are furnished by the Carpathians—a mountain-chain also

of relatively recent age. Fig. 52 (p. 116) exhibits the structure of a part of the chain in which the folds are unsymmetrical. Here it will be observed that the tops of the anticlines have in every case been greatly reduced; but the synclines, owing to the isoclinal arrangements of the strata, do not tend to develop into hills. In point of fact, unsymmetrically folded strata behave very much. in the same way as beds having a persistent dip in one direction. When the anticlines have been truncated the strata appear at the surface as a series of isoclinal beds, some of which are relatively more resistant than others. In time, therefore, these harder beds crop out as well-marked ridges or escarpments, according as the angle of dip is high or relatively low. But no sooner do the axes of the folds approach the vertical, and the flexures become symmetrical, than the superior strength of the synclinal structure at once asserts itself. This is well

SECTION ACROSS PART OF THE MIDDLE CARPATHIANS (Vacek).

Symmetrical synclines forming mountains. This section crosses another portion of the Sandston Zone shown in Fig. 52. FIG. 53.

illustrated by Fig. 53, where we have a series of syn

FIG. 54. SECTION ACROSS THE APPALACHIAN RIDGES OF PENNSYLVANIA. (H. D. Rogers.)

anticlinal hollows.

Synclinal mountains and

clinal troughs forming conspicuous mountains, while the intermediate anticlines correspond for the most part with valleys and depressions.

If it be true, therefore, that the denudation of young mountains, such as the Alps and the Carpathians, has been guided and determined to a large extent by geological structure, we ought to meet with still stronger evidence of a like kind in mountain-ranges of greater antiquity. The mountain-systems we have been considering are of Cenozoic age; they are among the latest great upheavals of the world. We see in the Appalachian Chain of North America a very much older system, for it came into existence about the close of Paleozoic times. Being of such enormous antiquity, the Appalachians ought to give evidence of correspondingly great denudation. All the weak geological structures should have collapsed and disappeared ages ago; the heights ought not to coincide with anticlines. The accompanying section across a portion of the chain in Pennsylvania shows that this has actually happened, symmetrical synclines having as usual developed into hills, while anticlines have been degraded.

Similar evidence might be adduced from