4. The ring-shaped system is in direct contrast with the last. It is found where mountain chains are arranged in a circle, inclosing a plateau of larger or smaller extent. There are two marked examples of this form in Europe: Bohemia and Transylvania. The ring of mountains around the former is made up of a number of ranges, which dovetail together at the ends, making a unit, but only a rude circle, speaking with mathematical exactness. The inclosed basin is only relatively a lowland; it is rigid with hills and low mountains, yet of such little importance, in comparison with the rim of peaks, that the common name, the “Bohemian Kettle,” has begun to have an accredited significance, and is stronger than the more loosely-used word Basin. Transylvania, too, partakes of similar characteristics. Its border consists of a number of minor ranges, of varying heights, up to 1800 feet; and the central hollow, which is much more strongly marked by hilly land than Bohemia, lies 2200 feet above the Adriatic. The ring-shaped system is one of the rarest met of all. They are, however, observed in abundance on the moon.
5. Just as rare is the form where ranges intersect in the form of a cross, those running, for example, from north to south, meeting those running east and west. As an instance of this, Humboldt cites the confluence of the Himalaya, the Kuenlun, the Hindoo Koosh, and the Belor or Belurtagh Mountains. The belt between 35° and 40° N. lat. is remarkable for its gridiron-shaped mountain system, the points of conjunction being marked by knots of peaks of colossal height. The most remarkable one of these is the lofty Pamir Pass, between 37° 30′ and 40° 5′ N. lat., and 18,000 feet high, known, historically, from the sixth century, and described by Marco Polo, as well as by the ancient Greek historians. The Persians dwelling in the neighborhood term it the Roof of the World. Elsewhere the same feature is observable, though on a scale of less magnitude. So in the Altai range at Lake Yetzkoi, in the western Swiss Alps, and in the porphyritic chain of Room-Elee, known to the ancients as Rhodope, and now as the Despoto Dagh. This gridiron-shape of some mountain systems seems to be the result of upheavals at different times, which necessarily occasions the most broken configuration at the point where a chain of more recent formation has been projected through one of older date.
The varying relations of length, breadth, direction, connection, and severance of mountain ranges give great diversity to them, and impart to every system a character of its own. To the features just indicated must be added vertical or precipitous descents, for the influences which they exert upon the possibility of man’s constructing mountain roads, are very great. The extent of these sudden depressions, or, more exactly, the relation which the distance from the base to the pass bears to the distance from the base to the summit, gives a key to the uses of certain mountains as adjuncts of civilization, and shows how some ranges rather than others may become the abode of men, and produce marked effects on human culture and the world’s history.
I have before alluded to the comb-like structure of most mountain chains. The resemblance is more striking than may appear; for not only do the peaks correspond in general uniformity of height with the teeth of the comb, but the equally uniform height of the passes from the base corresponds with the uniform thickness of the solid part of the comb. The relation, however, of the distance from the base to the passes, to the distance from the base to the peaks, is widely various. Humboldt has estimated it in a few leading chains as follows:—
| Himalayas. | |||
|---|---|---|---|
| Height of chain, | 25,000 | ft. | |
| ” pass, | 15,000 | ” | |
| ” base, | 1000 | ” | (Delhi.) |
| Alps. | |||
| Mont Blanc, | 14,500 | ft. | |
| Height of pass, | 7200 | ” | |
| ” base, | 1200 | ” | |
| Andes. | |||
| Chimborazo, | 21,000 | ft. | |
| Height of pass, | 10,000 | ” | |
| ” base, | (Sea.) | ||
| Pyrenees. | |||
| Maladetta, | 10,722 | ft. | |
| Height of pass, | 8000 | ” | |
| ” base, | (Sea.) | ||
In the Alps and Caucasus the relation of the height of the pass to the height of the chain is as 1 to 2; in the Himalaya, Quito Cordillera, and Alleghany Mountains, as 1 to 1·8; in the Pyrenees and Cordillera of Bolivia, as 1 to 1·5. In the Alps, therefore, where the pass is only half as elevated as the chain, the communication is the most direct, and the least barrier is put to the purposes of man,—a fact of great import in relation to human culture. The Pyrenees are in direct contrast in this respect, the most unapproachable, the most sundering of mountains.
The position of mountain chains is a matter of the first importance in relation to the welfare of man, and the solution of many of the most important problems in history. Whether interior ranges like the Ural and the Atlas, or ranges connecting two seas like the Caucasus, or those like the Mexican Sierras, lying between two oceans, are most open to human approach and use, is a question which we will not here stop to consider; but it may be said that, whether situated in the relations just indicated, or whether they are meridianal ranges like the Ural, the Scandinavian chain, the Alleghanies, or the great Cordillera of both Americas, which extends from the tropical world to both polar zones; or whether they run in the same direction with the parallels of latitude, turning one side to the colder north, and another side to the sunnier south; or whether they assume a diagonal direction like the Swiss Alps, from southwest to northeast, or like the Caucasus, from northwest to southeast, is a matter of the first importance to ascertain. Of not less consequence is it to discover whether the chain is the edge or rim of a plateau, and can have, therefore, only a one-sided development, like the Himalayas toward the south, or the Anti-Taurus toward the north, because the existence of a plateau on the reverse side dwarfs the slant distance, and gives but a fractional part of what, without the plateau, would be open and clear.
As plateaus usually display this edge on both sides, the border has been aptly compared to a double ledge or rim, between the two sides of which the table-land lies, often tolerably high above the sea level. If these rims, like mountains, are not contiguous to the plateau; if they are separated from it by a valley of greater or less width and depth, running parallel with the edge, they form what Humboldt has called natural circumvallations. Of such the Altai range, on the north side of the Asiatic central plateau, is an example. The hollow between the range and the plateau just mentioned is partly filled with inland seas. The Caucasus may, in like manner, be regarded as the circumvallation of the American plateau, separate from it by the Koor and the Aras (ancient Araxes) rims. Yet in the Caucasus another modification occurs—a partial linking of the plateau with the range at the west extremity, by the connecting chain of the Moschic Mountains. In like manner the Pyrenees, in their eastern half, form a circumvallation around the north side of the Castilian plateau, separated from it by the basin of the Ebro, and forming a perfect ring around Upper Castile and the elevated province of Biscay.
In cases where a mountain chain rests upon a plateau, rising up in the very heart of it, its summits seem to be not high, although the basis, the true foot of the chain, may not be at the level of the plateau, but far lower, and such mountains may, therefore, be of great absolute height. The name superimposed mountains has been given to them. Such are the Kuenlun and the Thian-Shan ranges of Central Asia, the Guadarrama chain between Old and New Castile, and the Rocky Mountains in North America. These superimposed ranges often run near to and parallel with the rim or edge of the plateau, and seem to give it more completeness and breadth.