Pyrenees

The tectonics of the Pyrenees are still only imperfectly under stood. Some authorities consider the structure to be that of a "fan," whilst others have shown that the phenomena of recouvre meat play an important part here. Large masses of rock have been brought forward upon thrust-planes over the edges of other beds with which they originally had no connection. Several cases have been described; but denudation has been carried further than in the Alps, and accordingly the masses overlying the thrust-planes have been more completely removed.

The Pyrenean axis was outlined by the Hercynian movement and folding took place along it at the close of the Dinantian epoch and again before the Permian. Later the chain was com pletely submerged until early Cretaceous times, when the earth movements which raised the present mountains commenced and continued into the Oligocene period. The uplift of the Pyrenees was therefore completed before that of the Alps.

The arrangement of the Pyrenees in chains gently inclined near the centre but longitudinal everywhere else, is illustrated by the courses of the streams which flow down towards Spain. On the French side most of the longitudinal valleys have disappeared, except at the eastern end. On the south the principal streams, after cutting their way through the highest zone at right angles to the general direction of the range, become involved half-way to the plains in great longitudinal folds, from which they make their escape only after traversing long distances.

The total area of the Pyrenees is estimated at 21,044 sq.m., two thirds of which is on the southern versant. The mean eleva tion is placed at 3,93o ft., whilst the highest summit Pic de Nethou, is 11,168 ft. above sea level. The passes show a greater altitude than those of the Alps.

Gaves.

Four features of Pyrenean scenery are the absence of great lakes, as in the Alps ; the rarity and great elevation of passes; the large number of the mountain torrents locally called gaves, which often form lofty waterfalls, surpassed in Europe only by those of Scandinavia; and the frequency with which the upper end of a valley assumes the form of a cirque. The highest waterfall is that of Gavarnie (1,515 ft.), at the head of the Gave de Pau; the Cirque de Gavarnie, in the same valley, is perhaps the most famous example of the cirque formation. Low passes only occur at the two extremities of the range, where the principal highroads and railways run between France and Spain; a third railway (Pau to Jaca via the pass of Somport) was opened in 1928. In the mountains themselves there are only five passes practicable for motors—the Col de la Perche, Col du Pourtalet, Col de Somport, Roncevalles road and the road through the Baztan valley.

Projects for further railway construction, including the build ing of tunnels on a vast scale, have been approved by the French and Spanish governments (see SPAIN : Communications).

The metallic ores of the Pyrenees are not important. There are considerable iron mines at Vicdessos in Ariege and at the foot of Canigou in Pyrenees-Orientales. Coal deposits capable of being profitably worked are situated chiefly on the Spanish slopes and the French side has numerous bedsof lignite. Mineral springs

aYe abundant and specially noteworthy are the hot springs. The latter, among which those of Bagneres de Luchon and Eaux Chaudes may be mentioned, are sulphurous and mostly situated high, near the margin of the granite. The lower springs, such as those of Bagneres de Bigorre (Hautes-Pyrenees,), Rennes (Aude) and Campagne (Aude), are mostly selenitic and not very warm. The use of hydro-electric power has been developed in recent years.

The amount of the precipitation, including rain and snow, is much greater in the western than in the eastern Pyrenees, causing a marked contrast between these sections of the chain in more than one respect. In the first place, the eastern Pyrenees are without glaciers, the quantity of snow falling there being insuf ficient. The glaciers are confined to the northern slopes of the central Pyrenees, and do not descend far down in the valleys, but have their greatest length in the direction of the chain. They form, in fact, a narrow zone near the crest of the highest mountains. Here, as elsewhere in Europe, there are evidences of a much wider extension of the glaciers during the Ice Age. The best known glacier is that in the valley of Argeles. The snow-line varies in different parts of the Pyrenees from 8,800 to 9,200 ft. above sea-level.

A more marked effect of the high rainfall in the west is seen in the vegetation. The lower mountains in the extreme west are very well wooded, but the extent of forest declines eastwards, and the eastern Pyrenees are peculiarly wild and naked, more so because here the granite massifs occur. There is a change, more over, in the type of flora in passing from west to east. In the west the flora, at least in the north, resembles that of central Europe, while in the east it is distinctly Mediterranean in char acter. The Pyrenees are relatively as rich in endemic species as the Alps, and among the most remarkable instances of this is the occurrence of the sole European species of Dioscorea (yam), the D. pyrenaica, on a single high station in the central Pyrenees, and that of the monotypic genus Xatardia, only on a high pass between the Val d'Eynes and Catalonia. The genus most abun dantly represented in the range is that of the saxifrages, several species of which are here endemic.

In their fauna also the Pyrenees present some striking in stances of endemism. There is a distinct species of ibex (Capra pyrenaica) confined to the range, while the Pyrenean desman or water-mole (Mygale pyrenaica) is found only in some of the streams of the northern slopes of these mountains, the only other member of this genus being confined to the rivers of southern Russia. Among the other peculiarities of the Pyrenean fauna are blind insects in the caverns of Ariege, the principal genera of which are Anophthalmus and Adelops.

The ethnology, folk-lore, institutions and history of the Py renean region form an interesting study : see ANDORRA; ARAGON ; BASQUE PROVINCES ; BEARN ; CATALONIA ; NAVARRE.