III.

Structure and Climate

The Pyrenees, which are older than the Alps, were formed mainly during the Palaeozoic and Mesozoic eras. The eastern half of the Pyrenees is composed mostly of granite and gneiss, whereas in the western half the lower slopes are made up of limestone and the peaks of granite.

The Pyrenees are a climatic divide; the French slopes receive abundant precipitation, while the Spanish slopes have very little. Vegetation is most developed in the west, where the lower slopes are forested; in the east the mountains are almost entirely barren. The permanent snow line is at about 1,829 m (6,000 ft), and small glaciers are found in the high central section. Characteristic of the French Pyrenees, which are generally much steeper than the Spanish Pyrenees, are gaves, torrents that often drop from cliffs to form spectacular waterfalls.