Examples of dolomitization may be obtained in practically every geological formation in which limestones occur. The oldest rocks are most generally affected, e.g. the Cambrian limestones of Scotland, but the change occurs, as has already been stated, even in the upraised coral reefs of the Indian and Pacific oceans which are very recent formations. It is very interesting to note that dolomites are very frequent among rocks which indicate that desert or salt-lake conditions prevailed at the time of their deposit. The dolomite or magnesian limestone of the English Permian is an instance of this. The explanation may be found in the fact that the waters of bitter lakes are usually rich in magnesium salts which, percolating through beds of limestone, would convert them into dolomite. Among the most famous dolomites are those of the Dolomite Alps of Tirol. They are of Triassic age and yield remarkably picturesque mountain scenery; it is believed that some were originally coral reefs; they are now highly crystalline and often contain interesting minerals and ores. The galena limestone of the North American Trenton rocks is mostly a dolomite.
Dolomites furnish excellent building stones, and those of the north-east of England (Mansfield stone, &c.) have long been regarded with great favour on account of their resistance to decomposition. They vary a good deal in quality, and have not all proved equally satisfactory in practice. Part of the Houses of Parliament at Westminster is built of dolomite. (J. S. F.)
DOLOMITES, THE, a mountain district in the South Tirolese Alps, though sometimes it is erroneously considered to form part of some other chain than the Alps. The distinguishing feature of this district is that it is composed of magnesian limestone, which rises in peaks of a most singular degree of sharpness and streaked by veins of the most startling colours. Nowadays it has become well known to tourists, who, however, keep mainly to a few great centres, though most of the more striking peaks were first ascended in the late sixties and early seventies of the 19th century by English mountaineers. Roughly speaking the Dolomite region lies between the Brenner railway from Franzensfeste to Trent (W.) and the road over the Monte Croce Pass from Innichen in the Drave valley by way of the Sexten glen and the Piave valley to Belluno and Feltre (E.). On the north it is limited by the railway line from Innichen to Franzensfeste, and on the south by the railway and road from Trent to Feltre. The highest summit is the Marmolata (10,972 ft.), but far more typical are the Sorapiss, the Cimon della Pala, the Langkofel, the Pelmo, the Drei Zinnen, the Sass Maor and the Rosengarten (see ALPS). Among the chief tourist resorts are St Ulrich (in the Gröden valley), San Martino di Castrozza (near Primiero), Caprile and Cortina d'Ampezzo.