or Mainland, an island of Scotland, the largest of the Orkneys, lies about the centre of the group. It is about 20 miles in length, and its breadth varies from 3 to 15; area, 150 square miles. In shape it is very irregular, being penetrated on all sides by arms of the sea, so that no part of the land is more than 4 or 5 miles from the sea. The western and north-western coasts are steep and lofty; the waves of the Atlantic roll in and dash upon the rocks with such violence that several remarkable caves have been hollowed out by them. The surface gradually slopes towards the south-east, and is diversified with hills and valleys, though bare of trees, and consisting chiefly of moors and mosses. There are, however, sheep pastures and some fertile tracts of ground. The geological structure of the greater part of the island is old red sandstone, containing many fossil fishes. There are also some dykes of whinstone, and a range of granite hills, forming a promontory on the west coast. Oats, beans, and bere are the crops principally raised on the island. Grouse, plover, and other kinds of game abound here, as well as fish. The island has several good harbours, and the only towns in Orkney, Kirkwall and Stromness. It is divided into 13 parishes. Pop. (1851) 16,757.