In size, Shetland ranks fifteenth among the Scottish counties; but in population only twenty-seventh. The total area (excluding water) is 352,319 acres or 550½ square miles. The group consists of about one hundred islands, of which twenty-nine are inhabited. The largest is Mainland, which embraces about three-fourths of the whole land-surface; and the others, in point of size, are Yell, Unst, Fetlar, Bressay and Whalsay. Yell measures 17½ miles by 6½, Unst 12 by nearly 6. The smaller islands include East and West Burra, Muckle Roe, Papa Stour, Skerries, Fair Isle and Foula; the remainder consisting of islets, holms, stacks and skerries. From Fair Isle, which lies about mid-way between Orkney and Shetland, to Sumburgh Head, is 20¼ miles; and from that point to Flugga in Unst, in a straight line, is 71 miles. From Sumburgh Head to Fethaland, the most northerly part of the Mainland, is 54 miles; and the greatest breadth, from the Mull of Eswick to Muness, is about 21 miles. Including Fair Isle and Foula, the group lies between the parallels of 59° 30´ and 60° 52´ north latitude; and between 0° 43´ and 2° 7´ west longitude. The general trend of the islands is north-easterly, and their position in relation to the mainland of Scotland is also in that direction; Sumburgh Head being 95 miles north-east of Caithness and 164 miles north of Aberdeen. The North Sea washes the eastern sea-board, and the Atlantic Ocean the western; sea and ocean join forces between Sumburgh Head and Fair Isle to form that turbulent tideway called the “Roost.” They also meet north of Yell and Unst, where the Atlantic sets strongly through Yell Sound and Blue Mull Sound for six hours during flood tide, and the North Sea, in its turn, in the opposite direction for the other six hours. 4. Surface and General Features The surface of the larger islands is hilly, and the general direction of the ridges is north and south, corresponding to the length of the islands. The inland parts present an undulating surface of peat bogs and moorland, dotted here and there with fresh-water lochs, which accentuate, rather than relieve, the monotony of the landscape. The hills are round or conical in shape and of moderate height, ranging from 500 to 900 feet. Unlike the rounded hills of the Lowlands of Scotland, which are often grassy to the top, most of the Shetland hills are brown and barren, being covered with heather and moss or short coarse grass. Neither have they the rugged grandeur of the Highlands, for the sides are generally smooth and rounded, the result of intense glaciation.