The islands of Scotland are very numerous, and, in many instances, are large and important. The greatest archipelago, that of the Hebrides, extends along nearly the whole west coast of the mainland. It is broadly distinguishable into two divisions, the outer and the inner, but is capable of subdivision into live groups. Three of these press close upon the coast, the group of Isla and Jura on the south, that of Mull in the centre, and that of Skye on the north, – the last separated from the second by the seas which wash the far-projecting Point of Ardnamurchan on the mainland, and the first and second so concatenated as to admit a line of separation chiefly by their geognostic properties. The fourth, largest, most northerly, and far-stretching group, lies quite away from the mainland, and even from the group of Skye, separated from the northern part of the former by the Minch, and from the western skirts of the latter by the Little-Minch. It consists of about 140 islands and islets, about 140 miles in aggregate length, and lying so compactly as to be popularly viewed as one, and conventionally called the Long-Island. The fifth group is very small, lies to the far-west in profound loneliness, amidst a desert of waters, and draws attention chiefly by the romance of its situation and character, – consisting only of St. Kilda, itself more an islet than an island, and a tiny sprinkling on the bosom of the sea around it of dark, coarse gems, which pendulate between the character of islets and that of mere rocks. These groups are all fully treated in the article HEBRIDES. Another archipelago, that of Orkney, is separated at its south end by the Pentland frith, 6 miles broad from the north coast of Caithness, or extreme north of the mainland of Scotland. Its islands and islets lie somewhat compactly; but are divisible into two groups, the larger and more compact on the south, the smaller and more dispersed on the north-east, – the two separated by a sound which bears on the east side the name of Stronsa frith, and on the west side that of Westra frith. A full general description of the whole will be found in the article ORKNEY. An islet called Stroma, lies in the Pentland frith, 4 miles north-west of Duncansby-head. A third archipelago, that of Shetland, lies 48 miles north-north-east from Orkney. About two-thirds of their whole superficies are amassed in a very long island, of surpassingly irregular outline, and in several places very nearly dissevered, called the Mainland. Yell sound, a winding strait, separates this island on the south from the other chief island on the north, but is, in some places, thickly strewn with islets. One small island, Fowla, lies quite away to the west from the main group. Another, called Fair- Island, lies about half-way between that group and the Orkneys. All the details of a general description are given in the article SHETLAND. The other principal islands of Scotland are Mugdrum, in the frith of Tay; the Isle of May, Inchkeith, Cramond, Inchcolm, Inchgarvey, Inchmickry, Craigleith, Lamb, Fidra, and the Bass, in the frith of Forth, – the first and second the sites of lighthouses; and Arran, Bute, Great Cumbrae, Little Cumbrae, Pladda, Lady-Isle, and Ailsa-rock, in the frith of Clyde, – Pladda and Little Cumbrae the sites of lighthouses, and Lady-Isle the site of two beacon-towers. Of seaward rocks and sandbanks, the chief are Carrock, a beacon-station, 1½ mile north-east of Fifeness; Bell-rock, a dangerous ledge bearing aloft a lighthouse, 12 miles east of Buddonness; Marr’s-bank, a shoal, 30 miles east of the Bell-rock; Murray-bank, a sandbank 10 miles east of Montrose; the Long-Forties, a shoal, extending from the exterior side of Murray-bank, in a line nearly parallel with the coast, to within 70 miles of Kinnaird-head; Outer-Montrose-pits, a shoal, 90 miles east of Montrose; the Pentland-skerries, the site of a lighthouse, at the east end of the Pentland frith; Lappoch-rock, between Lady-Isle and Irvine harbour, in the frith of Clyde; and the Big and Little Scaurs, rocks at the middle of the entrance of Luce-bay.