846 ORKNEY AND SHETLAND of which twenty-nine are inhabited, the others, which are called "holms," being frequently made use of for pasture. Besides Pomona or the Mainland, which has an area equal to all the others combined, the principal islands are, to the north, Rousay, Westray, Papa-Westray, North Ronaldshay, Sanday, Eday, Stronsay, and Shapinshay, and to the south, Hoy, North Walls, South Walls, Flotta, South Ronaldshay, and Burray. The members of the Shetland group are more numerous than the Orkneys, consisting of about a hundred islands and islets ; besides the Mainland, the more important are Yell, Unst, and Fetlar to the north, Whalsay and Bressay to the east, and East and West Burra, Papa-Stour, Muckle Roe, and Foula to the west. Except towards the west the surface of the Orkneys is comparatively flat, and in some cases, as in Sanday, the coast is so low as to be a frequent cause of shipwreck. The island of Hoy consists principally of lofty black barren rocks, of which the Ward Hill attains a height of 1564 feet. In the southern part of the Main land, to the west of Kirkwall, the hills also reach a con siderable elevation, the highest summits being Wideford Hill near Kirkwall (740 feet) and the Ward Hill of Orphir (880 feet) ; and there is another hilly region in the north west of the Mainland, opposite the island of Rousay. The centre of Rousay is occupied by hills of considerable height. On the west of Hoy perpendicular precipices of great height descend sheer to the Atlantic. The outline of the islands is very irregular, and through the numerous firths and sounds the tides rush with great rapidity, forming occa sionally whirlpools called roosts, which in stormy weather frequently suck in fishing-boats and prove dangerous even to large vessels. The coast -scenery of the Shetland group is strikingly picturesque. The islands present an irregular rocky surface generally rising into hills of considerable elevation, the highest summit being Roeness Hill (1475 feet) in the Mainland. By the action of the waves the rocks have been worn into numerous fantastic shapes, and the coast-line is also deeply indented by bays and "voes" or sea -lochs, caused partly by denudation and partly by glacial action. The greater part of the coast is stern and precipitous, but Sumburgh Head, the Noup of Noss, Fitful Head, the island of Papa-Stour with its surrounding rocks, Foula (especially on its western side), the Drongs and adjoining rocks of the parish of Northmavine with the coast-line from Roeness Voe to Haevdadal Head, and Unst the most northern of the group may be singled out for their picturesque beauty or impressive grandeur. The action of the sea has formed numerous caves, the more remarkable of which are the immense Orkneyman s Cave near the Bard of Bressay, and the fantastic caves of Papa-Stour. Geology. The geological formation of the Orkneys is very similar to that of the adjoining mainland, and con sists almost entirely of the lower Old Red Sandstone of the flagstone series. A red and yellow sandstone series occupies part of Sanday, Eday, Burray, Flotta, and South Ronaldshay, and a long narrow strip of the Mainland to the south of Kirkwall. The mountainous district of Hoy be longs to the upper Old Red Sandstone, in which are inter- bedded volcanic rocks consisting of amygdaloidal lavas and ashes, and forming the terraces of the northern slopes of the Hoy hills. These rocks rest unconformably on the lower Old Red Sandstone. North-west from Stromness Bay to Inga Ness there is an outcrop of crystalline rocks consisting of granite and micaceous gneiss. The flagstone series, especially in the neighbourhood of Stromness, contains numerous fossils, ich thy elites, crustaceans, and plants being all represented. From the character of the striated surfaces of the rocks, and the presence of foreign rocks in the boulder-clay, it has been concluded that the Orkneys were subjected to a glacial action crossing from the North Sea to the Atlantic ; and there are also traces of local glaciers, especially at Hoy. The geological formation of the Shetland s, like that of the Orkneys, belongs principally to the lower Old Red Sandstone and the metamorphic rocks on which they rest unconformably ; but the proportion between the two species of rocks is reversed, the metamorphic rocks cropping to the surface throughout the greater part of the Shetland group. The central portion of the islands, including the north western half of the Mainland and its eastern seaboard in the parish of Northmavine, Whalsay, Yell, and the western seaboard of Unst, is occupied chiefly by micaceous and hornblendic gneiss with limestones and quartzites. In the southern portion of the Mainland the clay-slate series, Avith associated limestones and quartzites, prevails. In Unst and Fetlar there are large masses of serpentine and gabbro, and diorite occupies a large area in the districts of Delting and Northmavine. The lower Old Red Sandstone occupies the islands of Foula and Bressay, skirts the eastern sea board of the Mainland from Lerwick southwards, and in cludes the greater part of Walls. It is associated with a series of igneous rocks, especially in the western district of Northmavine, and there is also an intrusive series. Even more striking evidence of glacial action exists in Shetland than in Orkney. The metamorphic rocks are very rich in beautiful minerals, especially along the coast of North mavine, among the varieties being f elsite, epidote, actinolite, serpentine, anthophyllite, fluor-spar, steatite, magnetite, and cyanite. Both in Orkney and Shetland there are large deposits of peat. Climate and Agriculture. The temperature, both of the Orkneys and of the Shetlands, presents smaller variations than that of Scotland or England. The yearly average is- a little over 45 Fahr., the average for the coldest months
