Caithness, a county occupying the extreme north-east of Scotland, bounded W. and S. by Sutherlandshire, E. by the North Sea, and N. by the Pentland Firth. Its area is 446,017 acres, or nearly 697 sq. m. The surface generally is flat and tame, consisting for the most part of barren moors, almost destitute of trees. It presents a gradual slope from the north and east up to the heights in the south and west, where the chief mountains are Morven (2313 ft.), Scaraben (2054 ft.) and Maiden Pap (1587 ft.). The principal rivers are the Thurso ("Thor's River"), which, rising in Cnoc Crom Uillt (1199 ft.) near the Sutherlandshire border, pursues a winding course till it reaches the sea in Thurso Bay; the Forss, which, emerging from Loch Shurrery, follows a generally northward direction and enters the sea at Crosskirk, a fine cascade about a mile from its mouth giving the river its name (fors, Scandinavian, "waterfall;" in English the form is force); and Wick Water, which, draining Loch Watten, flows into the sea at Wick. There are many other smaller streams well stocked with fish. Indeed, the county offers fine sport for rod and gun.

The lochs are numerous, the largest being Loch Watten, 2¾ m. by ¾ m., and Loch Calder, 2¼ by 1 m., and Lochs Colam, Hempriggs, Heilen, Ruard, Scarmclate, St John's, Toftingale and Wester. So much of the land is low-lying and boggy that there are no glens, except in the mountainous south-west, although towards the centre of the county are Strathmore and Strathbeg (the great and little valleys). Most of the coast-line is precipitous and inhospitable, particularly at the headlands of the Ord, Noss, Skirsa, Duncansbay, St John's Point, Dunnet Head (346 ft.), the most northerly point of Scotland, Holburn and Brims Ness. From Berriedale at frequent intervals round the coast occur superb "stacks," or detached pillars of red sandstone, which add much to the grandeur of the cliff scenery.

Caithness is separated from the Orkneys by the Pentland Firth, a strait about 14 miles long and from 6 to 8 miles broad. Owing to the rush of the tide, navigation is difficult, and, in rough weather, dangerous. The tidal wave races at a speed which varies from 6 to 12 m. an hour. At the meeting of the western and eastern currents the waves at times rise into the air like a waterspout, but the current does not always nor everywhere flow at a uniform rate, being broken up at places into eddies as perilous as itself. The breakers caused by the sunken reefs off Duncansbay Head create the Bores of Duncansbay, and eddies off St John's Point are the origin of the Merry Men of Mey, while off the island of Stroma occurs the whirlpool of the Swalchie, and off the Orcadian Swona is the vortex of the Wells of Swona. Nevertheless, as the most direct road from Scandinavian ports to the Atlantic the Firth is used by at least 5000 vessels every year. In the eastern entrance to the Firth lies the group of islands known as the Pentland Skerries. They are four in number - Muckle Skerry, Little Skerry, Clettack Skerry and Louther Skerry - and the nearest is 4½ m. from the mainland. On Muckle Skerry, the largest (½ m. by ⅓ m.), stands a lighthouse with twin towers, 100 ft. apart.

The island of Stroma, 1½ m. from the mainland (pop. 375), belongs to Caithness and is situated in the parish of Canisbay. It is 2¼ m. long by 1¼ m. broad. In 1862 a remarkable tide climbed the cliffs (200 ft.) and swept across the island.