ARDNAMURCHAN (-mur´_h_an) POINT, the most westerly point of the Island of Great Britain, in Argyllshire, having a lighthouse, 180 feet above sea-level, visible 18 to 20 miles off.
AR´DOCH, a parish in south Perthshire, celebrated for its Roman remains, one, a camp, being the most perfect existing in Scotland.
ARDROSS´AN, a seaport of Scotland, in Ayrshire, on the Firth of Clyde. It has a large harbour and shipbuilding yards, and is a centre of steamship services with Arran, Ireland, and Douglas, I.O.M. Pop. (1921), 7214.
ARDS´LEY, East and West, an urban district or town of England, W. Riding of Yorkshire, several miles north-west of Wakefield, with collieries, iron-mines, ironworks, &c. Pop. (1921), 7058.
ARE (är), the unit of the French land measure, equal to 100 sq. metres, or 1076.44 English sq. feet. A _hectare_ is 100 ares, equal to 2.47 English acres. The tenth part of an are is called a _déciare_, and a hundredth part a _centiare_.
A´REA, the superficial content of any figure or space, the quantity of surface it contains in terms of any unit. See _Mensuration_.
ARE´CA, a genus of lofty palms with pinnated leaves, and a drupe-like fruit enclosed in a fibrous rind. _A. Cat[)e]chu_ of the Coromandel and Malabar coasts is the common areca palm which yields areca or betel-nuts, and also the astringent juice catechu. _A. olerac[)e]a_ is the cabbage tree or cabbage palm of the West Indies. With lime and the leaves of the betel-pepper, the areca-nuts when green form the celebrated masticatory of the East. They are an important article in Eastern trade.
ARECIBO ([.a]-re-th[=e]´b[=o]), a seaport town on the north coast of the Island of Porto Rico. Pop. 9612.
ARE´NA, the enclosed space in the central part of the Roman amphitheatres, in which took place the combats of gladiators or wild beasts. It was usually covered with sand or saw-dust to prevent the gladiators from slipping, and to absorb the blood. See _Amphitheatre_.
ARENACEOUS ROCKS include all sediments in which quartz sand is the most important constituent. Owing to its resistance to comminution and to chemical attack, quartz accumulates in sea-beaches while other mineral matter becomes removed. Hence sands gather near a shore and ultimately become consolidated by various natural cements into sandstones, those cemented by silica being styled quartzites. Sand-dunes in deserts or on coasts are unconsolidated arenaceous rock-masses.