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LEFT ABDXC/KE 240 ABEOMETEB On Nov. 3, 1916, the First American Army destroyed the Mezieres-Metz rail- way, and Nov. 6 gained the heights of the Woevre and Sedan. On Nov. 9 the French invested Mezieres. See World War. ARDMORE, a city of Oklahoma, the county-seat of Carter co. It is on the Santa F^, the Rock Island, San Fran- cisco and Oklahoma, and the New Mexico and Pacific railroads. It has several im- portant educational institutions. Its chief industries are cotton and asphalt. There are important oil wells and de- posits of natural gas in the neighbor- hood. It is also the center of an impor- tant stock-raising and agricultural com- munity. Pop. (1910) 8,618; (1920) 14,181. ARD NAM UR CHAN (-mur'kan) 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. ARDOCH, a parish in south Perth- shire, celebrated for its Roman remains, one, a camp, being the most perfect ex- isting in Scotland. ARE, the unit of the French land measure, equal to 100 square meters, or 1,076.44 square feet. A hectare is 100 ares, equal to 2.47 acres. ARECA, a genus of lofty palms with pinnated leaves, and a drupe-like fruit inclosed in a fibrous rind. A. catechu, of the Coromandel and Malabar coasts, is the common areca palm which yields areca or betel nuts, and also the astrin- gent juice catechu. A. oleracea is the cab- bage 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 (ar-a-se'bo), an important commercial town of Porto Rico; on the N. coast; facing the Atlantic Ocean; 50 miles W. of San Juan. Tributary to the town is a district of about 30,000 inhabi- tants. Pop. (1920) 10,039. ARENA, the inclosed space in the central part of the Roman amphitheaters, in which took place the combats of gladiators of wild beasts. It was usually covered with sand or sawdust to prevent the gladiators from slipping, and to ab- sorb the blood. ARENACEOUS ROCKS, rocks com- posed entirely, or to a large extent, of grains of quartz. Beds of loose sand oc- cur extensively in the more recent de- posits. Silvery flakes of mica are sel- dom absent; and they often occur in lay- ers parallel to the planes of stratification, causing the rock to split into thin slabs, and exposing a glittering surface. These are called micaceous sandstones. When grains of feldspar occur, itisafeldspathic sandstone. Often large quantities of cal- careous matter, either as cement or as distinct grains, occur; and these are called calcareous sandstones. In like manner we have siliceous and ferrugi- nous sandstones, when silica and oxide of iron are conspicuously present as cement- ing or binding materials. Clay and car- bonaceous matter, when plentifully dif- fused through the rock, give rise to argillaceous, carbonaceous, and bitumi- nous sandstones. Greensand, or glau- conitic sandstone, is a rock con- taining abundant grains of the dirty greenish mineral called glauconite. Arkose is a sandstone composed of dis- integrated granite; volcanic sandstone, trappean sandstone, etc., being composed of disintegrated igneous rocks. A sand- stone of homogeneous composition, which may be worked freely in any direction, is called freestone or liver rock. Flag- stone is a sandstone which is capable of being split into thin beds or flags along the planes of deposition. When the sand- stone is coarse-grained, it is usually called grit. If it contain, more or less abun- dantly, grains large enough to be called pebbles, the sandstone is said to be con- glomeratic; and if the pebbles or stones be angular, the rock is described as a brecciiform sandstone. Coarse-grained grits and pebbly or conglomeratic sand- stones pass into conglomerate or pudding- stone, which consists of a mass of various- sized water-worn stones. Brecciiform sandstones frequently pass into breccia, which is an aggregate of angular and sub-angular fragments. Graywacke is an argillaceous sandstone, more or less al- tered and sometimes semi-crystalline, met with among palaeozoic formations. AREOLAR TISSUE, a tissue widely diffused through the body, and composed of white and yellow fibers, the former im- parting to it strength, and the latter elasticity. Areolar tissue protects from injury the parts of the body in which it occurs, and when placed in the interstices of other tissues it keeps the latter from moving as freely as otherwise they would. The cutis vera, or true skin, is composed of it. AREOMETER (ar-e-om'e-ter), an instrument designed to measure the specific gravity of liquids. The simpler areometers measure only the relative weights of liquids. They consist of a