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• tunnels and underground excavations — ▪ engineering Introduction        Great tunnels of the world Great tunnels of the worldhorizontal underground passageway produced by excavation or occasionally by nature s action in dissolving a soluble rock, such as limestone. A vertical opening …   Universalium

• North America — North American. the northern continent of the Western Hemisphere, extending from Central America to the Arctic Ocean. Highest point, Mt. McKinley, 20,300 ft. (6187 m); lowest, Death Valley, 276 ft. (84 m) below sea level. 400,000,000 including… …   Universalium

• United States — a republic in the N Western Hemisphere comprising 48 conterminous states, the District of Columbia, and Alaska in North America, and Hawaii in the N Pacific. 267,954,767; conterminous United States, 3,022,387 sq. mi. (7,827,982 sq. km); with… …   Universalium

• Precambrian time — Interval of geologic time from с 3. 8 billion years ago, the age of the oldest known rocks, to 544 million years ago, the beginning of the Cambrian Period. This interval represents more than 80% of the geologic record and thus provides important… …   Universalium

• Indian Ocean — an ocean S of Asia, E of Africa, and W of Australia. 28,357,000 sq. mi. (73,444,630 sq. km). * * * Indian Ocean Introduction Indian Ocean Background: The Indian Ocean is the third largest of the world s five oceans (after the Pacific Ocean and… …   Universalium

• Dolaucothi Gold Mines — The Dolaucothi Gold Mines (grid reference SN662403), also known as the Ogofau Gold Mine, are Roman surface and deep mines located in the valley of the River Cothi, near Pumsaint, Carmarthenshire, Wales. The gold mines are located within the… …   Wikipedia

• Norwegian Campaign — Part of the Second World War German forces advancing near Bagn in Va …   Wikipedia

• cañada — /keuhn yah deuh, yad euh/, n. Chiefly Western U.S. 1. a dry riverbed. 2. a small, deep canyon. [1840 50; < Sp, equiv. to cañ(a) CANE + ada n. suffix] * * * Canada Introduction Canada Background: A land of vast distances and rich natural resources …   Universalium

• Canada — /kan euh deuh/, n. a nation in N North America: a member of the Commonwealth of Nations. 29,123,194; 3,690,410 sq. mi. (9,558,160 sq. km). Cap.: Ottawa. * * * Canada Introduction Canada Background: A land of vast distances and rich natural… …   Universalium

• France — /frans, frahns/; Fr. /frddahonns/, n. 1. Anatole /ann nann tawl /, (Jacques Anatole Thibault), 1844 1924, French novelist and essayist: Nobel prize 1921. 2. a republic in W Europe. 58,470,421; 212,736 sq. mi. (550,985 sq. km). Cap.: Paris. 3.… …   Universalium

• igneous rock — Any of various crystalline or glassy, noncrystalline rocks formed by the cooling and solidification of molten earth material (magma). Igneous rocks comprise one of the three principal classes of rocks, the others being metamorphic and sedimentary …   Universalium