Ivory is an opaque, creamy white, hard, fine-grained, modified dentin that composes the upper incisor teeth of an elephant. Ivory is composed of curved layers of dentine alternating in shade, that intersect one another; the resulting lozenge-shaped structure is elastic and finely grained. The layers of a tusk are deposited from the central pulp, so that the innermost layer is the newest. Most commercial elephant ivory is obtained from the tusks of the African elephant, mainly from eastern and central Africa. (Most of the ivory of the western half of Africa is hard, whereas that from the eastern half is soft. Hard ivory is glassier in texture, harder to cut and more likely to crack than soft ivory.)
Fossil ivory, called odontolite, is a blue variety that is found in small quantities in the frozen soil of northern Siberia. Odontolite was produced by the mammoths of the Pleistocene geological epoch; its blue colour results from saturation by metallic salts. Carved ivory has been used for decorative purposes since the time of the ancient Egyptians. Small pieces of ivory are used for high-quality furniture inlays, chess pieces, and small jewellery. Larger pieces of ivory sometimes have been used in the manufacture of billiard balls, piano keys, and toilet articles.
During the late 1980s, as Africa's elephant herds declined, environmentalists led a world-wide effort to shut down the ivory trade; in 1989 the USA and the European Union banned all ivory imports. Tusks of several other animals such as hippopotamuses, narwhals, sperm whales, and walruses are commonly called ivory and have similar physical properties, and many plastic substitutes for ivory have been developed. Several ivory-like vegetable parts are also used in imitation of ivory; the ivory palm, for example, produces large, white, hard seeds, called ivory nuts, the endosperm of which is commonly known as vegetable ivory. In painting, ivory is a delicate colour deeper in tone than off-white, but not so deep as cream. Research Ivory
A plateau or tableland generally denotes a large stretch of highland which is practically the same height above sea-level, and which descends on all sides to lower ground. Some plateaux, however, such as those of Tibet and Bolivia, that are fringed by high mountain ranges which tower above the plateau level, are known as intermont plateaux. Sometimes they are so completely enclosed as to have no outlet to the sea.
A plateau might be regarded as an elevated plain, but there is often a great difference between the surface of a plain and that of a plateau. As a plateau is high, rivers are swift and carve deep, narrow valleys instead of the broad, open valleys of the lower rivers of the plains. Such plateau areas as Wales and the Highlands of Scotland, are broken by deep, narrow valleys, and are termed dissected plateaux. On reaching the top of such an area one has a long view of a series of flat-topped mountain ridges. These ridges are all of approximately the same height, and if one imagines the clouds descending until they touched one ridge, then almost every other ridge would be similarly cloud-capped. Other good examples of plateaux are Tibet in Asia, the Ecuador and Bolivian plateaux in South America, and nearly the whole of the continent of Africa.
The Deccan of India is a plateau that has been tilted so that the western edge is much higher than the eastern edge, and all the main rivers drain eastwards. In many instances plateaux are formed by the denudation or wearing down of higher mountainous areas. Ultimately, such areas may become so low that they are nearly plains, i.e. peneplains, such as the land around HudsonBay. Millions of years ago lava was forced up through cracks in the earth's crust, and spread out over the land in great sheets which have since hardened to form plateaux of basalt.
Two well-known examples of such plateaux are in Antrim (Ireland), and on the Deccan of India to the east of Bombay. Many of the most extensive areas of plateaux in the world are composed of very hard old rock. The GuianaHighlands, most of Africa, Arabia, the Deccan of India, and the West Australian plateaux are all composed of rocks of similar age. The ancient plateau lands are principally valuable for their minerals, such as the gold of Western Australia; the iron and manganese of the Brazilian Highlands; the gold, copper, and diamonds of the African plateau; and the gold of the Lena plateau in Siberia. Where plateaux are found in tropical areas they are important because, being cooler than the neighbouring lowlands, they offer greater possibilities for successful European settlement and development. The highlands of Brazil, Kenya, and Tanganyika are illustrations of this. Much of the tropical plateau area is covered by savannah grasslands. Most of these areas are not yet developed, but offer possibilities for the production of a large variety of both animal and vegetable products when communications have been developed and further settlement has taken place. Research Plateau
Bearberry (Arctostaphylos uva-ursi) is an evergreen shrub of the heath family growing on the barren moors of Scotland, Northern Europe, Siberia, and North America. The leaves, under the name of uva ursi, were formerly used in medicine as an astringent and tonic. Research Bearberry
Bewick's Swan (Cygnus colombarius) is a small (roughly 120 cm long) Siberian swan similar in appearance to the Whooper Swan, but with less yellow on its bill. During the winter they migrate in family groups within flocks to Britain before returning to Siberia when the weather becomes warmer. Research Bewick's Swan
A chipmunk is a species of ground squirrel of the genus Tamias common in Siberia and North America. The possess internal cheek pouches and are characterized by their colouration, the back being marked by alternate light and dark bands. Research Chipmunk
Abbreviations
Research Ivory
