BASIN

a term of comparatively recent use in physical geography, is generally used in relation to rivers, lakes, and seas, and designates not only the ground actually covered by them, but the whole area of the countries which send their drainage to them. Thus, for example, the basin of the Baltic means not merely the expanse of water to which that name is given, but all those parts of Grermany, Ru ia^ Sweden, and Denmark drained by rivers and lakes which discharge themselves into the Baltic. The boundary between two basins, formed for the most part by a ridge or plateau interposed between them, and sending the waters which descend from its sides in opposite directions, is called the watershed. In geology the term basin is sometimes employed to designate, not an area of drainage, but an area occupied by a particular formation. Thus we speak of the Paris basin and the London basin. In a still more restricted sense, a coal-field is sometimes designated a coal-basin, because in many cases the area over which coal-seams extend has more or le of the shape of a basin.