FOUNDATIONS

are the natural earth-bed, rock, or other substance upon which the walls of a building rest. In selecting the site for a structure it is first of all nece ary to examine the nature of the ground, and if a substantial natural f. cannot be reached at a moderate depth it must be provided by artificial means (e.g. by piles or concrete). Rock is the best natural f.; certain kinds of clay also serve the purpose; and sand and gravel likewise po e good weight bearing qualities, but these latter are subject to the action of ‘scour,’ (7.e.) disintegration by water. Then, sometimes, the ground itself is of an artificial character, which means that at some period a hollow has been filled in with waste material, and where this is encountered it. is always nece ary to go deeper until a substantial natural f. is reached. A bed of concrete is now the method usually employed to provideaf. where the ground is found insufficient to support a building; and the alternative to this is the use of piles, which are driven deep into the soil, and upon the heads of which a timber platform is laid; piles are used in canal-cities like Venice and Amsterdam. Stone footings to the walls are also sometimes used,