Wherever terraces or lawns need the support of a small retaining wall, concrete is excellent for this purpose. The foundations of such walls should be carried down below the frost -line. The usual mixture is 1 : 2 : 4. Drains should be built at intervals along the lower part of the wall, to allow the seeping ground water to come out. At intervals of about every 25 feet expansion joints should be made, somewhat the shape of the tongue and groove in flooring. The base of such a retaining wall should be at least as wide as 4/10 the height of wall.