The foundation walls of a city building above the footing course, are usually built of stone. Concrete is used to some extent, and brick will be used for the party wall where there is to be a cellar both sides. For heavy walls of build-ings, three or more stories in height, it will be necessary to use block stone. These are stones roughly fashioned to dimension and generally laving from eighteen inches to two feet in height and the full width of the wall. (Fig. 101.) Being brought nearly even and square, not much mortar will be used, and this should be of clear cement and sand below the grade line.