Footings of dwarf walls

Footings of dwarf walls shall be of concrete mixed in proportions not less than one part cement to six of broken stone and three of sand, and for walls 6 in. or less in thickness shall be not less than 6 in. deep and 1ft. 6 in. wide. For walls 9 in. in thickness footings shall be 2 ft. 6 in. wide. For walls 13 1/2 in. in thickness footings shall be 3 ft. wide. The bottom of footings shall be not less than 12 in. below ground level.