Rubble Concrete masonry will consist of Class III. Concrete, as specified under "Concrete," Item 32, in which are firmly imbedded rubble stones to an extent of not over one-half ( 1/2) the volume of the wall. The rubble stones must be clean, sound, hard stone not over two cubic feet in volume each, nor less than one-half ( 1/2) cubic foot. The rubble stones shall be at least four (4) inches apart and with no points thereof closer than four (4) inches to any face of the wall. The resulting masonry must be solid and free from voids. In all other respects the specifications and manner of payment of "Concrete Masonry," Item 33 shall govern.