33 a and 33 b and a cap wall 54 all of which together define the shape and outside dimensions of block 31 face wall 50 extends upwardly from base 45 and is better shown in fig2 a face wall 50 has a raised side lip 44 near the intersection of side wall 33 a and a groove 42 recess into the edge near the intersection of the opposite edge of face wall 50 and side wall 33 b raised side lip 44 and groove recess 42 provide a means for aligning blocks 31 side by side such that a raised side lip 44 of a first block fits securely into a width recess 42 of a second adjacent block thereby preventing forward movement of a side of the second block 31 against a side of a first block 31 and also obscuring from view any gap formed by space between the side walls of pair of adjacent blocks 31 referring again to fig2 a the upper surface shown in the top view of cap wall 54 has a plurality of set back holes 35 a and 35 b near the intersection of face wall 50 and side walls 33 a and 33 b aligned generally along the length of walls 33 a and b individual ones of setback holes 35.