34 similar in shape to the peripheral groove 28 as illustrated in fig1 the groove 28 39 fittingly receives and grips the wedge member 26 39 and the lip 22 39 of the right wall 18 39 of a first superposed block 10 39 in fig1 a a second superposed block 10 34 is mounted continuously with the first superposed block 10 39 on the block 10 the groove 28 34 grips the wedge member 26 34 and the lip 22 34 of the left wall 20 34 of the block 10 34 in another embodiment of the invention a block such as the top left corner block 37 in the assembly illustrated in fig3 does not have a central groove 34 the block 36 is equivalent to a block 10 separated in half about its center line 32 the two adjacent blocks 10 39 and 10 34 are connected together by a dovetail connection comprising a tenon 36 34 and a mortise 38 34 in the embodiment illustrated in fig3 to 10 the block 10 has a tenon 36 extending integrally from the left wall 20 and a mortise 38 formed in the right wall 18 as well as two mortises 38 formed integrally with the back wall 16 the blocks 10 can be arranged in a variety of patterns such as the pattern illustrated in fig3 for aesthetical reasons the bottom right corner block is exempted from having a mortise on its right hand wall a set of base blocks 40 are provided to seal off the blocks 10 of the lowermost row 43 of a given construction assembly each base block 40 has.