You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF INVENTION 
     This invention relates to blocks and retaining walls suitable for gardens and other small non-construction sites. 
     BACKGROUND OF INVENTION 
     Small retaining walls for gardens and other sites of similar dimensions and requirements, are ideally constructed simply and with minimum equipment. 
     SUMMARY OF INVENTION 
     According to this invention, there is provided a block for forming a retaining wall comprising: (a) a body with front, rear, top, bottom and side surfaces and a central cavity with internal walls; (b) projecting means integrally formed on said bottom surface proximate said front surface and being laterally offset from said cavity and rearwardly offset from the front of the cavity and having a rounded front surface. 
     According to another aspect of this invention, there is provided a retaining wall comprising: (a) a lower row of blocks arranged side by side, each block having a body with a cavity and a rear surface; (b) an upper row of blocks arranged side by side, each block having a body with a cavity and projecting means integrally formed on said bottom surface, whereby said projecting means abut the rear surfaces of proximate block of the lower row. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     Advantages of the present invention will become apparent from the following detailed description taken in conjunction with preferred embodiments shown in the accompanying drawings, in which: 
     FIG. 1 is a plan view of a block according to the invention; 
     FIG. 2 is a side view of the block of FIG. 1; 
     FIG. 3 is a plan view of a second embodiment of the block of the invention; 
     FIG. 4 is a side view of the block of FIG. 3; 
     FIG. 5 is a perspective view of the block of FIGS. 1 and 2; 
     FIG. 6 is a perspective view of a wall formed of the block of FIG. 5; and 
     FIG. 7 is a perspective view of a variation of the wall of FIG. 6. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1, 2 and 5 show a first embodiment of a block 2 for forming a retaining wall. Block 2 includes spaced front and rear wall portions 4 and 6 respectively. A pair of side walls 8 extend between and join the front and rear wall portions to define a central open cavity 10 through the block having internal side walls 11, internal front wall 13 and internal rear wall 17. The block has upper surface 12 and a lower surface 14. Block 2 is preferably formed from concrete and the face of front wall portion 4 is formed with a roughened pattern 16. Block 2 has a generally trapezoidal shape in plan view with the wall portion 4 wider than the rear wall portion 6. 
     Rear wall portion 6 of block 2 includes a frangible extension 28 that extends beyond sidewalls 8. Extensions 28 can be broken off along pre-formed fault lines 29 (e.g. by a hammer) so that block 2 is reduced to essentially an arcuate segment. Such a block 2 can then be rotated to a desired angle to form a curved retaining wall, as shown in FIG. 7 described below. 
     Block 2 is provided with projecting means in the form of a pair of spaced, cylindrical extensions or knobs 18. Knobs 18 are integrally formed on the lower surface 14 of side walls 8 behind the front edge of cavity 18. Although knob 18 is shown to be cylindrical, it need only have a front curved surface to be able to rotate and accommodate a desired curved configuration of retaining wall, or could have a flat front surface if non-curved configurations are sufficient. Although knob 18 is shown to be positioned proximate the front edge of cavity 18, knob 18 can be positioned farther rearwardly. The extent that knob 18 is positioned behind the front edge of cavity 18 determines the rearward offset of the wall constructed, as described below. 
     FIGS. 6 and 7 show retaining walls constructed with the foregoing described first embodiment of blocks 2. A first row of blocks 2 is laid on the ground or in a shallow trench dug in the ground. Blocks 2 are backfilled with soil 99 and cavities 10 are filled with soil or loose angular gravel and dirt, to anchor the row of blocks 2, to permit drainage of water therethrough, and to permit plants and flowers to be planted therein. After completion of the first row and backfilling as described, a second row of blocks 2 is laid. The blocks 2 of the second row are laterally offset from the blocks 2 of the first row. In particular, a block 2 of the second row is positioned in approximately half bond relationship to two underjacent blocks 2 of the first row (i.e. the upper block 2 is centered approximately at the plane of contact between the two underjacent blocks 2. The two knobs 18 of a block 2 of the second row abut the respective rear wall portions 6 of the two adjacent blocks 2 of the first row. One such abutment of knob 18 is shown in FIG. 6. Thus formed, the second row of blocks 2 are rearwardly offset from the first row of blocks 2. Then the blocks 2 of the second row are backfilled and filled, and the above process is continued for perhaps several more rows for a common garden setting. 
     FIG. 7 shows an arcuate wall of blocks 2 where the frangible extensions 28 have been removed. 
     FIGS. 3 and 4 show a second embodiment of block 2 having generally larger dimensions than those of the first embodiment. A reinforcing web 15 is provided between side walls 8 at substantially mid-length therealong to form front and rear internal cavities 10 and 10a. The blocks of FIGS. 3 and 4 are used for larger retaining walls because their additional size and mass allows them to support a greater bulk of soil. The method of creating retaining walls described above for the first embodiment of block 2, is applied to the second embodiment of block 2. One variation (not shown) is that knobs 18 may abut the rear wall portion 6 or be inserted into rear internal cavity 10a and abut a front surface thereof, thus allowing a variation in the rearwardly offset of superjacent rows of blocks 2. In contrast, a wall employing the first embodiment of block 2 will have a uniform rearwardly offset between superjacent rows. 
     Typical dimensions of the fist embodiment of block 2 are 4&#34; high by 12&#34; wide by 8&#34; deep with knobs 0.5&#34; high and 2.5&#34; in diameter if the knob is cylindrical. It will be appreciated that the dimensions given are merely for purposes of illustration and are not limiting in any way. The specific dimensions given may be varied in practising this invention, depending on the specific application. 
     While the principles of the invention have now been made clear in the illustrated embodiments, there will be immediately obvious to those skilled in the art, many modifications of structure, arrangements, proportions, the elements, materials and components used in the practice of the invention, and otherwise, which are particularly adapted for specific environments and operational requirements without departing from those principles. The claims are therefore intended to cover and embrace such modifications within the limits only of the true spirit and scope of the invention.

Summary:
A block useful for constructing retaining walls for gardens, has two bottom lugs or knobs, bracketing an internal cavity. The cavity may be filled with soil. In forming a wall, the upper row of blocks is rearwardly onset from the lower row of blocks, whereby the lugs of the blocks of the upper row abutting the back surfaces of the blocks of the lower row.