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CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority to U.S. Provisional Application No. 60/344,549, filed Oct. 18, 2001. 

   FIELD 
   The present invention relates to blocks, such as concrete blocks, for constructing walls, and more particularly to blocks employing a pin and slot system for interconnecting blocks stacked on top of each other in a wall. 
   BACKGROUND 
   Natural stone blocks cut from quarries have been used for a number of years to assemble walls of various types, including ornamental walls for landscaping purposes. Natural blocks have unique sizes, differences in shape and differences in appearance. However, construction of walls using such blocks requires significant skill to match, align, and place blocks so that the wall is erected with substantially uniform courses. While such walls provide an attractive ornamental appearance, the cost of quarried stone and the labor to assemble the stone blocks are generally cost prohibitive for most applications. 
   An attractive, low cost alternative to natural stone blocks are molded concrete blocks. In fact, there are several, perhaps hundreds, of utility and design patents which relate to molded blocks and/or retaining walls made from such blocks. Most prior art walls, however, are constructed from dimensionally identical blocks which can only be positioned in one orientation within the wall. Thus, a wall made from molded or cast blocks does not have the same random and natural appearance of a wall made from natural stone blocks. 
   Accordingly, there is a need for new and improved molded blocks and block systems and methods for constructing walls that have a more natural appearance than walls constructed using molded blocks, block systems, and molded block methods of the prior art. 
   SUMMARY 
   According to one embodiment, a block for constructing retaining walls comprises an upper surface spaced apart from a substantially parallel lower surface, opposed first and second faces, and opposed side surfaces extending between respective ends of the first and second faces, which together form a block body. A first pin-receiving recess is formed in the upper surface of the block. A first, longitudinally extending pin-receiving channel is formed in the lower surface of the block. The channel also intersects the side surfaces and extends continuously therebetween. 
   Desirably, the first face has a surface area greater than that of the second face. In a disclosed embodiment, the side surfaces taper inwardly from the first face to the second face. In another disclosed embodiment, only one of the side surfaces tapers inwardly from the first face to the second face and the other side surface is substantially perpendicular to the first and second faces. In both embodiments, the block is “reversible,” that is, either the first face or the second face can serve as the exposed face in one side of a wall, thereby giving the appearance that the wall is constructed from two differently sized blocks. 
   The pin-receiving recess in the upper surface may comprise either a pin hole or an elongate slot extending substantially parallel to the first and second faces. In either case, when constructing a wall, a pin may be inserted into the pin-receiving recess in the upper surface of the block. The exposed, upper portion of the pin can then be inserted into the pin-receiving channel in the lower surface of an overlying block. The channel permits a block to be shifted longitudinally in a course so that it is longitudinally offset from a block in an adjacent lower course. 
   The block also can be configured to permit placement of the block in a vertical orientation in a wall, as a jumper block. When used in this manner, the side surfaces serve as the upper and lower surfaces of the block in a wall and the upper and lower surfaces serve as the side surfaces of the block in a wall. Thus, a combination of both horizontally and vertically oriented blocks can be used to construct a wall. In blocks configured for use as a jumper, the first face of the block desirably has a length that is a multiple of the height of the block so that it is possible to achieve a level upper surface of the wall. 
   According to another embodiment, a block for constructing retaining walls comprises an upper surface spaced apart from a substantially parallel lower surface, opposed first and second faces, and opposed side surfaces extending between respective ends of the first and second faces. At least one pin-receiving aperture or pin hole is formed in the upper surface of the block. First and second longitudinally extending pin-receiving channels are formed in the lower surface. The channels extend at least partially between the side surfaces of the block. To interconnect a lower block with an overlying block in an adjacent upper course, the lower portion of a pin may be inserted into the pin-receiving aperture of the lower block the upper portion of the pin may be inserted in either of the first or second channels in the lower surface of the overlying block. 
   The block may further include first, second, third and fourth rows of pin holes in the upper surface. Each row extends longitudinally of the block and has at least one pin hole. The first and third rows of pin holes are spaced from the first and second faces, respectively, by a first distance. The second and fourth rows of pin holes are spaced from the first and second faces, respectively, by a second distance less than the first distance. The first and third rows of pin holes desirably are vertically aligned with the first and second channels, respectively, in the upper surface. In this manner, like blocks can be stacked directly over one another to form a vertical wall with a connecting pin being partially received in, for example, a pin hole of the first row of a lower block and the first channel of an overlying block. The pin and slot system also permits the interconnection of blocks stacked in a set forward or set backward manner. 
   In addition, the pin holes of the first row may be positioned so as to be tangent to or contacting a vertical plane defined by the first channel. Likewise, the pin holes of the third row may be positioned so as to be tangent to a vertical plane defined by the second channel. Thus, where an overlying block is stacked in vertically alignment with an adjacent lower block, the head of the connecting pin will abut a side surface in its respective channel in the overlying block to prevent retained earth from upsetting the vertical alignment of the blocks. 
   According to yet another embodiment, a block for constructing retaining walls comprises an upper surface spaced apart from a substantially parallel lower surface, opposed first and second faces, and opposed side surfaces extending between respective ends of the first and second faces. At least one pin hole is formed in the upper surface and at least one longitudinally extending trough is formed in the lower surface. The pin hole desirably is positioned tangent to a vertical plane defined by a side surface of the trough. 
   In another embodiment, a block system for constructing walls comprises a first and second set of blocks. The first set of blocks comprises a small, medium and large block, each of which has an upper surface spaced apart from a substantially parallel lower surface defining a block height, opposed first and second faces, and opposed side surfaces extending between respective ends of the first and second faces. The second set of blocks comprises a small, medium and large block, each of which has an upper surface spaced apart from a substantially parallel lower surface defining a block height, opposed first and second faces, and opposed side surfaces extending between respective ends of the first and second faces. 
   Within each set, the blocks have the same height and the same depth. In addition, the dimensions of the small, medium and large block of the first set desirably are equal to the dimensions of the small, medium and large block, respectively, of the second set, except that the blocks of the second set are greater in height than the blocks of the first set. In a disclosed embodiment, the height of the blocks of the second set is a multiple of the height of the blocks of the first set. 
   A method according to one embodiment of constructing a wall also is provided. The method includes providing a first block having a first face with a surface area greater than the surface area of an opposed second face. The first block is positioned in a first course with its lower surface facing the ground. A second block has a first face with a surface area greater than the surface area of an opposed second face. The second block is positioned in a second course on top of the first course in a vertical position so that a side surface of the second block is juxtaposed to the upper surface of the first block. 
   The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description of several embodiments, which proceeds with reference to the accompanying figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a bottom perspective view of a wall block according to one embodiment of my invention. 
       FIG. 2  is a top plan view of the block of  FIG. 1 . 
       FIG. 3  is a vertical sectional view of a wall, from front to back, constructed from like blocks having the configuration of the block of  FIGS. 1 and 2   
       FIG. 4  is a front elevational view of a wall constructed from like blocks having the configuration of the block of  FIGS. 1 and 2  wherein one such block is positioned in a vertical orientation as a jumper. 
       FIG. 5  is a vertical sectional view of the wall of  FIG. 4  taken along line  5 - 5  of  FIG. 4 . 
       FIG. 6  is a top plan view of a three-block system according to a second embodiment of my invention comprising a small, medium and large block. 
       FIGS. 7A-7G  are top plan views of various curvilinear walls that may be constructed from one or more of the sizes of blocks of the three-block system of  FIG. 6 . 
       FIG. 8  is a top plan view of a straight wall constructed from the three-block system of  FIG. 6 . 
       FIG. 9  is a top plan view of a corner block according to another embodiment of my invention for forming 90° corners. 
       FIG. 10  is a top plan view of a pilaster formed from four of the corner blocks of  FIG. 9 . 
       FIG. 11  is a top plan view of a rectangular wall enclosure constructed from the three-block system of  FIG. 6 . 
       FIGS. 12A-12C  illustrate, in top plan view, a block system comprising a first set of small, medium and large blocks of a first height and a second set of small, medium and large blocks of a second height. 
       FIG. 13  is a front elevational view of a wall constructed from various blocks of the block system depicted in  FIGS. 12A-12C . 
       FIG. 14  is a front elevational view of another wall constructed from various blocks of the block system depicted in  FIGS. 12A-12C , showing a large block of the first set and a large block of the second set being used as jumper blocks. 
       FIGS. 15A and 15B  are perspective views of the same block according to another embodiment of my invention, as viewed from above, showing one side surface and the bottom surface in  FIG. 15A , and the same side surface and the top surface in  FIG. 15B . 
       FIG. 16  is a bottom plan view of the block shown in  FIGS. 15A and 15B . 
       FIG. 17  is a bottom plan view of the bottom surface of a block according to another embodiment of my invention. 
       FIG. 18  is a vertical sectional view, from front to back, of a wall constructed from blocks all having the configuration of the block shown in  FIGS. 15A ,  15 B and  16 . 
       FIG. 19  is a front elevational view of a wall constructed from blocks all having the configuration of the block shown in  FIG. 16 . 
       FIG. 20  is a perspective view of a block according to another embodiment, as viewed from above, showing one side surface and the top surface. 
   

   DETAILED DESCRIPTION 
   In the following description, “upper” and “lower” refer to the placement of a block in a retaining wall. The lower, or bottom, surface of a block is placed such that it faces the ground. In a retaining wall, one row of blocks is laid down, forming a lowermost course or tier. An upper course or tier is formed on top of this lower course by positioning the lower surface of one block on the upper surface of another block. Additional course may be added until a desired height of the wall is achieved. Typically, earth is retained behind a retaining wall so that only a front surface of the wall is exposed. A free-standing wall (i.e., one which does not serve to retain earth) having two exposed surfaces may be referred to as a “fence.” 
   According to a first aspect, a block for constructing a wall is configured to be reversible, that is, the block has at least two surfaces of different dimensions, each of which can be used as the exposed face in a surface of a wall. According to another aspect, a pin and slot connection system for interconnecting blocks of adjacent courses permits alignment of blocks directly over one another, set forward, or set backward relative to one another so that either vertical or non-vertical walls may be constructed. 
   Referring first to  FIGS. 1 and 2 , there is shown a block  10  according to one representative embodiment.  FIG. 1  is a bottom perspective view of the block  10 , and  FIG. 2  is a top plan view of the block  10 . The block  10  comprises opposed side walls or side surfaces  12 , generally parallel bottom and top surfaces  14 ,  16 , respectively, and generally parallel first and second faces  18 ,  20 , respectively. The side walls  12  taper inwardly, or converge, as they extend from the first face  18  to the second face  20  so that acute angles  8  are formed between the first face  18  and side walls  12  and obtuse angles  6  are formed between the second face  20  and side walls  12 . Hence, the surface area of the first face  18  is greater than the surface area of the second face  20 . 
   Desirably, the surface texture of the first face  18  is the same as that for the second face  20 . In this manner, the block  10  is “reversible,” that is, either the first face  18  or the second face  20  can serve as the exposed face on one side of a wall. Since the first face  18  is larger than the second face  20 , a wall constructed from such blocks takes on a more random, natural appearance, than a wall in which the exposed faces of all blocks are equal in size. In the illustrated embodiment, for example, both the first face  18  and the second face  20  are provided with a roughened, split look (as shown in  FIG. 1 ) to contribute to the natural appearance of the wall. The block also may be “tumbled” to round the edges and corners of the block, as generally known in the art. Alternatively, the block  10  may be molded so that either of faces  18 ,  20  has a smooth, rather than a rough, surface. 
   Pin-receiving slots (also referred to herein as troughs or channels)  22 ,  24  formed in the bottom surface  14  extend longitudinally of the block between the side walls  12 , and preferably intersect the side walls as shown. The slots  22 ,  24  allow a block to be shifted longitudinally in a course either to the left or the right so that the block is longitudinally offset from a block in an adjacent lower course. Thus, a block in an upper course can be positioned to span two blocks in a lower course and be connected to them with a connected pin extending into one of the slots from one or both of the blocks in the lower course. Although less desirable, either of slots  22 ,  24  may extend only partially between the side walls  12 . For example, the length of the slots  22 ,  24  may be less than the distances between opposed side walls at the slots such that the slots do not intersect the side walls  12 . This configuration, however, limits the longitudinal placement of a block in an upper course relative to the blocks of a lower course. It would also eliminate the ability of a block to be stacked on its side in a wall, as shown in  FIG. 5 . 
   The block  10  may also have a centrally located core  28  between the channels  22 ,  24  to reduce the overall weight of the block  10 . The core  28  in the illustrated example is a semi-hollow or partial core that extends from the bottom surface  14  partially through the block  10 . The core  28  may be a full core, that is, a core that extends completely through the block  10 . When forming courses with blocks having full cores, the cores should be filled with a fill material, such as gravel, to prevent migration of earth into the core. In addition, the block  10  may have optional hand holds or handles  30  defined in the bottom surface  14  at each side wall  12  to facilitate carrying or placement of the block  10 . 
   The block  10  has a plurality of pin-receiving apertures such as pin holes  26   a - l  formed in the upper surface  16 . The pin holes  26   a - l  are shown as extending completely through the block, although this is not a requirement. In an alternative embodiment, the pin holes  26   a - l  extend partially through the block from the upper surface. In any event, the pin holes  26   a - l  are arranged in four rows extending substantially parallel to the first and second faces  18 ,  20 . 
   Each row in the illustrated embodiment has three such pin holes  26 , although the number of pins holes  26  in each row, as well as the number of rows of pin holes  26 , may vary. 
   As best shown in  FIG. 2 , pins holes  26   a ,  26   b  and  26   c  comprise an outer row  58  of pin holes which are vertically aligned with the channel  24 . Pin holes  26   j ,  26   k  and  26   l  comprise an outer row  60  of pin holes which are vertically aligned with the channel  22 . Desirably, pin holes  26   a ,  26   b ,  26   c  and  26   j ,  26   k ,  26   l  are positioned so as to have one side tangent to the inner wall of a respective channel  24 ,  22 . This, as explained in greater detail below, prevents earth retained behind the wall, which exerts forward pressure on the wall, from upsetting the vertical alignment of the blocks in the wall. The outer rows  58 ,  60  of pin holes are equally spaced a predetermined first distance from a longitudinal axis, or plane, L extending through the block halfway between the first and second faces  18 ,  20  that is, plane L bisects the block between its faces. Pin holes  26   d ,  26   e  and  26   f  comprise an inner row  62  of pin holes between the outer row  58  and the core  28 . Pin holes  26   g ,  26   h  and  26   i  comprise an inner row  64  of pin holes between the outer row  60  and the core  28 . The inner rows  62 ,  64  are equally spaced from the longitudinal axis or plane L a predetermined second distance that is less than the first distance. 
     FIG. 3  illustrates a vertical cross-sectional, side elevational view of a wall made from a plurality of blocks having the same general shape as block  10  shown in  FIGS. 1-2 . The wall has a front, exposed surface  54  and a second surface  56 , behind which earth may be retained. Of course, if the wall is a freestanding wall, then both the first and second surfaces  54 ,  56  are exposed. The first, lowermost course  36  of such a wall typically is laid in a trench (not shown) and successive courses  40 ,  44 ,  48  and  52  are laid one on top of the other. Either the first or second face  18 ,  20  of any one block may be used to form the front surface  54  of the wall. Pins  32  are used to hold the courses of blocks in place, although in some applications, such as where a wall is relatively short in height, the weight of the blocks may be sufficient to hold the blocks in place without the use of pins. The lower portion of such a pin  32  is received in any one of pin holes  26  in the upper surface  16  of a block. The upper portion, or head, of the pin  32  is positioned in one of the slots  22 ,  24  of an overlying block. 
   When constructing engineered or structural walls (e.g., walls typically built above a height of about four feet), a suitable geogrid can be placed between courses of blocks to extend into the hillside or earth behind the wall to give the wall sufficient strength and stability. Blocks having full cores (i.e., a core extending completely through the block) are preferred (although not required) when using geogrid because the fill material placed in the cores assists in retaining the geogrid between adjacent courses. 
   As mentioned, the pin and slot connection system permits vertical, set forward, or set back placement of blocks in a course relative to the blocks in an adjacent lower course. As shown in  FIG. 3 , the block  38  in the second course  36  is vertically aligned with the block  34  in the first, lowermost course  36 . The lower portion of a pin  32   a  in this illustration is positioned in a pin hole  26  of the outer row  58  of block  34 . The head of pin  32   a  is positioned in the slot  24  of block  38  so as to contact an inner surface of the slot  24 . This contact between the head of the pin and the inner surface of the slot resists any forward movement of block  38  caused by the pressure of earth retained behind the wall so as to maintain the desired vertical alignment of block  38  with respect to block  34 . To ensure that the wall is sufficiently stable, at least one pin is used to interconnect a block of one course with a block of an adjacent lower course (as shown in  FIG. 3 ), although more than one pin may be used for redundancy or for interconnecting a lower block with two overlying blocks. 
   Block  42  of the third course  44  is in a set back relation to block  38  of the second course  40 . In this position, slot  24  of block  42  is aligned over the inner row  62  of pin holes of block  38  with the lower portion of a pin  32   b  received in a pin hole  26  of block  38  and the head of pin  32   b  received in slot  24  of block  42 . Block  46  of the fourth course  48  is in a set forward relation to block  42  of the third course  44  with slot  24  of block  46  being aligned over an inner row  64  of pin holes  26  of block  42 . Block  46  is also reversed in the wall so that its second face  20  is exposed in the first surface  54  of the wall and its first face  18  is exposed in the second surface  56  of the wall. A pin  32   c  is partially received in a pin hole  26  of block  42  and slot  24  of block  46  to hold these blocks together. Block  50  of the fifth course  52  is in a set forward position with respect to block  46  of the fourth course  48 , with slot  22  of block  50  being aligned over an inner row  62  of pin holes  26  of block  46 . A pin  32   d  is partially received in a pin hole  26  in the upper surface  16  of block  46  and slot  22  of block  50 . 
   Referring again  FIGS. 1 and 2 , block  10  may be also configured to be placed in a vertical orientation in a wall, as a jumper block. When used in this way, the side walls  12  serve as the top and bottom of the block in a wall and the bottom surface  14  and the top surface  16  serve as the side walls of the block in a wall. The length of the first face  18  therefore is the effective height of the block when used as a jumper. 
   Because the side walls  12  are angled with respect to the first and second surfaces  18 ,  20 , the block  10 , when used as a jumper, would be tilted slightly from a vertical plane of the wall. Also, a block placed on top of the upwardly facing side wall  12  of the jumper would be supported at an angle. Thus, to support the jumper and any overlying block in a vertically upright position, pin-receiving slots  66  and  68  are formed in the side walls  12  proximate the ends of channel  22 . The widths w 1  of pin-receiving slots  66  and  68  are desirably, although not necessarily, dimensioned to form a frictional fit with the lower portion of a connecting pin  32 . When the block is turned on its side for vertical placement in a wall, pins are inserted into slots  66  and  68 , which then support the block and any overlying block in a vertically upright position. Pin-receiving slots  70  and  72  are similarly formed in the side walls  12  proximate the ends of channel  24 . Slot  70  serves as a pin hole for frictionally engaging the lower portion of a pin. Slot  72  has a width equal to that of channel  24  and serves as an extension of channel  24  to receive the upper portion of a pin. 
   Where a block is configured to be used as a jumper (such as shown in  FIGS. 1 and 2 ), the length of the first face  18  desirably evenly by, that is, a multiple of the height of the block. For example, if the length of the first face  18  is twice the height of the block, then a jumper will span two horizontally oriented blocks, or coarses, in the vertical direction. Thus, as explained below with respect to  FIG. 4 , it is still possible to achieve a level upper surface of the wall. 
     FIGS. 4 and 5  illustrate the use of block  10  as a jumper. A wall in this illustration includes a first block  74  of a first course, a second block  76  of a second course and a third block  78  of a third course. Blocks  74 ,  76  and  78  are of the same general shape as block  10  of  FIGS. 1 and 2 . The second block  76  is turned on its side so that one of its side walls  12  is adjacent the upper surface  16  of the first block  74  and the other is adjacent the lower surface  14  of the third block  78 . As shown in  FIG. 5 , the lower portion of a pin  75  is inserted into slot  68  of the second block  76  and the head of the pin  75  contacts the upper surface  16  of the first block  74  to support the downwardly facing side wall  12  of block  76  (i.e., the side wall  12  serving as the bottom of block  76 ) at a position above the upper surface  16  of block  74 . The exposed portion of the pin  75  (i.e., the portion extending from slot  68 ) is long enough to support the second block  76  in a vertically upright position. A pin  77  inserted into slot  66  of block  76  supports block  78  in a vertically upright position. Since pin  77  is aligned with channel  22  of block  78 , the upper portion of pin  77  should have a thickness or diameter greater than the width of channel  22  to prevent insertion of the pin therein. Alternatively, if pin  77  is a standard sized pin (i.e., a pin having a diameter that is less than the width of channel  22 ) a small section of pipe, having a diameter larger than the width of the channel  22 , can be placed over the upper portion of pin  77  to prevent insertion of pin  77  into channel  22  of block  78 . In an alternative embodiment, slot  66  is offset slightly from channel  22  of block  76  towards the first face  20  or second face  18  so that a pin inserted into slot  66  (such as pin  77  in  FIG. 5 ) is not vertically aligned with a channel in an overlying block. The lower portion of a pin  79  is received in a pin hole in the upper surface of block  74  and the upper portion of pin  79  is received in slot  72  of jumper block  76  to connect blocks  74  and  76 . The lower portion of a pin  81  is received in slot  70  of block  76  and the upper portion of pin  81  is received in a respective channel  24  in block  78  to connect blocks  76  and  78 . 
   As best shown in  FIG. 5 , a course may comprise blocks of different effective “heights,” thereby further contributing to the random appearance of the wall. In this illustration, the effective height of the jumper block  76  (i.e., the length of the first face  18 ) is equal to the overall height of two horizontally oriented blocks stacked on top of each other. Because the height of the jumper block  76  is a multiple of the height of the other blocks in the wall, it is possible to achieve a level upper surface of the wall. 
     FIG. 6  illustrates a block system of three differently sized blocks. The block system includes a first, small block  80 , a second, medium block  82  and a third, large block  84 . Each block is of the same general shape as the blocks disclosed in  FIGS. 1-5 . The large block  84  has a first face  86 , a second face  88  and converging side walls  90 . The medium block  82  has a first face  92 , a second face  94  and converging side walls  96 . The small block  80  has a first face  100 , a second face  98  and converging side walls  102 . The surface area of the first face of each block is larger than the surface area of its second face. Desirably, although not necessarily, each block is the same in depth (i.e, the distance from the first face to the second face of a block, for example, between the first face  86  and the second face  88  of the large block  84 ) and in height (i.e., the distance from the upper surface to the lower surface of a block). The length of the first face  86  of the large block  84  (i.e., the distance the first face  86  extends between side walls  90 ) desirably is equal to or a multiple of the height of the blocks so that it is possible to achieve a level top surface of a wall when the large block  84  is used as a jumper. 
   All three blocks may be formed in a single mold as a three-block module, such as shown in  FIG. 6 . A substantially v-shaped notch  104  defines a groove or split line for bisecting the large block  84  from the small and medium blocks,  80 ,  82 , respectively. These blocks may be split along notch  104  in any conventional manner, such as with a conventional hammer and chisel. Sacrificial portions (not shown) may be molded to faces  88 ,  94  and  100 , which are removed to provide the split look on those faces, as known in the art. During the casting process, a divider plate is positioned between small block  80  and medium block  82  at  106  to provide side wall  102  of block  80  and side wall  96  of block with a smooth surface. 
   The large block  84  is shown as having all of the features of block  10  shown in  FIGS. 1 and 2  and described above. The medium block  82  is similar to the large block  84 , except that it does not include the pin-receiving slots  66 ,  68 ,  70  and  72  of the large block  84 . The small block  80  is shown as having four rows of only one pin hole  26  in each row. The small block  80 , like the medium block  82 , also does not include the pin-receiving slots  66 ,  68 ,  70  and  72  of the large block  84 . Thus, in this particular system, only the large block  84  is used as a vertical jumper. However, in other systems, it is contemplated that either the small block or the medium block, or both, are configured to be used as a vertical jumper. 
   The block system can be used to construct various straight or curvilinear walls. As illustrated in  FIGS. 7A-7G , curved walls of various radii can be achieved with the block system.  FIG. 7A  shows a curved wall constructed from only small blocks  80 .  FIG. 7B  shows a curved wall constructed from only medium blocks  82 .  FIG. 7C  shows a curved wall constructed from only large blocks  84 .  FIG. 7D  shows a curved wall formed by alternating small blocks  80  and large blocks  84 .  FIG. 7E  shows a curved wall formed by alternating medium blocks  82  and large blocks  84 .  FIG. 7F  shows a curved wall formed by alternating small blocks  80  and medium blocks  82 .  FIG. 7G  shows a curved wall formed by repeating sequences of a small block  80 , a medium block  84  and a large block  86 . 
   The dimensions of the small, medium and large blocks may vary. In one specific embodiment of a three-block system, the first face  86  of the large block  84  is 16 inches in length and the second face  88  is 14 inches in length. The first and second faces  92 ,  94 , respectively, of the medium block  82  are 12 and 10 inches, respectively, in length. The first and second faces  100 ,  98 , respectively, of the small block  80  are 6 and 4 inches, respectively, in length. The depth of each block is 11.5 inches and the height of each block is 8 inches. The foregoing dimensions have been found to permit ease of handling and withstand the impact forces of the tumbling process. Of course, those skilled in the art will realize, these specific dimensions (as well as other dimensions provided in the present specification) are given to illustrate the invention and not to limit it. These dimensions can be modified as needed in different applications or situations. 
   The radii of the curved walls shown in  FIGS. 7A-7G , when constructed from small, medium and large blocks with the foregoing dimensions, are as follows: 36 inches for  FIG. 7A , 69 inches for  FIG. 7B , 94 inches for  FIG. 7C , 65 inches for  FIG. 7D , 80 inches for  FIG. 7E , 52 inches for  FIG. 7F , and 66 inches for  FIG. 7G . Of course, the radii of the walls will vary depending upon the dimensions of the blocks. For example, larger radius walls can be formed by increasing the lengths of the faces of the blocks. 
   The angles of convergence of the side walls of each block in the three-block system are substantially the same. Thus, placing blocks of any size side-by-side in a course, with every other block being reversed 180°, forms a substantially straight wall.  FIG. 8  illustrates a top plan view of one example of a wall formed by randomly placing small, medium and large blocks side-by-side with every other block being reversed so that the tapered side walls of each block is complemented by a side wall of an adjacent block to form a substantially straight wall. 
   Because the blocks of the three-block system have angled side walls, a corner block may be used to form a 90° corner at the end of a wall.  FIG. 9  illustrates one example of a corner block  108 . The corner block  108  includes a first face  110  and a second face  112 , which extend perpendicularly to each other to form a 90° corner. The first and second faces  110 ,  112 , respectively, typically are exposed faces, and as such, they may be provided with a roughened, or split, surface, to contribute to the natural appearance of the wall. A third face  114  is oriented at an obtuse angle  118  relative to the second face  112 . A fourth face  116  is oriented at an acute angle  120  relative to the first face  110 . Angles  118  and  120  of the corner block  108  are equal to the included angles  6  and  8 , respectively, of the small, medium and large blocks to complement the tapered side wall of an adjacent block in a course. The corner block  108  also includes pin holes  26  in the upper surface and a generally L-shaped channel  115  in the lower surface. 
     FIG. 10  shows a pilaster (i.e., a column) that can be formed from four corner blocks  108 . Such a pilaster can be used to reinforce or strengthen a wall and/or provide a more aesthetically pleasing wall. 
     FIG. 11  illustrates a top plan view of a rectangular enclosure constructed with the three-block system. Corner blocks  108  are positioned between the adjacent ends of the walls forming the enclosure. 
   Referring now to  FIG. 12A-C , there is shown a block system according to another embodiment comprising a first and second set of blocks. The first set of blocks comprises a small block  150 , a medium block  152  and a large block  154  and the second set of blocks comprises a small block  156 , a medium block  158  and a large block  160 .  FIG. 12A  illustrates a top plan view of both the large block  150  of the first set and the large block  156  of the second set.  FIG. 12B  illustrates a top plan view of both the medium block  152  of the first set and the medium block  158  of the second set.  FIG. 12C  illustrates a top plan view of the small block  154  of the first set and the small block  160  of the second set. 
   As shown in  FIGS. 12A-C , the small, medium and large block of each set has the same general shape as the small, medium and large block shown in  FIG. 6 . In addition, the dimensions of the small block  150 , medium block  152  and large block  154  of the first set are equal to the dimensions of the small block  156 , medium block  158  and large block  160 , respectively, of the second set, except that the blocks of the first set are greater in height than the blocks of the second set. Desirably, the height of the blocks of the first set is a multiple of the height of the blocks of the second set to permit the construction of a wall having a level or planar top surface. Within each set, the blocks have the same depth (i.e., the distance between the first face and the second face of a block) and height (i.e., the distance between the upper and lower surface of a block). 
   The large block  150  of the first set has a first face  124  and a second face  126 . The large block  156  of the second set has a first face  136  and a second face  138 . The length of the first face  124  of block  150  is equal to the length of the first face  136  of block  156 . The medium block  152  of the first set has a first face  128  and a second face  130 . The medium block  158  of the second set has a first face  140  and a second face  142 . The first faces  128 ,  140  of the medium blocks  152 ,  158  are equal in length. The small block  154  of the first set has a first face  132  and a second face  134 . The small block  160  of the second set has a first face  144  and a second face  146 . The first faces  132 ,  144  of the small blocks  154 ,  160  are equal in length. 
   As shown, the first face of each block is greater in surface area than the second face so that each block can be used to provide at least two differently sized faces in the surface of a wall. Thus, a wall constructed from the small, medium and large blocks of both sets has the appearance of a wall constructed from twelve differently sized blocks. The angles of convergence of the side walls of each block are the same so that blocks placed side-by-side with every other block being reversed with respect to an adjacent block forms a substantially straight wall. Significantly, any two adjacent blocks form a closed joint at the front and back surface of the wall so that there are no open spaces between blocks. Thus, a wall made of blocks of the present embodiment can be used as a free-standing wall or fence. 
     FIG. 13  illustrates one example of a wall constructed from small, medium and large blocks of each set. In this illustration, the height of the blocks of the first set (blocks  150 ,  152  and  154 ) is twice the height of the blocks of the second set (blocks  156 ,  158  and  160 ). Thus, as shown in  FIG. 13 , the courses of a wall may comprise blocks of different heights so as to contribute to the random, natural appearance of the wall and a level upper surface of the wall can be achieved by selective stacking of the blocks. This also can be accomplished with any two sets of blocks in which the height of the blocks of one set is a multiple of the height of the blocks of another set. For example, the height of the blocks of the first set can be three times the height of the blocks of the second set. 
   The wall of  FIG. 13  also includes blocks that are longitudinally offset with respect to blocks in an adjacent upper or lower course. For example, block  158   a  spans blocks  160   a  and  160   b  and part of block  160   c  in an adjacent lower course. Block  150   a  spans block  154   a  and block  154   b  and part of block  158   a  in an adjacent lower course and block  152   a  and part of block  152   b  in an adjacent upper course. Although not apparent in  FIG. 13 , the wall may include blocks that are vertically aligned over one another, set forward or set back. 
   In addition, any of the blocks of the first and second sets can be configured for use as a jumper block.  FIG. 14 , for example, shows both a large block  150   a  of the first set and large blocks  156   a  and  156   b  of the second set used as a jumper. The length of the first faces  124 ,  136  of blocks  150 ,  156 , respectively, desirably is equal to the overall height of several horizontally oriented blocks stacked on top of each other. In this illustration, the length of the first faces  124 ,  136  is equal to the height of two horizontally stacked blocks of the first set or four horizontally stacked blocks of the second set. 
   In a specific implementation of the present embodiment, the first set of blocks comprises a small, medium and large block having a height of 8 inches. The first and second faces  124 ,  126 , respectively, of the large block  150 , are 16 and 14 inches, respectively, in length. The first and second faces  128 ,  130 , respectively, of the medium block  152  are 12 and 10 inches, respectively, in length. The first and second faces  132 ,  134 , respectively, of the small block  154  are 6 and 4 inches, respectively, in length. The depth of each block of the first set is 11.5 inches. A second set of blocks comprises a small, medium and large block having the same dimensions except that the blocks of the second set have a height of 4 inches. 
   Referring now to  FIGS. 15A ,  15 B and  16  there is shown a block  200  according to another representative embodiment. As shown, block  200  includes generally parallel first and second faces  202 ,  204 , respectively, defining a block depth, and generally parallel top and bottom surfaces  206 ,  208 , respectively, defining a block height. Side walls  210  and  212  extend between respective ends of the first and second faces  202 ,  204 , respectively. Side wall  210  is perpendicular to the first face  202  and the second face  204 . Side wall  212  tapers inwardly from the first face  202  to the second face  204  so as to form an acute angle  214  with the first face  202  and an obtuse angle  216  with the second face  204 . Because of the tapered side wall  212 , the surface area of the first face  202  is greater than the surface area of the second face  204 . Both the first face  202  and the second face  204  may have a split or roughened surface. Block  200  is reversible so that either the first face  202  or the second face  204  can be positioned in a surface of a wall. 
   The top surface  206  includes longitudinally extending channels  218  and  220  extending substantially parallel to the first and second faces  202 ,  204 , respectively ( FIG. 15B ). Channels  218 ,  220  extend continuously between the side walls  210  and  212 , that is, channels  218 ,  220  extend completely across the block to intersect the opposite side walls. The bottom surface  208  of the block  200  includes longitudinally extending channels  222  and  224 , which also extend substantially parallel to the first face  202  and the second face  204  ( FIGS. 15A and 16 ). Channels  222  and  224  intersect the tapered side wall  212  but extend only partially across the block, terminating short of side wall  210 . 
   Channels  218  and  220  serve the purpose of pin receiving apertures, the same as pin holes  26  of block  10  in  FIGS. 1 and 2 . Thus, to interconnect blocks of adjacent courses, the lower portion of a pin  32  may be inserted into either of channels  218  or  220  in the top surface  206  of a lower block. Desirably, the widths of channels  218  and  220  are dimensioned to form a slight frictional fit with a pin  32 . The head of the pin is then received in either of slots  222  or  224  in the bottom surface  208  of an overlying block. 
   The sections of concrete between channels  222  and  224  and between channels  220  and  218  may be recessed slightly (e.g., about ⅛ inch) relative to the top and bottom surfaces to avoid damage to those sections when the block is tumbled. 
   Like block  10  of  FIGS. 1 and 2 , block  200  of the present embodiment permits alignment of blocks directly over one another, set forward, or set backward relative to one another so that either vertical or non-vertical walls may be constructed. Block  200  can also be turned on its side and used as a jumper. When used in this manner, the top and bottom surfaces serve as the side walls of the block in a wall and the side walls serve as either the top or bottom of the block in a wall. 
   In another embodiment, channels  218  and  220  are formed in the bottom surface of the block and channels  222  and  224  are formed in the top surface of the block. In yet another embodiment, a single channel is formed in each of the bottom and top surfaces. In the latter configuration, the channels desirably are equidistant from the first and second faces  202 ,  204  to permit the construction of vertical walls. 
     FIG. 17  illustrates a plan view of the bottom of a block  250  according to another embodiment. Block  250  is similar to block  200  of  FIGS. 15A ,  15 B and  16  in all respects except that block  250  has non-parallel first and second faces  252 ,  254 , respectively. The first face  252  is angled slightly so that it forms an acute angle  260  with side surface  256 . Similarly, the second face  254  is oriented to form an acute angle  262  with side surface  256 . Side surface  258  form an acute angle  264  with the first face  252  that is slightly less than angle  214  of block  200  and an obtuse angle  266  that is slightly greater than angle  216  of block  200 . 
   Block  250  is desirable in that angled first and second faces  202 ,  204 , respectively, provide for a substantially non-planar wall surface, thereby enhancing the natural appearance of the wall. 
     FIG. 18  shows a sectional, side elevational view of a wall constructed from a plurality of blocks which may have the same general shape of block  200  of  FIGS. 15A ,  15 B and  16  or block  250  of  FIG. 17 . Block  228  of the second course  238  is vertically aligned over block  226  of the first course  236 . A pin  246   a  is partially received in channel  220  of block  226  and channel  222  of block  228 . Although not shown in  FIG. 18 , block  228  may be shifted sideways in the second course  238  so as to span lower block  226  and another adjacent lower block in the first course  236 . Block  230  of the third course  240  is set back from block  228  of the second course  238 . A pin  246   b  is partially received in channel  220  of block  228  and channel  224  of block  230 . Block  232  of the fourth course  242  is turned as a jumper block, with the non-tapered side wall  210  serving as the bottom of the block and the tapered side wall  212  serving as the top of the block. A pin  246   c  is partially received in channel  218  of block  230  and the end of channel  218  of block  232 . To form a level, uppermost fifth course  244 , block  234  is stacked on top of block  232  with the tapered side wall  212  of block  234  supported on the tapered side wall  212  of block  232 . A pin  246   d  is partially received in channel  218  of block  232  and channel  220  of block  234  to interconnect blocks  232  and  234 . 
     FIG. 20  illustrates a perspective view of a block  270  according to another embodiment. Block  270  is similar to block  200  of  FIGS. 15A and 15B  in all respects except that block  270  has a single channel  272  formed in the top surface  206  and spaced equidistantly from the first and second faces  202 ,  204 . In addition, the spacing between channels  222  and  224  in the bottom surface  208  is greater in block  270  than in block  200  to minimize damage to the section of concrete between channels  222  and  224  if the block is tumbled. Block  270  can be positioned in a set forward or set backward relationship relative to a vertically adjacent block in a wall. 
     FIG. 19  shows a front elevational view of a wall constructed from a plurality of blocks  200 , although blocks having the same shape as block  250  of  FIG. 17  or block  270  of  FIG. 20  also may be used. As shown, block  200  may be positioned in either a horizontal orientation or a vertical orientation. Two blocks stacked in a vertical direction span a vertical distance equal to the total length of the first face  202  and the, second face  204 , which desirably is equal to the overall height of multiple blocks stacked in a horizontal orientation. In the present embodiment, for example, two blocks stacked in a vertical orientation span a vertical distance equal to the height of three horizontally stacked blocks. 
   The dimensions of block  200  may vary. In one specific embodiment, the depth of the block between the first and second face is about 8 inches. The height of the block between the upper and lower surfaces is 4.875 inches. The lengths of the first face and the second face are 8 inches and 6.5 inches, respectively. 
   The present invention has been shown in the described embodiments for illustrative purposes only. The present invention may be subject to many modifications and changes without departing from the spirit or essential characteristics thereof. We therefore claim as our invention all such modifications as come within the spirit and scope of the following claims.

Summary:
A wall block includes an upper surface spaced apart from a substantially parallel lower surface, opposed first and second faces, and opposed side surfaces converging between respective ends of the first and second faces. Blocks in a wall may be stacked on top of each other in either a vertical, set forward or set backward relationship. The length of a block face may be a multiple of its height, and the blocks otherwise are formed such that blocks may be stacked with the top surface of one block in abutment with a bottom surface of a vertically adjacent block or, optionally, with the top or bottom surface of one block in abutment with a side surface of a vertically adjacent block. The blocks may be manufactured in different sizes, such that their faces are of different lengths and heights, thereby enabling the construction of walls or fences of highly variable appearances.