A finite unit of sand (or sandstone) that usually accumulated in response to one type of depositional process (e.g. as a channel, beach-bar, or barrier system). The distribution of the sand and the three-dimensional geometry (architecture) is controlled largely by the nature of the depositional regime under which it accumulated (i.e. channel sands may be sinuous, and beach or shore-bar sands may be linear and shore-parallel, etc.).