According to the way in which the stone naturally lends itself, we have
various types of rubble walls. The commonest is the rough rubble wall
in which the stones have neither regular shapes nor regular sizes, or
even courses. The wall is composed of large stones and small stones
(the latter are called spalls, and fill in the interstices between
the larger stones). The joints of mortar between the stones may be
plastered roughly over the surface, covering much of the face of the
stones themselves, or they may be roughly but neatly pointed with
white mortar, or the joints may be raked out. Where the stone has a
natural tendency to cleave into long, flat shapes, the rough rubble may
become more regularly coursed in appearance. All of these types are
respectively illustrated in Figures 1, 2, 3, and 4.
[Illustration: Fig. 1. Rough Rubble—Plastered Joints