Essentially any wall where the stones in a layer are not more or less the same size can be said to be random. Most walls, even those built with relatively level bedded sandstones, are random built, however a general distinction can be made between those that are built out of flatter stone - simply random walls, and those built out of less regular stone - random rubble walls.
PHOTO A, Low Bradley, near Skipton, North Yorkshire c.60" including covers and copes, most stones under 2" thick>>
Joints are frequent in this style of wall although they can be avoided with care. Where this is achieved it tends towards a slightly less random face, mistaken by many for coursed walling. However the walls are not coursed as many of the adjacent stones are of differing heights, this is more obvious where larger and less regular stone is used. A wall where many of the stones are around 6" (15 cm) high with adjacent stones around an inch (25 mm) lower looks obviously random, where the stones are only around 1 ½" (38 mm) thick a difference in height between stones of only (6 mm) is proportionately the same, although nowhere near as obvious. Hence the wall is only well structured, rather than coursed. *****DIAGRAMS****
PHOTO B, near Ystradfellte, Powys. 55" including cover (excluding rubble)
Mc Afee ("Irish Stone Walls". The O`Brien Press, Dublin . 1997. p.44) provides a useful stylised diagram of this pattern which he describes as `random rubble uncoursed`
PHOTO C McAfee
Random Brought to Courses
Most well structured random walls are to some extent `random brought to courses`. True random brought to courses walls are brought to a level on two, three, or more occasions (depending on their height and stone size) as they are built up.
McAfee (p.42) again provides a useful stylised diagram.
<<PHOTO D McAfee>>
In practice duplication of this pattern is rare. Occasionally it can be found where the stonework is levelled along the length of the wall prior to the installation of through-stones, although many wallers shy away from it as a method unless the levelling stones are quite thick as it can lead to bands of thin stone within the face of the wall, although it is common in some areas with `slabby` flat sandstones
More normal practice is a rough levelling of the wall without using small stone in the smaller dips, instead placing a larger stone on them in effect breaking the coursing.
The end result can produce a well structured random face, which under close examination reveal some lines of levelling off, as in this example:
PHOTO E, Penisarwaun, Gwynedd, with tracing paper