GLASGOW ARCHAEOLOGICAL SOCIETY.
north kerb at almost exactly the same height as does the protracted
line of the scarp at Bonnymuir, at a slope of 265 degrees. While
this example shows that the angle could be modified to some small
extent, the correlation of the fosse, vallum, and berm is made
more apparent. It is probable that, in the design, such a height
was given to the vallum as would prevent its being too readily
scaled. But once the height had been decided, the distance of
the vallum from the fosse was determined by the angle of the
scarp, the angle of repose. " If one could imagine," it has been
said by the exponent of this theory, " a vallum of the same
height and weight, brought to within a fourth of the present
distance from the fosse, it would be seen at once, from the great
mass above the protracted line of the scarp, how impossible it
would be to maintain that the fosse had been cut at the highest.
angle, or even approximately at the angle of repose."
Some of the positions in this argument have been questioned,
but the critics recognise its fruitfulness and value. They
admit at once that a steep rampart weighing about 1 cwt. per
cubic foot of its substance would exert a very great pressure on
the scarp if standing quite near it, and that therefore some
berm was necessary. They contend, however, that the slope of
the scarp (which, varying from 26 to 31 degrees, may be
conveniently considered as approximately a slope of J) was not
nearly so steep as the natural slope of earth,1 but, on the
contrary, was well within the angle of repose, so that a berm; not
of 23 feet but of 6 feet at the most, would have sufficed.
With the merits of this question we cannot attempt to deal.
All theorists alike have agreed in accepting the suggestion
of the theory under discussion as an integral and important
part of the explanation of the berm, and in thinking that
whatever may have been the primary causes and subsidiary
1 "The escarp ... is made as steep as the nature of the soil will allow, as
the steeper it is made the greater the obstacle it will be. Its slope in ordinary
ground is -J; sometimes it can be made steeper; but in weak soils, and when
works are required to last a considerable time, it will generally be impracticable
to give the escarp a steeper slope than \ unless it is artificially supported."
Philips, Article 127.
" The counterscarp . . . can be made steeper than the escarp, as it has not,
like the latter, to resist the pressure of the parapet. It is usually formed at
l\ I, or f" Philips, Article 130.