GLASGOW ARCHAEOLOGICAL SOCIETY.
ments most frequently recurrent over all are a quarter-inch
and a half-inch. The shades of colour vary considerably also;
at some points they are black and bold ; at others they are not
black, but merely dark; at others again they are so faint and thin
as to be hard to detect. Striking an average over the whole of
the sections, it may be said that the distance between these
strange lines is usually about three inches, and their general
colour a mossy brown. But wider or closer, darker or lighter,
thicker or thinner, there the lines are, not in one section,
but in them all.
These appearances are just such as a great sod wall might be
expected to yield. Indeed, the facts of a special section made
through an undoubted old sod dyke1 are astonishingly like those
of the sections at Bonnyside. The singular variations in the
thickness of the black line at various points along the vallum
would be amply accounted for by the differences in the soils
from which the sods were taken at these various points. Any-
thing like uniformity in the character of the sods employed
would be almost out of the question. But all such hypothetical
considerations must be tested by the practical question of the
actual consistency of these dark lines. If they are vegetation
marks they must contain a large admixture of vegetable matter.
This test they fully sustain, for by the kind services of Mr.
George Paterson, analytical chemist, Liverpool, it has been
demonstrated that a varying proportion, averaging about 14
per cent., of the substance of these dark lines is vegetable
Whether wood in the form of branches or fascines—the
cervoli of Hyginus—entered in any degree into the composition
of the vallum, and consequently into the formation of these dark
lines, is a question possibly admitting of further examination.
In itself the supposition appears highly probable, although the
indications are rather negative. At one place indubitable charred
1 Notes of a section made in sod dyke over 100 years old on farm of Horseclose,
Ruthwell, Dumfriesshire :—
Bottom of white sand ; on ground level a dark line ; next 2 inches of white
sand; then a black line 1 inch thick; white sand again for 4 inches ; black
line, 1 inch; white sand 3 inches; black line 1 inch; white sand 3 inches ;
black sod surface, grass-grown, 4 inches, forming top of section.