pavement on the surface of the
boulder-clay, and that generally bears atop a thin layer of sterile
soil, darkened by a russet covering of stunted heath. The binding cement
of the _pan_ is, as I have said, ferruginous, and seems to have been
derived from the vegetable covering above. Of all plants, the heaths are
found to contain most iron. Nor is it difficult to conceive how, in
comparatively flat tracts of heathy moor, where the surface water sinks
to the stiff subsoil, and on which one generation of plants after
another has been growing and decaying for many centuries, the minute
metallic particles, disengaged in the process of decomposition, and
carried down by the rains to the impermeable clay, should, by
accumulating there, bind the layer on which they rest, as is the nature
of ferruginous oxide, into a continuous stony crust. Wherever this _pan_
occurs, we find the superincumbent soil doomed to barrenness,--arid and
sun-baked during the summer and autumn months, and, from the same cause,
overcharged with moisture in winter and spring. My friend Mr. Swanson,
when schoolmaster of Nigg, found a large garden attached to the
school-house so inveterately sterile as to be scarce worth cultivation;
a thin stratum of mould rested on a hard impermeable pavement of _pan_,
through which not a single root could penetrate to the tenacious but not
unkindly subsoil below. He set himself to work in his leisure hours, and
bit by bit laid bare and broke up the pavement. The upper mould, long
divorced from the clay on which it had once rested, was again united to
it; the piece of ground began gradually to alter its character for the
better; and when I last passed the way, I found it, though in a state of
sad neglect, covered by a richer vegetation than it had ever borne under
the more careful management of my friend. This ferruginous pavement of
the boulder-clay may be deemed of interest to the geologist, as a
curious instance of deposition in a dense medium, and as illustrative
of the changes which may be effected on previously existing strata,
through the agency of an overlying vegetation.

I passed, on my way, through the ancient battle-field to which I have
incidentally referred in the story of the Miller of Resolis.[17] Modern
improvement has not yet marred it by the plough; and so it still bears
on its brown surface many a swelling tumulus and flat oblong mound,
and--where the high road of the district passes along its eastern