the country, comes to exhibit
its completely vitrified fort where there had been but a loosely-piled
hill-fort before. It in no degree militates against this compound
theory,--borrowed in part from Williams and in part from Sir
George,--that there are detached vitrified masses to be found on
eminences evidently never occupied by hill-forts; or that there are
hill-forts on other eminences only partially fused, or hill-forts on
many of the less commanding sites that bear about them no marks of fire
at all. Nothing can be more probable than that in the first class of
cases we have eminences that had been selected as beacon-stations, which
had not previously been occupied by hill-forts; and in the last,
eminences that had been occupied by hill-forts which, from their want of
prominence in the general landscape, had not been selected as
beacon-stations. And in the intermediate class of cases we have probably
ramparts that were only partially vitrified, because some want of fuel
in the neighborhood had starved the customary fires, or because fires
had to be less frequently kindled upon them than on the more important
stations; or, finally, because these hill-forts, from some disadvantage
of situation, were no longer used as places of strength, and so the
beacon-keepers had no motive to attempt consolidating them throughout by
the piecemeal application of the vitrifying agent. But the old Highland
mode of accounting for the present appearance of Knock Farril and its
vitrified remains is perhaps, after all, quite as good in its way as any
of the modes suggested by the philosophers.[20]

I spent some time, agreeably enough, beside the rude rampart of Knock
Farril, in marking the various appearances exhibited by the fused and
semi-fused materials of which it is composed,--the granites, gneisses,
mica-schists, hornblendes, clay-slates, and red sandstones of the
locality. One piece of rock, containing much lime, I found resolved into
a yellow opaque substance, not unlike the coarse earthenware used in the
making of ginger-beer bottles; but though it had been so completely
molten that it had dropped into a hollow beneath in long viscid trails,
it did not contain a single air-vesicle; while another specimen,
apparently a piece of fused mica-schist, was so filled with air-cells,
that the dividing partitions were scarcely the tenth of a line in
thickness. I found bits of schistose gneiss resolved into green glass;
the Old Red Sandstone