informed by Mr. William Watt, a competent authority in the case,
that the arrangement is comparatively a common one in the quarries of
Orkney. How account for the phenomenon? How account for the three
storeys, and the apportionment of the floors, like those of a great
city, each to its own specific class of society? Why should the first
floor be occupied by Osteolepides, the second by Cheiracanthi and their
congeners, and the third by Coccostei? Was the arrangement an effect of
normal differences in the constitutions of the several families,
operated upon by some deleterious gas or mineral poison, which, though
it eventually destroyed the whole, did not so simultaneously, but
consecutively,--the families of weakest constitution first, and the
strongest last? Or were they exterminated by some disease, that seized
upon the families, not at once, but in succession? Or did they visit the
locality serially, as the haddock now visits our coasts in spring, and
the herring towards the close of summer; and were then killed off,
whether by poison or disease, as they came? These are questions which
may never be conclusively answered. It is well, however, to observe, as
a curious geological fact, that peculiar arrangement of the fossils by
which they are suggested, and to record the various instances in which
it occurs. The minerals which I remarked among the schists here as most
abundant are a kind of black ironstone, exceedingly tough and hard,
occurring in detached masses, and a variety of bright pyrites
disseminated among the darker flagstones, either as irregularly-formed,
brassy-looking concretions of small size, or spread out on their
surfaces in thin leaf-like films, that resemble, in some of the
specimens, the icy-foliage with which a severe frost encrusts a
window-pane. Still further on I came upon a vein of galena; but a
miner's excavation in the solid rock, a little above high-water mark,
quite as dark and nearly as narrow as a fox-earth, showed me that it had
been known long before, and, as the workings seemed to have been
deserted for ages, known to but little purpose. The crystals of ore,
small and thinly scattered, are embedded in a matrix of barytes,
stromnite, and other kindred minerals, and the thickness of the entire
vein is not very considerable. I have since learned, from the
"Statistical Account of the Parish of Sandwick," that the workings of
the mine penetrate into the rock for about a hundred yards, but that