as rendering it
doubtful; the clay of which the interpolation is composed is found to
contain fragments, not only of the cornstone on which it rests, but also
of the Wealden limestone and shales which it underlies. It forms the
mere filling up of a flat-roofed cavern, or rather of two flat-roofed
caverns,--for the limestone roof dipped in the centre to the cornstone
floor,--which, previous to the times of the boulder-clay, had lain open
in what was then, as now, an old-world deposit, charged with long
extinct organisms, but which, during the iceberg period, was penetrated
and occupied by the clay, as run lime penetrates and occupies the
interstices of a dry-stone wall. It was no day for gathering fossils. I
saw a few ganoid scales, washed by the rain from the investing rubbish,
glittering on fragments of the limestone, with a few of the
characteristic shells of the deposit, chiefly Unionidae; but nothing
worth bringing away. The adhesive clay of the Weald, widely scattered
by the workmen, and wrought into mortar by the beating rains, made it a
matter of some difficulty for the struggling foot to retain the shoe,
and, sticking to my soles by pounds at a time, rendered me obnoxious to
the old English nickname of "rough-footed Scot." And so, after
traversing the heaps, somewhat like a fly in treacle, I had to yield to
the rain above and the mud beneath, and to return to do in Elgin what
cannot be done equally well in almost any other town of its size in
Scotland,--pursue my geological inquiries under cover.

On this, as on other occasions, I was struck by the complex and very
various forms assumed by the ganoid scales of the Wealden. Throughout
the Oolitic system generally, including the Lias, there obtains a
singular complexity of type in these little glittering tiles of
enamelled bone, which contrasts strongly with the greatly more simple
style which obtained among the ganoids of the Palaeozoic period. In many
of these last, as in the Coelacanth family, including the genera
Holoptychius, Asterolepis, and Glyptolepis, in all their many species,
with at least one genus of Dipterians, the genus Dipterus, the external
outline and arrangement of scale was as simple as in any of the Cycloid
family of the present time. Like slates on a roof, each single scale
covered two, and was covered by two in turn; and the only point of
difference which existed in relation to the _laying down_ of these massy
_slates_ of _bone_, and the lay