e crabs and
periwinkles of the Frith of Forth are contemporary with the frogs and
lymnea of Flanders moss.

I had little time for exploration in the neighborhood of Elgin; but that
little, through the kindness of my friend Mr. Duff, I was enabled to
economize. We first visited together the outlier of the Weald at
Linksfield. It may be found rising in the landscape, a short mile below
the town, in the form of a green undulating hillock, half cut through by
a limestone quarry; and the section thus furnished is of great beauty.
The basis on which the hillock rests is formed of the well-marked
calcareous band in the Upper Old Red, known as the Cornstone, which we
find occurring here, as elsewhere, as a pale concretionary limestone of
considerable richness, though in some patches largely mixed with a green
argillaceous earth, and in others passing into a siliceous chert. Over
the pale-colored base, the section of the hillock is ribbed like an
onyx: for about forty feet, bands of gray, green, and blue clays
alternate with bands of cream-colored, light-green, and dark-blue
limestones; and over all there rests a band of the red boulder-clay,
capped by a thin layer of vegetable mould. It is a curious circumstance,
well fitted to impress on the geologist the necessity of cautious
induction, that the boulder-clay not only _overlies_, but also
_underlies_, this fresh-water deposit; a bed of unequivocally the same
origin and character with that at the top lying intercalated, as if
filling up two low flat vaults, between the upper surface of the
Cornstone and the lower band of the Weald. It would, however, be as
unsafe to infer that this intervening bed is older than the overlying
ones, as to infer that the rubbish which chokes up the vaulted dungeon
of an old castle is more ancient than the arch that stretches over it.
However introduced into the cavity which it occupies,--whether by
land-springs or otherwise,--we find it containing fragments of the green
and pale limestones that lie above, just as the rubbish of the castle
dungeon might be found to contain fragments of the castle itself. When
the bed of red boulder-clay was intercalated, the rocks of the overlying
Wealden were exactly the same sort of indurated substances that they are
now, and were yielding to the operations of some denuding agent. The
alternating clays and limestones of this outlier, each of which must
have been in turn an upper layer at the bottom of some lake o