of Thurso.
Calcareo-bituminous flags, grits, and shales, of which the paving
flagstones of Caithness may be regarded as the general type, occur on
the shores, in reefs, crags, and precipices; here stretching along the
coast in the form of flat, uneven bulwarks: there rising over it in
steep walls; yonder leaning to the surf, stratum against stratum, like
flights of stairs thrown down from their slant position to the level; in
some places severed by faults; in others cast about in every possible
direction, as if broken and contorted by a thousand antagonist
movements; but in their general bearing rising towards the east, until
the whole calcareo-bituminous schists of which this important member of
the system is composed disappear under the red sandstones of Dunnet
Head. Such, in effect, is the general description of Mr. Sedgwick and
Sir R. Murchison, of the rocks in the neighborhood of Thurso. It
indicates further, that in at least three localities in the range there
occur in the grits and shales, scales and impressions of fish. And such
was the ascertained geology of the deposit when taken up last year by an
ingenious tradesman of Thurso, Mr. Robert Dick, whose patient
explorations, concentrated mainly on the fossil remains of this deposit,
bid fair to add to our knowledge of the ichthyology of the Old Red
Sandstone. Let us accompany Mr. Dick in one of his exploratory rambles.
The various organisms which he disinterred I shall describe from
specimens before me, which I owe to his kindness,--the localities in
which he found them, from a minute and interesting description, for
which I am indebted to his pen.

Leaving behind us the town at the bottom of its deep bay, we set out to
explore a bluff-headed parallelogramical promontory, bounded by Thurso
Bay on the one hand, and Murkle Bay on the other, and which presents to
the open sea, in the space that stretches between, an undulating line of
iron-bound coast, exposed to the roll of the northern ocean. We pass two
stations in which the hard Caithness flagstones so well known in
commerce are jointed by saws wrought by machinery. As is common in the
Old Red Sandstone, in which scarce any stratum solid enough to be of
value to the workmen, whether for building or paving, contains good
specimens, we find but little to detain us in the dark coherent beds
from which the flags are quarried. Here and there a few glittering
scales occur; here and there a few coprolitic patches; her