al lines by
which they are traversed at nearly right angles with their line of
stratification; the perpendicular front which they had covered comes to
be presented, in consequence, to the sea; its faults and cracks
gradually widen into caves, as those of the fallen front had gradually
widened at an earlier period; in the lapse of centuries, it too,
resigning its place, topples over headlong, an undermined mass; the
surge dashes white and furious where the dense rock had rested before;
and thus, in its slow but irresistible march, the sea gains upon the
land. In the peculiar disposition and character of the prevailing strata
of Orkney, as certainly as in the power of the tides which sweep athwart
its coasts, and the wide extent of sea which, stretching around it,
gives the waves scope to gather bulk and momentum, may be found the
secret of the extraordinary height to which the surf sometimes rises
against its walls of rock. During the fiercer tempests, masses of foam
shoot upwards against the precipices, like inverted cataracts, fully two
hundred feet over the ordinary tide-level, and, washing away the looser
soil from their summits, leaves in its place patches of slaty gravel,
resembling that of a common sea-beach. Rocks less perpendicular,
however great the violence of the wind and sea, would fail to project
upwards bodies of surf to a height so extraordinary. But the low angle
at which the strata lie, and the rectangularity maintained in relation
to their line of bed by the fissures which traverse them, give to the
Orkney precipices,--remarkable for their perpendicularity and their
mural aspect,--exactly the angle against which the waves, as broken
masses of foam, beat up to their greatest possible altitude. On a tract
of iron-bound coast that skirts the entrance of the Cromarty Frith I
have seen the surf rise, during violent gales from the north-west
especially, against one rectangular rock, known as the White Rock, fully
an hundred feet; while against scarcely any of the other precipices,
more sloping, though equally exposed, did it rise more than half that
height.

CHAPTER XIII.

Detached Fossils--Remains of the Pterichthys--Terminal Bones of the
Coccosteus, etc., preserved--Internal Skeleton of Coccosteus--The
shipwrecked Sailor in the Cave--Bishop Grahame--His Character, as
drawn by Baillie--His Successor--Ruins of the Bishop's
Country-house--Sub-aerial Formation of Sandstone--For