ials. Considerable beds of shingle, brought down by the North
Esk, are seen along the beach.

Proceeding southwards, we learn that at Arbroath, in Forfarshire, which
stands on a rock of red sandstone, gardens and houses have been carried
away since the commencement of the present century by encroachments of
the sea. It had become necessary before 1828, to remove the lighthouses
at the mouth of the estuary of the Tay, in the same county, at Button
Ness, which were built on a tract of blown sand, the sea having
encroached for three-quarters of a mile.

_Force of waves and currents in estuaries._--The combined power which
waves and currents can exert in _estuaries_ (a term which I confine to
bays entered both by rivers and the tides of the sea), was remarkably
exhibited during the building of the Bell Rock Lighthouse, off the mouth
of the Tay. The Bell Rock is a sunken reef, consisting of red sandstone,
being from twelve to sixteen feet under the surface at high water, and
about twelve miles from the mainland. At the distance of 100 yards,
there is a depth, in all directions of two or three fathoms at low
water. In 1807, during the erection of the lighthouse, six large blocks
of granite, which had been landed on the reef, were removed by the force
of the sea, and thrown over a rising ledge to the distance of twelve or
fifteen paces; and an anchor, weighing about 22 cwt., was thrown up upon
the rock.[395] Mr. Stevenson informs us moreover, that drift stones,
measuring upwards of thirty cubic feet, or more than two tons' weight,
have, during storms, been often thrown upon the rock from the deep
water.[396]

_Submarine forests._--Among the proofs that the sea has encroached on
the land bordering the estuary of the Tay, Dr. Fleming has mentioned a
submarine forest which has been traced for several miles along the
northern shore of the county of Fife.[397] But subsequent surveys seem
to have shown that the bed of peat containing tree-roots, leaves, and
branches, now occurring at a lower level than the Tay, must have come
into its present position by a general sinking of the ground on which
the forest grew. The peat-bed alluded to is not confined, says Mr.
Buist, to the present channel of the Tay, but extends far beyond it, and
is covered by stratified clay from fifteen to twenty-five feet in
thickness, in the midst of which, in some places, is a bed full of
sea-shells.[398] Recent discoveries having established the fact that