-line. On this
flat terrace most of the seaport towns of the empire are built. The
subsoil which underlies its covering of vegetable mould consists usually
of stratified sands and gravels, arranged after the same fashion as on
the neighboring beach, and interspersed in the same manner with sea
shells. The escarpment behind, when formed of materials of no great
coherency, such as gravel or clay, exists as a sloping, grass-covered
bank,--at one place running out into promontories that encroach upon the
terrace beneath,--at another receding into picturesque, bay-like
recesses; and where composed, as in many localities, of rock of an
enduring quality, we find it worn, as if by the action of the surf,--in
some parts relieved into insulated stacks, in others hollowed into deep
caverns,--in short, presenting all the appearance of a precipitous
coast-line, subjected to the action of the waves. Now, no geologist can
or does doubt that this escarpment was at one time the coast-line of the
island,--the line against which the waves broke at high water in some
distant age, when either the sea stood from twenty to thirty feet higher
along our shores than it does now, or the land sat from twenty to thirty
feet lower. Nor can the geologist doubt, that along the flat terrace
beneath, with its stratified beds of sand and gravel, and its
accumulations of sea shells, the tides must have risen and fallen twice
every day, as they now rise and fall along the beach that at present
girdles our country. But, in reference to at least human history, the
age of the old coast-line and terrace must be a very remote one. Though
geologically recent, it lies far beyond the reach of any written record.
It has been shown by Mr. Smith of Jordanhill, one of our highest
authorities on the subject, that the wall of Antoninus, erected by the
Romans as a protection against the Northern Caledonians, was made to
terminate at the Firths of Forth and Clyde, with relation, not to the
level of the old coast-line, but to that of the existing one. And so we
must infer that, ere the year A.D. 140 (the year during which, according
to our antiquaries, the greater part of the wall was erected) the old
coast-line had attained to its present elevation over the sea. Further,
however, we know from the history of Diodorus the Sicilian, that at a
period earlier by at least two hundred years, St. Michael's Mount, in
Cornwall, was connected with the mainland at low water, just as it