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 is now, by a flat isthmus, across which, upon the falling of the tide, the ancient Cornish miners used to carry over their tin in carts. Had the relative levels of sea and land been those of the old coast-line at the time, St. Michael's Mount, instead of being accessible at low ebb would have been separated from the shore by a strait from three to five fathoms in depth. It would not have been then as now, as described in the verse of Carew,-- "Both land and island twice a day." But even the incidental notice of Diodorus Siculus represents very inadequately the antiquity of the existing coast-line. Some of its caves, hollowed in hard rock in the line of faults and shifts by the attrition of the surf, are more than a hundred feet in depth; and it must have required many centuries to excavate tough trap or rigid gneiss to a depth so considerable, by a process so slow. And yet, however long the sea may have stood against the present coast-line, it must have stood for a considerably longer period against the ancient one. The latter presents generally marks of greater attrition than the modern line, and its wave-hollowed caves are of a depth considerably more profound. In determining, on an extensive tract of coast, the average profundity of both classes of caverns from a considerable number of each, I ascertained that the proportional average depth of the modern to the ancient is as two to three. For every two centuries, then, during which the waves have been scooping out the caves of the present coast-line, they must have been engaged for three centuries in scooping out those of the old one. But we know _historically_, that for at least twenty centuries the sea has been toiling in these modern caves; and who shall dare affirm that it has not been toiling in them for at least ten centuries more? But if the sea has stood for but even two thousand six hundred years against the present coast-line (and no geologist would dare fix his estimate lower), then must it have stood against the old line, ere it could have excavated caves one third deeper, three thousand nine hundred years. And both periods united (six thousand five hundred years) more than exhaust the Hebrew chronology. Yet what a mere