The more ancient boulder-clays of Scotland seem to have been formed when the land was undergoing a slow process of subsidence, or, as I should perhaps rather say, when a very considerable area of the earth's surface, including the sea-bottom, as well as the eminences that rose over it, was the subject of a gradual depression; for little or no alteration appears to have taken place at the time in the _relative_ levels of the higher and lower portions of the sinking area: the features of the land in the northern part of the kingdom, from the southern flanks of the Grampians to the Pentland Frith, seemed to have been fixed in nearly the existing forms many ages before, at the close, apparently, of the Oolitic period, and at a still earlier age in the Lammermuir district, to the south. And so the sea around our shores must have deepened in the ratio in which the hills sank. The evidence of this process of subsidence is of a character tolerably satisfactory. The dressed surfaces occur in Scotland, most certainly, as I have already stated on the authority of Dr. Fleming, at the height of fourteen hundred feet over the present sea-level; it has been even said, at fully twice that height, on the lofty flanks of Schehallion,--a statement, however, which I have had hitherto no opportunity of verifying. They may be found, too, equally well marked, under the existing high-water line; and it is obviously impossible that the dressing process could have been going on at the higher and lower levels at the same time. When the icebergs were grating along the more elevated rocks, the low-lying ones must have been buried under from three to seven hundred fathoms of water,--a depth from three to seven times greater, be it remembered, than that at which the most ponderous iceberg could possibly have grounded, or have in any degree affected the bottom. The dressing process, then, must have been a bit-and-bit process, carried on during either a period of elevation, in which the rising land was subjected, zone after zone, to the sweep of the armed ice from its higher levels _downwards_, or during a period of subsidence, in which it was subjected to the ice, zone after zone, from its lower levels _upwards_. And that it was the lower, not the higher levels, that were first dressed, appears evident from the circumstance, that though on these lower levels we find the rocks covered up by continuous beds of the boulder-clay, varying generally from twenty to a hundred feet in thickness, they are, notwithstanding, as completely dressed under the clay as on the heights above. Had it been a rising land that was subjected to the attrition of the icebergs, the debris and dressings of the higher rocks would have protected the lower from the attrition; and so the thick accumulation of boulder-clay which overlies the old coast line, for instance, would have rested, not on dressed, but on undressed surfaces. The barer rocks of the lower levels might of course exhibit