We here close our review, over Scottish ground, of the earliest lessons to which we have access of the mineral structure of our globe. All the primary, palæozoic, and older class of the secondary rocks, are largely developed, leading us, indeed, a very little way into the inner chambers of the earth, but back through periods of time into the records of its history, for which the science itself furnishes no real standard of measurement. Vast, inconceivable cycles pass before the imagination, and fascinate the speculatist, while the sober inquirer pauses, doubts—nay, startles—at such remote undefined annals of creation. The legends and chronicles of Scotland are old indeed; but give geologists their own way, and what an antiquity would they assign to the mountains, valleys, and rivers of ancient Caledon! And yet, true it is, no rocks on the face of the earth can claim a deeper origin, an earlier arrangement, a more ancient ascent above the waters, than those whose nature and position we have so cursorily described. Leaving for the present the question as to Time, geology has this advantage, in facilitating an acquaintance with its principles, that its lessons are as general as they are particular. Go where you will the record is before you, so that, generally speaking, what is observed of its subject in one district or country, or even continent, has its counterpart in some other place near or remote. The rocks of Scotland are all on the great scale, not solitary and individual specimens, but wide-spread formations along the face of the country. With scarcely a single exception, every class of rocks described in our course stretches from sea to sea over the island. The structure of Scotland is peculiar in this, that the bearing and the strike of the various strata, are correspondent and continuous. Hence the parallelism of the great straths and valleys. The principal rivers are observant of the same law. The several formations, from the primary crystalline to the coal and upper sandstones, have a common axis of elevation from nearly E. N. E. to W. S. W., partaking more of an equatorial than of a meridional direction. The porphyries and chains of the older traps maintain a similar direction. The greenstones and basalts, polygonal and jointed, or otherwise, are for the most part to be found _within_ the area of the coal measures, or rising along the out-crop of the basins. Hence a description of any one locality will generally, in respect of the same series of rocks, be found applicable to another. The student may indifferently begin his researches as his convenience or sojourn for the time may direct. And whether it be the granite on the coasts of Aberdeen or of Arran—the schists of Glenisla or the Mull of Cantire—the silurian of St. Abb’s Head or Portpatrick—the devonian of Stonehaven or Girvan—the porphyries of Dundee or Largs—the shales and limestones of St. Andrews, Glasgow, or Ayr—the columnar