necessity of regarding as a consequence of miracle, a peculiarity of shape easily explicable on the principles of known law.

Now, the fact of a molten earth involves a long series of conditions, each different from all the others, and from the conditions of the present time. It involves the existence of a period in the history of our planet when life, animal or vegetable, was not, and of a succeeding period, when life began to be. It involves, too, the ripening of the earth from ages in which its surface was a thin, earthquake-shaken crust, subject to continual sinkings, and to fiery outbursts of the plutonic matter, to ages in which it is the very nature of its noblest inhabitant to calculate on its stability as the surest and most certain of all things. It involves, in short, those successive conditions of life in the geologic ages which, in connexion with what is now Scotland, I have, I am afraid, all too inadequately attempted to set before you in my present course. In fine, the primary rocks, when they underlie to a great thickness, as in our own country, the Paleozoic deposits, I regard as the deposits of a period in which the earth's crust had sufficiently cooled down to permit the existence of a sea, with the necessary denuding agencies, waves and currents, and, in consequence, of deposition also; but in which the internal heat acted so near the surface, that whatever was deposited came, as a matter of course, to be metamorphosed into semi-plutonic forms, that retained only the stratification. I dare not speak of the scenery of the period. We may imagine, however, a dark atmosphere of steam and vapour, which for age after age conceals the face of the sun, and through which the light of moon or star never penetrates; oceans of thermal water heated in a thousand centres to the boiling point; low half-molten islands, dim through the fog, and scarce more fixed than the waves themselves, that heave and tremble under the impulsions of the igneous agencies;

roaring geysers, that ever and anon throw up their intermittent jets of boiling fluid, vapour, and thick steam, from these tremulous lands; and, in the dim outskirts of the scene, the red gleam of fire, shot forth from yawning cracks and deep chasms, and that bears aloft fragments of molten rock and clouds of ashes. But should we continue to linger amid a scene so featureless and wild, or venture adown some yawning opening into the abyss beneath, where all is fiery and yet dark,—a solitary hell, without suffering or sin,—we would do well to commit ourselves to the guidance of a living poet of true faculty,-Thomas Aird,-and see with his eyes, and describe in his verse :—

'The awful walls of shadows round might dusky mountains seem,
But never holy light hath touched an outline with its gleam;
'Tis but the eye's bewildered sense that fain would rest on form,
And make night's thick blind presence to created shapes conform.
No stone is moved on mountain here by creeping creature cross'd,
No lonely harper comes to harp upon this fiery coast;
Here all is solemn idleness; no music here, no jars,
Where silence guards the coast ere thrill her everlasting bars;
No sun here shines on wanton isles; but o'er the burning sheet
A rim of restless halo shakes, which marks the internal heat;
As in the days of beauteous earth we see, with dazzled sight,
The red and setting sun o'erflow with rings of welling light.'

END OF THE LECTURES.

NOTE.

'The only shells I ever detected in the brick-clay of Scotland occurred in a deposit in the neighbourhood of St. Andrews, of apparently the same age as the beds at Portobello.'-Lecture Second, page 64.

NOTE. Some time after this statement was made, Mr. Miller devoted himself to a further investigation of the brick-clay beds in the neighbourhood of Portobello, and discovered several species of shells in situ, especially great abundance of Scrobicularia piperata, which he has described in a paper on the brick-clays, to be published hereafter. They form a very interesting portion of his Museum, now in the University of Edinburgh. 'But for him,' said an accomplished geologist, in talking with me on the subject, 'we would have known nothing whatever of the brickclays.'-L. M.

APPENDIX.

GANOID SCALES AND RAYS.

THE scales of the ganoid order consist of three plates,an inner, an outer, and an intervening one. The outer is composed mainly of enamel, and retains, when entire, however long exposed, much of the original dinginess of hue which it bore in the quarry: the inner is a plane of porcelanic-looking bone: the intermediate plate is finely composed of concentric lines, crossed from the centre to the circumference by finely radiating ones; and when, as mostly happens, this middle plate is exposed, the appearance of a mass of scales through the glass is of great beauty. The rays of our soft-finned fish (Malacopterygii), such as the haddock, seem as if cut through at minute distances, and then re-united, though less firmly than where the bone is entire, with the design, it would seem, of giving to the organs of motion which they compose the necessary flexibility, somewhat on the principle that a carpenter cuts halfthrough with his saw the piece of moulding which he intends bending along some rounded corner, or forcing into some concave. But in the ancient ganoid fish, in which the rays are bare enamelled bones, and necessarily of great rigidity, the joints appear real, not fictitious. We see them cut across into short lengths, a single fin consisting of many hundred pieces; and the problem lay in conceiving how