an angular form, with an interior angle in each covered. with small scales, and the rays, as in the case of the tail, forming but a fringe around it;- let him imagine the ventral fins, which lie far adown the body, of an exactly similar pattern, angular projections covered with scales in the centre, and fringed on two of their edges with rays; -exactly opposite to these, let there occur an anterior dorsal fin of comparatively small size, and then exactly opposite to the anal fin a posterior dorsal of at least twice the size of the other; let the anal fin be also large and sweeping, extending for a considerable way under the tail, which must like the tails of all the more ancient fish, be formed mainly on the under side, the vertebral column running on to its termination; and the fish so formed. will be a fair representation of the ancient Dipterus. Presenting externally in its original state no fragment of skin or membrane, and with even its most flexible organs sheathed in enamelled bone, it must have very much resembled a fish carved in ivory. What chiefly struck me in the examination was the peculiar structure of the ventral fins, the hind paws of the creature, if I may so speak. Their internal angle of scales imparts to them an appearance of very considerable strength, such an appearance as that presented by the hind fins of the Ichthyosaurus, which, as shown by a lately-discovered specimen, were furnished on the outer edges with a fringe of cartilaginous rays; and I deemed it interesting thus to mark the true fish approximating in structure, ere the reptilia yet existed, to the reptile type. The young frog, when in its transition state, gets its legs fully developed, and yet for some little time thereafter retains its tail. The Dipterus seems to have been a fish formed on this sort of transition plan.

FOSSIL-WOOD OF THE OOLITE AT HELMSDALE, SUTHERLAND.

What first strikes the observer in the appearance of the fossil-wood of this coast is the great distinctness with which the annual layers are marked. The harder lines of tissue, formed in the end of autumn, stand out as distinctly on the weathered surfaces as we see them in pieces of dressed deal that have been exposed for a series of years to the light and the air. The winters of the Oolitic period in this northern locality must have been sufficiently severe to have given a thorough check to vegetation. We are next struck by the great inequality of size in these layers, as we find them shown in separate specimens. I brought with me one specimen in which there is a single layer nearly half an inch in breadth, and another in which, in no greater space, there occur fourteen different layers. The tree to which the one belonged must have been increasing in bulk fourteen times more rapidly than that of the other. Occasionally, too, we find very considerable diversities of size in the layers of the same specimen. One year added to its bulk nearly half an inch; in another it increased scarce an eighth part. Then, as now, there must have been genial seasons, in which there luxuriated a rich-leaved vegetation, and other seasons of a severer cast, in which vegetation languished. My microscope, a botanist's, was of no great power; but by using its three glasses together, and carefully grinding down small patches of the weathered wood till it began to darken, I could ascertain with certainty, from the structure of the cellular tissue, what, indeed, seemed sufficiently apparent to the naked eye from the general appearance of the specimens, that they all belonged to the coniferæ. When viewed longitudinally, I could discern the elongated cells lying

side by side, and the medullary rays stretching at right angles across; but my glass lacked power to show the glandular dots. When viewed transversely the regularly reticulated texture of the coniferæ was very apparent. A bluish-gray limestone adhered to some of the specimens, and bore evidence in the same track. It abounded in cones and fragments of cones, in what seemed minute needle-shaped leaves, and in thin detached pieces of bark, like those which fall off in scales from the rind of so many of the coniferæ. The limestone bore also its frequent fragments of fern. There seemed nothing lacking to restore the picture. There rose before me a solemn forest of pines, deep, shaggy, and sombre; its opening slopes and withdrawing vistas were cheered by the lighter green of the bracken; and far beyond, where the coast terminated, and the feathery tree-tops were relieved against the dark blue of the sea, a long line of surf tumbled incessantly over a continuous reef of coral.

I picked up one very fine specimen, which, though it weighed nearly a hundred weight, I resolved on getting transported to Edinburgh, and which now lies on the floor before me. It is a transverse cut of a portion of a large tree, including the pith, and measures twenty-three inches across. In the sections of trees, figured by Mr. Witham in his interesting and valuable work, the original structure seems much disorganized: a granular radiating spar occupies the greater portion of the interior; and the tissue is found to exist in but detached portions. Here, on the contrary, the tissue exists unbroken from the pith to the outer ring. We may see one annual circle succeeding another in the average proportion of about ten per inch; and though we cannot reckon them continuously, for there are darker shades in which they disappear, shades

which the polisher of the marble-cutter may yet succeed in dissipating, the number of the whole must rather exceed than fall short of a hundred. However obscure the geologist may be in his eras generally, here at least is the record of one century. But how were its years filled? I sat beside the root of a newly-felled fir some six or eight seasons ago, and amused myself, when the severed vessels were throwing up their turpentine in minute transparent globules, in reckoning the years by the rings, from the bark inward. Here, I said, is the year in which the Reform Bill passed; and this the year in which Canning died; and this the year of the great commercial crisis; and this the year of Waterloo; and this of the burning of Moscow. The yearly rings of the Oolite have no such indices of recollection attached to them: we see their record in the marble, but know no more of contemporary history than that, when forests showed their fringes of lighter green on the hill-sides, and cell and fibre swelled under the rind, the promptings of instinct were busy all around and beneath,- that the pearly ammonite raised its tiny sails to the breeze, as the belemnite, with its many arms, shot past below,—that nameless birds mingled with flying reptiles, — and that, while the fierce crocodile watched in his pool for prey, the gigantic iguanodon stretched his long length of eighty feet in the sand. But who shall reveal the higher history of the time? The reign of war and of death had commenced long before; and who shall assert that moral evil had not long before cast its blighting shadows over the universe, that there had not been that war in heaven in which the uncreated angel had overthrown the dragon,—or that unhappy intelligences did not wander, "seeking rest, but finding none,' in an earth of "waste places," whose future sovereign still lay hid in the deep purposes of Eternity?

ASTREA OF THE OOLITE, SUTHERLAND.

The same deposit in which I found the wood embedded, contains large masses of coral, all apparently of one species, not a branching coral, but of the kind which consists of large stone-like masses covered on the surface with stellular impressions, framed in polygons, and which composes the genus Astrea. I picked up one very fine specimen, which I have since got cut through and polished. It presents a polygonal partitioning, of a delicate cream-color, that somewhat resembles the cells of a honeycomb. Each cell is filled with a brownish ground of carbonate of lime; and on this ground of brown there is a cream-colored star, composed of rays that proceed from the centre to the sides. One of these corals measured two feet and a half across in one direction, by two feet in another; and if it grew as slowly as some of its order in the present scene of things, its living existence must have stretched over a term of not less extent than that of its contemporary, the pine of the hundred rings. Some of the masses seem as if still adhering to the rocks on which they originally grew; the pentagonal cells are still open, as if the inhabitants died but yesterday; and the star-like lines inside still retain their original character of thin partitions, radiating outwards and upwards from a depressed centre. In other instances they have been torn from their places, and lie upturned in the shale, amid broken shells and fragments of wood. I brought with me one curious specimen perforated by an ancient pholas. The cavity exactly resembles those cavities of the existing Lithodomus shell which fretted so many of the calcareous masses that lay scattered on the beach on every side; but it is shut firmly up by the indurated shale in which the speci