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such a fin was to be wrought,—whether, for instance, each detached length was to have its moving ligament; and if so, how a piece of machinery so very complicated and multifarious was to be set and kept in motion. Here, however, I found the problem very simply resolved. The rays of the ganoid fish, like its scales, consist of three plates,two plates of enamel, one on each side, and an interior plate of bone. Now the joints,—though so well marked, that in rays imbricated on the sides, as in those of the Cheirolepis, the imbricated markings turn the corners, if one may so speak, just as the carvings on a moulding recounter, as a workman would say, at the corners of a building, -are not real joints after all : they reach but through the inflexible enamel, leaving the central plate of bone undivided. Like the rays of the Malacopterygii, they are formed on the principle of the half-sawn moulding. I observed, too, that the inner plate is in every instance considerably narrower than the plates of enamel which rest upon it. In the lateral edges of every ray which composes the inner portion of the fin there must exist a groove, therefore; and in this groove, it is probable, the connecting membrane at one time lay hid, performing, like an invisible hinge, its work unseen.
RECENT BONE-BED IN THE FORMING.
I ONCE found an interesting illustration of the bone-bed, coupled with at least one of the causes to which it owes its origin, in the upper part of the Moray Firth. I had been spending a night at the herring-fishing, on one of the most famous fishing-banks of the east coast of Scotland,—the bank of Guilliam. It is a long, flat ridge of rock that rises to within ten or twelve fathoms of the surface. On its southern edge there is a submarine valley that sinks to at least twice that depth; and in the course of the night our boat drifted from off the rocky ridge, the haunt of the herrings, to the deepest part of the valley, where scarce a herring is ever found. Our nets had, however, brought fish with them from the fishing-ground, sufficient in quantity to sink them to the bottom of the hollow; and in raising them up,—a work of some little exertion,—we found them bedaubed with patches of a stinking, adhesive mud, that, where partially washed on the surface, seemed literally bristling over with minute fish-bones. The muddy bottom of the valley may be regarded as a sort of submarine burialground,-an extensive bone-bed in the forming. "What,' we asked an intelligent old fisherman, 'brings the fish here to die? Have you observed bones here before ?' 'I have observed them often,' he said: 'we catch few herrings here; but in winter and spring, when the cold draws the fish from off the shallows into deep water, we catch a great many haddocks and cod in it, and bring up on our lines large lumps of the foul bottom. In spring, when most of the small fish are sickly and out of season, and too weak to lie near the shore, where the water is rough and cold, they take shelter in the deep here in shoals; and thousands of them, as the bones testify, die in the mud, not because they come to die in it, but just because their sickly season is also their dying season. And such seemed to be the true secret of the accumulation. The fish resorted to this place of shelter, not in order that they might die, but that they might live ; just as people go to poor-houses and hospitals with a similar intention, and yet die in them at times notwithstanding. And hence, I doubt not, in most instances those accumulations of fish-bones which men accustomed to the use of the trawl-net find in detached spots of bottom, when in other parts, not less frequented by fish in the milder seasons, not a single bone is to be found, and which have been described as dying places. The dying places,-the deep burial-grounds of the sea's finny inhabitants,-will be found almost always to prove their places of shelter. And hence, it is probable, many of the bone-beds of the geologist.
DIPTERUS MACROLEPIDOTUS ABUNDANT IN THE BANNISKIRK
OLD RED OF CAITHNESS.
LET the reader imagine a fish delicately carved in ivory, and then crusted with a smooth shining enamel, not less hard than that which covers the human teeth, but thickly dotted with minute puncturings, as if stippled all over with the point of a fine needle ;- let him imagine the enamelled rays lying so thickly in the fins, that no connecting membrane appears, and that each individual ray consists of numerous pseudo-joints, so rounded at their terminations, that each joint seems a small oblong scale, or each ray, rather, a string of oval beads ;-in due harmony with the rounded joints, let him imagine the scales of a circular form, and so regularly laid on, that the ruler ranges along them in three different ways,—from head to tail, parallel to the deeply-marked lateral line, and in slant angles across the body ;-immediately under the gill-covers, which consist, as in the sturgeon, of but a single plate apiece, let him imagine two strong pectoral fins of 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 latelydiscovered specimen, were furnished on the outer edges by 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-grey 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