DESCRIPTIVE SKETCHES

FROM A

GEOLOGIST'S PORTFOLIO.

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 reünited, 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 half through 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 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 bonebed, coupled with at least one of the causes to which it owes its origin, in the upper part of the Moray Frith. 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 burial-ground, - 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 haddock 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 gillcovers, which consist, as in the sturgeon, of but a single plate a-piece, let him imagine two strong pectoral fins of