had lost the whole of the outer or inhabited chamber, but the triangular shape of the aperture was distinctly shown by the compressed ventral margin of the remaining part of the shell. The position of the siphuncle-said to be close to the dorsal margin-seemed to be indicated by a small deposit of iron pyrites, probably caused by the organic matter having been longer retained in that canal. The interior of the shell was filled with a ferruginous clay, containing a large proportion of carbonate of lime, a stalagmitic layer of which was seen encrusting a portion of the mass. Defoliation of the outer porcellanous coat of the shell had taken place, but what remained of the inner nacreous layer showed the striæ of growth bending sharply backwards in well-marked undulations. If the proportions of the fossil specimen were similar to those of the recent Nautilus pompilius, the shell, when entire, would have measured about fifteen inches in diameter. Dr M'Bain stated that the Nautilida were in some respects the most interesting family in the molluscan sub-kingdom. They formed the type of the second order, Tetrabranchiata of Owen, in the class Cephalopada, of which upwards of 1400 fossil species have been disinterred from the Paleozoic and Mesozoic rocks. Of all the genera constituting the Tetrabranchiate order of mollusca that existed in the ancient seas, the nautilus was the only one that had been found to pass into the tertiary formations, and there were at least two species still existing in the seas of the tropics. Six fossil nautili were stated by Mr Edwards to have been found in the older Eocene deposits of England, and four of these had been obtained from Sheppy-the N. centralis, N. urbanus, N. imperialis, and N. Sowerbyi. That island was well known to palæontologists as a rich depository of organic remains. It was situated on the south side, at the mouth of the Thames, and separated from the county of Kent by the East Swale, and estuary of the river Medway. The greatest length of the island, from the garrison at Sheerness to Warden Point, the easternmost extremity, was about ten miles, and it was from five to six miles in breadth. The geological structure consisted of a vast deposit of dark gray or brownish clay, rising to the height of nearly 500 feet above the sea, with

interstratified layers of concretionary nodules, commonly called septaria or cement stones. This clay belonged to the lower tertiary formation, and formed a part of the London basin-one of those isolated fluvio-marine deposits which took place in hollows of the chalk subsequent to the cretaceous epoch. On the north side of the island, and eastward from Sheerness, the cliffs rise to the height of from one to two hundred feet, and, chiefly from atmospherical causes, were constantly crumbling down in large prismatic masses, which gradually broke up, and formed a flat shore of fine silt. Mud banks extended off shore for about half a mile, and at low water workmen were employed in procuring the cement stones. The beach was not more than from ten to twenty yards wide, on which were strewed abundance of fossil fruits, wood, crustacea, and mollusca, which had fallen out of the clay. Dr M'Bain said, he had frequently obtained upwards of a hundred Eocene fossils in a single excursion, and that the remains of fish and reptilia were also of frequent occurrence in the London clay of the Island of Sheppy. He added, that many of these Eocene fossils became mixed with recent organisms, and were buried together in the re-composed silt, which the hasty generalization of some palæontologist, in a future new geological epoch, might consider as a sufficient proof that they also lived together at the same time in the Cainozoic period.

(2.) Notice of the Nucula decussata, found in the so-called Raised Seabeach Bed at Leith. By JAMES M'BAIN, M.D., R.N.

The members of the Society, Dr M'Bain said, were no doubt familiar with a bed of sand and gravel extending along the shores of the Forth in a more or less continuous manner, and generally known as the raised sea-beach bed. This deposit had been considered by several eminent geologists to represent an ancient sea-beach, which, in consequence of a general elevation of the land, had been raised twenty feet or more above the level of the sea, at a comparatively recent geological period. This view was strenuously opposed by the late Professor John Fleming, who maintained that this so-called raised sea-beach bed and other accumulations of a similar

VOL. II.

structure, at still higher levels, derived their origin from ground storms" or sudden risings of the sea, by which shells, sand, and gravel, had been placed in situations now considerably removed from the influence of the tide. Professor Fleming had arrived at this conclusion as early as 1806, from examining a bed of shells, chiefly composed of the common oyster shell, to the westward of the town of Borrowstounness, in the county of Linlithgow, and stretching along the banks of the Forth into Stirlingshire. The raised sea-beach controversy forms nearly the whole of the last chapter of his last work—“The Lithology of Edinburgh." Any new fact, therefore, connected with this distinct marine deposit would be of interest. This raised sea-beach bed is well exposed in many parts of the coast between the sandstone quarry at Granton and the Magdalen Burn near Fisherrow. It varies in thickness from two to ten feet, and contains abundance of comminuted shells, with many in a more or less perfect state of preservation. The horizontal position of the bed in respect to the present high-water level is by no means equal. At Granton quarry, the base of the bed is about ten or twelve feet above high-water mark, and rests upon the sandstone and boulder clay; whereas a quarter of a mile to the eastward, at a ledge of rocks projecting sea-ward, it is only two or three feet above high-water level. The bed is then interrupted by a sea-wall, until at the east end of the village of Newhaven, at the collection of boulders that form a boat harbour, it is again observed nearly on a level with high-water.

From this point eastward the bed gradually rises in height, and at an interesting geological section of the boulder clay called the Man-trap, the base of the bed is seen to rest on the clay, 15 feet above the high-water line. It is then lost sight of by the sea-wall in front of the artillery barracks; but Dr M'Bain had lately an opportunity of seeing it exposed in a digging for a drain, at the north end of Albany Street, where it appeared about seven or eight feet above high-water. Nearly in a line with this digging, and south of the road opposite the west end of Leith Docks, a foundation for a large building was begun a month or two ago; and in watching the progress of the work, after the removal of two or three feet

of artificial soil, the continuation of the sand and gravel bed was observed to cover the boulder clay at six or eight feet above high-water level. In a section made for the foundation of the east wall of the building, the boulder clay was cut down to the depth of 12 or 14 feet; and in the sand and gravel-bed overlying the clay at this part, amongst other shells usually found in this bed, a detached right valve of a Nucula was obtained, having the sculpture and characters of Nucula decussata. The epidermis was well preserved, and of an olivegreen colour. It was marked with concentric wrinkles, and strongly raised radiating striæ, with short but distinct transverse plicæ on the dorsal area. The inner surface was pearly white, and had a crenulated margin, with twelve pectinated teeth in front of the cartilage-depression, and about double that number behind. The valve was rather more elongated, and larger than the ordinary examples of the common Nucula

nucleus.

The N. decussata is not recorded as having been found in the Firth of Forth, but it lives on the west coast of Scotland, and in the Hebrides, and is said by Löven to be a Swedish shell. The specimen was accidentally broken, and the fact of the valve having been found is only recorded to direct attention to a closer scrutiny of the marine contents of this deposit, especially in sections inland from the present high-water level; as the lateral extent of this so-called raised sea-beach bed, and its relation to other accumulations of a similar lithological structure, but destitute of any trace of marine remains, had not been satisfactorily determined.

IV. Contribution to a Monograph of Iceland Spar. By ALEXANDER BRYSON, Esq. Part I.

This communication will be given complete (along with Part II.), in a future fasciculus of the Proceedings.

V. On a Method of constructing Polarizing Prisms of Nitrate of Potash. By T. STRETHILL WRIGHT, M.D.

Dr Wright stated that many doubly-refracting substances, when immersed in dense and transparent fluids, had, as was well known, the property of polarizing light. This polariza

tion of light was not effected by the whole surface of the substance, but only by inclined parts of it which intersected the ray in an oblique direction. In passing through such parts a beam of light was divided into two rays polarized in opposite planes. The one ray continued its original course, while the other suffered deflection proportionate to the inclination of the polarizing surface, and was thus entirely thrown out of the field of view. It occurred to the author that large crystals, having their surface artificially inclined, might, when immersed in a highly refractive fluid, be used as polarizing prisms, and he had succeeded in thus forming polarizers, one of which he placed before the Society, and which was found to be well adapted for application to the microscope. It consisted simply of a wedge of nitrate of potash, cut from one of the angles of a large crystal, and put up in a cell filled with castor oil.

Dr Wright stated that very beautiful objects for the polariscope might be formed of clear plates cut from the surfaces of large crystals of nitre, and grooved in various designs. These, mounted on a colouring plate of mica, and enclosed in a plateglass cell filled with oil of turpentine, gave rich effects of changing tint when traversed by light reflected from a glass plate or from the northern sky. Large planes of parallel polarizing crystals might be produced by crystallizing muriate of morphia on slightly inclined plates of glass, and might be removed so as to leave designs. These figures, when mounted in Canada balsam, with colouring plates of mica, gave curiously dazzling binocular effects, or when viewed with both eyes, as the two images differed in colour for each eye. In examining objects of this class, it was necessary to stop off all rays but those passing at right angles to the polarising plate.

VI. Notes on the Geology of Swellendam, South Africa. By WILLIAM CARRUTHERS, Esq. (Specimens of the rocks and fossils were exhibited.)

The specimens which formed the subject of this notice were gathered and sent to this country by Mr Robert Douglas, a self-educated and enthusiastic geologist. They were intended,