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, the author said, for his late friend, Mr James Brown, a young chemist, who, by his labours and discoveries in the science to which he had devoted himself, gave promise of an active and useful life, which was, however, cut short by an attack of cholera, that in a few hours proved fatal. His retiring manners and devotion to his work made him unknown, save to a few friends, who were thus unexpectedly called to mourn the loss of one who seemed destined by his labours to command the respect of the scientific world; and the collection was some months ago placed in the hands of the writer by his father. It consists of nearly 1000 different specimens, with accompanying manuscripts, drawings, and sections, most elaborately executed. Valuable memoirs had been published by Mr Bain on the geology of South Africa; but he did not seem to have visited Du Toit, the locality where the fossils on the Society's table had been gathered, as it was not mentioned by him. Du Toit is about thirty-five miles north-west from Swellendam. It is situated on the further side of the Lange Bergen Mountains, on the oldest beds of what, from palæontographical evidence, seems to be the Old Red Sandstone. The fossiliferous beds are composed of coarse sandstones and shales. The fossils are chiefly brachiopod mollusca, and include Spirifer antarcticus, and Orbignii, Terebratula Bainii, Orbicula Bainii, &c., Solinella antiqua, and other bivalves. Besides these there were only some Encrinite stems, and the cast of a Trilobite, neither of which could be more specifically described, owing to their bad preservation. Mr Carruthers noticed the remarkable condition in which the clay slates of the metamorphic series exist in the vicinity of Swellendam, where they have little more consistency than dried alluvial brick clays, so soft as to have permitted Mr Bain to drive a tunnel of 400 feet through them by the aid of the pickaxe and spade alone. The induration increases, however, until in other localities the rocks become, as Mr Douglas says, "exceedingly hard, siliceous, and splintery, so as to cut the hand when incautiously griped." VII. Ornithological Notes. (Specimens were exhibited) (1.) The Gadwall, Anas strepera, Linn. By P. A. DASSAUVILLE, Esq. This species being of rare occurrence in Scotland, Mr Dassauville thought it might be of interest to show the two specimens now before the Society. They were shot on the Tay, near Newburgh, in the beginning of April, and are a male and female, as was proved by dissection, the ova of the female being numerous, but not far advanced. Mr Dassauville was aware of the danger that specimens obtained, as these were, in the poulterers' shops, might not be actually procured in this country, since importing wild fowl from the continent was so general; but the specimens under notice were evidently so recently shot-the feet and webs being quite soft and flexible that he had no hesitation in believing they were killed in this country, without other evidence; however, he had been obliged with a sight of the invoice which accompanied them, dated from Perth, and felt satisfied there was no room to doubt that they were procured from the locality mentioned. One or two sessions ago Dr J. A. Smith exhibited to the Society specimens of the gadwall, and these were the only others he had seen that were killed in Scotland. (2.) The Shoveller, Anas clypeata, Linn.; the Great Grey Shrike, Lanius excubitor, Linn.; the Shore Lark, Alauda alpestris, Linn. By JOHN ALEXander Smith, M.D. Dr Smith said, he was disappointed in not being able to exhibit a very fine pair of Shovellers (Anas clypeata), male and female, which he had examined; they were shot near Kincardine, on the Forth, about the 1st of April. The birds were now the property of Robert Chambers, jun., Esq., and as they were rare in this neighbourhood, their capture was worth putting on record. He exhibited an adult male Cinerious Shrike, Lanius excubitor, which was one of our occasional visitors, and far from common; it was noticed to occur generally in the beginning of winter. This bird was got on the 30th of March at Tulliallan, near Kincardine, on the Forth. Mr James Miller, the gamekeeper who shot it, had never seen a specimen of the bird before, although he had lived for many years in the district. The last bird Dr Smith had to notice was the Shore Lark, Alauda alpestris, Linn. It is a bird of very rare occurrence, being apparently only an accidental straggler in this country; in the north of Asia, Europe, and especially America, it abounds, and migrates southwards in the autumn to more temperate regions. The first specimen noticed in England was in 1830, and only one or two have been observed since. He had not been able to find any recorded as taken in Scotland. This bird was killed by Mr Evans, Tynefield, about the 10th of January last, near the mouth of the Tyne, and its plumage was unfortunately, much destroyed by the shot. It is a fine old male, having the back brown; tinted on the head, neck, and shoulders, of a rich vinaceous colour; the streak over the eye, the forehead, and the ear-coverts, yellow; and with the lore and a gorget of black; under parts dull white, and flanks pale reddish brown; axillaries white. It is the property of Dr C. Nelson, Pitcox, near Dunbar, to whom it was presented. By JOHN VIII. Notes on the Crania of the Urus (Bos primigenius) in the Some years ago, when gathering up various details in reference to the ancient small short-horned cattle of this country, my attention was also directed to the large cattle (Bos primigenius), and to the specimens of crania in the Museum of the Society of Antiquaries. I took various measurements of these crania, and searched the early records of the Society for such information in regard to the places where they were found, and any other details that might be of interest; and as Mr Turner has favoured us this session with some details of the specimens of this great ox in the Anatomical Museum of the University, I have thought it might interest the members if I produced my old notes on the subject. There are three specimens of these crania of the Bos primigenius in the Museum of the Society, marked Nos. 2, 4, and 5 of the "Fossil Skulls," &c., in the printed Catalogue of the Museum, and the following table gives some of their measure The cranium No. 4 was the one first presented to the Museum of the Society, by the Rev. Thomas Robertson, minister of Selkirk, in 1781. The donation was made through a Mr Cairncross, and the following letter accompanying it is preserved in the library of the Society: To Mr George Cairncross, Writer, Parliament Close, SELKIRK, July 14th, 1781. "DEAR SIR-Among other curiosities dug out of a marle moss at Whitmuirhall in this parish, the skull and flints of an ox which I have sent you attracted my attention. You, I know, are fond of anything that tends to throw light upon the ancient state of this country, and therefore I used the freedom to transmit this, not merely on account of its uncommon size, but as a proof of the large breed of cattle with which this country abounded in the last century. I found five skulls, evidently larger, but not so entire. I found also several small axes, resembling those used by coppersmiths, but did not |