I doubt whether Mr. Horner's criterion of the absence of sulphate of magnesia be sufficient. After the removal of the lime he added ammonia without obtaining any precipitate. I think it probable, that a small quantity of sulphate of magnesia, held in solution in a complicated saline liquid, would not precipitate with ammonia, in consequence of the solubility of the triple salt formed. But I have not tried the experiment.

VI. On the Veins of Cornwall. By William Philips, M. G. S.The ore in Cornwall occurs commonly in veins which have an east and west direction, and are called lodes. These are traversed by north and south veins called cross courses; and sometimes by northeast and south-west veins, called contres. The relative antiquity of these veins appears in general to be in the order in which they have been named. The lodes are the most important; they contain tin and copper ore. The tin ore is commonly towards the upper part, and the copper towards the lower part of the lode. No one of these lodes has been traced further than two miles; yet there can scarcely be a doubt that they traverse the whole county, and even pass through Devonshire, till they lose themselves in the channel. No vein has been followed to its greatest depth. Their most common breadth is from one to three feet. They are very rarely 30 feet wide. When a cross course cuts a lode it generally changes its direction, or heaves it, as the miners term it. The contres do the same thing to both the others. The cross courses are usually filled with quartz; though sometimes likewise they con

tain ore.

There is a low range of hilly country that traverses Cornwall just on the south of the principal veins. This range, as far as I observed, was granite. On the north and south side this granite is covered by clay-slate, which goes to an unknown depth. The veins usually traverse the clay-slate, and when they are followed far enough, they are found likewise entering the granite, which spreads itself below the clay-slate. Horn-stone porphyry likewise passes through the clay-slate, but whether in beds or veins has not been determined. It is called elvan by the miners. The top of a lode is usually called gossan, being filled with a yellow ochrey matter to which that name' is given; and lodes have received the following names, according to the prevalent substance with which they are filled:-Gossany, when abounding in gossan: spurry, when abounding in quartz, or fluor spar, both of which are called spar, in Cornwall. The latter commonly green spar or sugar spar: mundicky, when abounding in iron pyrites: peachy, when abounding in chlorite: fleuckany, when filled chiefly with a kind of clay: VOL. V. No VI.

2 F

scovany, when composed of a mixture of quartz and chlorite; not very hard: calpy, when composed chiefly of hard quartz, coloured by a little chlorite: pryany, when the ore does not occur in a compact state; but mixed with the constituents of the lode: grauany, when composed chiefly of granite.

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VII. On the Fresh Water Formations in the Isle of Wight, with some Observations on the Strata over the Chalk in the southeast Part of England. By Thomas Webster, M. G. S.-One of the most remarkable additions which geognosy has of late years received, is an accurate description of the beds which cover the chalk in the neighbourhood of Paris. These beds abound in petrifactions; by a careful examination of which it has been ascertained that some of these beds have been formed at the bottom of the ocean, while others, placed above them, have been formed at the bottom of a fresh-water lake; and these alternations repeated more than once: so that the sea appears to have twice covered the environs of Paris, to have twice retreated while its place was supplied by a fresh-water lake. Immediately over the chalk lie the following beds: 1. plastic clay; 2. coarse lime-stone and sand-stone; 3. siliceous lime-stone, which have been formed at the bottom of the sea. Next comes a bed of gypsum, marl, &c. containing only bones of land animals and fresh-water shells, and therefore formed at the bottom of a fresh-water lake. It constitutes the lower fresh-water formation. Then come beds of marl, containing only sea shells, and therefore of marine formation. It constitutes the upper marine formation. The sixth bed consists of sand and sand-stone, without shells; the seventh a sand-stone containing sea shells; the eighth, the buhr or mill-stone formation, without shells, and argillaceous sand. Then comes the upper fresh-water formation, comprehending marls and bubrs, with freshwater shells. This last formation is covered by alluvial soil. For a particular description of these formations we are indebted to Brogniart and Cuvier.

Though the south-east of England bears this striking resemblance to the north of France, where the Paris basin is situated, that its basis is chalk, which is covered in various places by different beds, yet Mr. Webster was the first person who pointed out a similarity in the formations in certain parts of the south-east of England and those which fill up the Paris basin. The two places where the resemblance is greatest are the Isle of Wight basin and the London basin. In the Isle of Wight Mr. Webster traced an alternation of sea and fresh-water formations similar to those near Paris, and characterized by the very same fossils. The beds, indeed, are not exactly the same in both, though there is a certain degree of resemblance between them. These different formations can be distinctly seen at Headen Hill, upon the north side of Alumbay, not far from the Needles, on the west coast of the Isle of Wight. Henry Englefield first discovered a range of chalk-hills running east and west through the middle of the Isle of Wight. These hills

Sir

terminate on the south side of Alum Bay, and on the north side of the chalk there occur a great number of perpendicular beds of clay and sand, often containing abundance of loose pebbles. Mr. Webster conceives it impossible that these beds could have been formed in the position which they now occupy. He supposes that they were at first placed horizontally over the chalk, and that they were thrown into their present position by some unknown convulsion. Immediately to the north of these beds is Headen Hill, composed of beds nearly horizontal. These beds Mr. Webster considers as formerly lying over the perpendicular beds of Alum Bay, before they acquired their perpendicularity.

The perpendicular beds at Alum Bay are analogous to the lower marine formation in the Paris basin; for all the fossils which they contain, though different from those in the chalk, are of marine origin. The lower fresh-water formation is distinctly seen near the bottom of Headen Hill. It consists of a series of beds of sandy, calcareous, and argillaceous marls, sometimes mixed with brown coal. The thickness of these beds is 63 feet. It contains so many fresh-water shells, and so regularly deposited, that we cannot suppose them to have been carried by rivers into the sea. Besides, in that case we should find a mixture of sea shells, which do not occur in this formation. This is covered by the upper marine formation. It consists of clay and marl, is about 90 feet thick, and contains a prodigious quantity of sea shells. This is covered by the upper fresh-water formation, about 70 feet thick, and consisting of alternate beds of sand, lime-stone, and clay. It contains abundance of fresh-water shells, without any admixture of sea-shells. This formation is covered by alluvial soil.

Mr. Webster conceives the Isle of Wight basin to have been formerly filled with these formations. It consisted of the northern half of the Isle of Wight, extended as far west as Dorchester, and as far east as Shoreham, being bounded on the north by the hills which constitute the South Downs.

The London basin is of much greater extent, but not so well defined. Its southern boundary is marked by Deal, Canterbury, Milton, Chatham, Gravesend, Purfleet, from which it runs southwesterly to Leatherhead and Guildford, and then bending northerly it proceeds as far west as Hungerford. Maidenhead, Eton, St. Alban's, mark part of its northern boundary, and it appears to take in the whole counties of Essex, Suffolk, and Norfolk. The bottom of this basin is chalk. Over the chalk lies a bed of sand, or in some places of plastic clay. Over this lies the London clay, well known for the great number of marine remains which it contains. This clay is mostly covered by a bed of gravel of various thickness, obviously alluvial. Mr. Webster considers the London clay as analogous to the upper marine formation in the Paris basin. The formations formerly placed over the London clay he considers as having been removed by some convulsion.

VIII. Remarks on the Vitrified Forts of Scotland. By Dr.

Macculloch.--These forts have been observed in different parts of the north of Scotland and in Galloway. Nothing is known relative to the time of their erection, or the people by whom they were built. Two opinions have been advanced: that they were vitrified on purpose, and that they were vitrified by accident. Dr. Macculloch shows, by an examination of the stones of which they are composed, that the latter opinion cannot be correct. He examined two of these forts: Dun Mac Sniochain, in Argyleshire, and Craig Phadric, in Inverness-shire. In both the walls consist chiefly of primitive rocks. These have been mixed with a considerable quantity of a kind of amygdaloid, which easily fuses, and by the fusion, more or less complete, of this material, the vitrification has been brought about. The amygdaloid differs considerably in its nature at the two forts. At Amworth, in Galloway, there is no amygdaloid; the rocks are grey-wacke and grey-wacke-slate. Some portions of this grey-wacke are fusible, from a mixture of calcareous spar. Accordingly this fort is only vitrified in a few detached spots.

IX. On the Sublimation of Silica. By Dr. Macculloch.-He had exposed a mixture of the oxides of tin and lead in a crucible covered by another, for some hours, in a furnace at a heat conjectured to be between 130° and 140° Wedgewood. On cooling, the top of the uppermost crucible contained some small filamentous crystals, white and brilliant, crossing each other in all directions. They were found to be crystals of pure silica. Dr. M. was not able to repeat this experiment with success.

X. Observations on the Specimens of Hippurites from Sicily, presented to the Geological Society by the Hon. Henry Grey Bennet. By James Parkinson, M. G. S.-These specimens are so perfect as to enable Mr. Parkinson to determine some things respecting the original structure of the shells. The supposed operculum mentioned by Picot la Peyrouse could not be distinguished. Mr. Parkinson thinks that the hippurites, orthoceratites, ammonites, &c. had the means of elevating themselves to the surface of the sea, like the nautilus; and some things which he observed in these specimens give countenance to this idea.

(To be continued.)

ARTICLE XI.

Proceedings of Philosophical Societies.

ROYAL SOCIETY,

On Thursday, the 27th of April, a paper by Mr. Seppings was read, containing further particulars respecting his improved mede of ship-building. As, immediately after his last paper a paper was read to the Royal Society, containing theoretical objections against a mode of building ships to which in his opinion theory was not

competent, it occurred to him that it would be satisfactory to the Society to lay before them the results which have been obtained by an investigation into the ships built according to his mode. He stated the report of Admiral Durham respecting the Tremendous. She was the best sailing ship in his fleet. Three years afterwards she was examined by professional ship-builders, and found not to have suffered any deterioration. Other similar reports were mentioned. Dr. Young's allegation, that the oblique braces were imitated from the French, is, according to Mr. Seppings, inaccurate. The French had indeed introduced some pieces of oblique timber, and they were to be seen in a ship which we took from them; but they had not been attended with any benefit, and were abandoned as useless by the French themselves. Mr. Seppings's mode is quite new, and the benefit of it sufficiently obvious.

On Thursday, the 4th of May, a paper by Sir Humphry Davy was read, on the action of acids on hyper-oxymuriate of -potash. In consequence of the discovery of a new acid by Gay-Lussac by treating hyper-oxymuriate of barytes with sulphur, Sir H. Davy was induced to examine more carefully than had hitherto been done the action of acids on the hyper-oxymuriate of potash. When sulphuric acid is poured upon this salt in a wine-glass, very little effervescence takes place, but the acid gradually acquires an orange colour, and a dense yellow vapour of a peculiar and not disagreeable smell floats on the surface. These phenomena led the author to believe that the substance extricated from the salt is held in solution by the acid. After various unsuccessful attempts to obtain this substance in a separate state, he at last succeeded by the following method. About 60 grains of the salt are triturated with a little sulphuric acid, just sufficient to convert them into a very solid paste. This is put into a retort, which is heated by means of hot water. The water must never be allowed to become boiling hot, for fear of explosion. The heat drives off the new gas, which may be received over mercury. This new gas has a much more intense colour than euchlorine. It does not act on mercury. Water absorbs more of it than of euchlorine. Its taste is astringent. It destroys vegetable blues without reddening. When phosphorus is introduced into it, an explosion takes place. When heat is applied, the gas explodes with more violence, and producing more light, than euchlorine. When thus exploded, two measures of it are converted into nearly three measures, which consist of a mixture of one measure chlorine and two measures oxygen. Hence it is composed of one atom chlorine and four atoms oxygen. It is not unlikely that euchlorine is a simple mixture of three measures of chlorine and two measures of this new gas; but the point cannot be determined till it be known whether Dutch foil will burn in such a mixture as it does in euchlorine. This experiment the author could not try, because at Rome, where he then was, he could procure no Dutch foil fit for his purpose. The same gas is disengaged from hyper-oxymuriate of potash by nitric acid, and with still greater facility; but it is always mixed with one-fifth of