which name the nations of the Kirghiz designate the Lecanora esculenta." Several occurrences of what is called a fall of manna are attributable to the accumulation of the lichen, Lecanora esculenta Aucher-cloi,* observed in Persia in layers of nearly inches (0 m. ·12 to 0 m. 18) in thickness, He sent specimens, with the following note, to France :- In 1829, during the war between Persia and Russia, there was a great famine in Oroomiah, south-west of the Caspian. One day, during a violent wind, the surface of the country was covered by a lichen, which fell from heaven. The sheep immediately attacked and devoured it eagerly, which suggested to the inhabitants the idea of reducing it to flour, and making bread of it, which was found to be good and nourishing. The country people affirm, that they had never seen this lichen before nor after this time." "During the siege of Herat (which is about 876 feet above the sea), more recently, the papers mentioned a hail of manna which fell upon the city, and served as food for the inhabitants.?! A rain of manna occurred, April 1846, in the district of Jenischehir, and formed a layer three or four inches in thickness. It was of a greyish white colour, rather hard, and irregular in form, inodorous and insipid." "Pallas observed it in the mountainous, arid, and calcareous portion of the great desert of Tartary. M. Eversham collected it in the steppe of the Kirghiz, to the north of the Caspian Sea, where it is called semljenoi-chleb. M. Ledebour has observed it in the same countries, but chiefly those which border on Altai and Bilezikdgi ; saw it also in Anatolia, in 1845. Dr Leveillé gathered it in Crimea, and Dr Guyon recently in Algeria." "It is found in irregular shaped bodies, varying in size from that of a pin's head to a pea or small nut; and when seen in its proper sites, has never been found attached to any support whatever. analysis of the Lecanora shews that there is no fecula in its compo sition." An Wellsted, p. 49, "learned from a Jewish Rabbi, that, on his journey through the desert contiguous to Damascus, far removed from trees or vegetation of any kind, a substance was deposited, which, from his description, in appearance, size, and flavour, accurately resembled the manna of the Scriptures. Similar testimony was derived from several Bedouins." It may be remarked, in passing, that several writers have not hesitated to identify some of these species with the manna miraculously supplied to the Israelites in the wilderness. They were obviously acquainted with manna of some kind, from the fact that they named the new substance from its resemblance to it.—American Journal of Science and Arts, Second Series, vol. ii., No. 9, p. 350. *Relat. d'un Voy. en Orient., vol. ii., p. 399. On the Temperature of the Geyser Springs in Iceland, M. Flourens communicated to the Academy of Sciences on the 16th of November, the results of some observations of MM, Descloizeaux and Bunsen last July, on the intermittent boiling springs of the Geyser and Strockr, the latter being within 140 yards of the Great Geyser. The observations were on the temperature of the water, in the great column or well of each, made by suspending thermometers at different depths, at different times, before and after eruptions. The Great Geyser has a depth of 22 metres (72 feet), and the experiments shewed that the temperature of the column diminished gradually from the bottom upwards, and that the maximum temperature at the bottom before a great eruption was 127°.6 Centigrade (2604° Fahr.), and the minimum 122° (2511° Fahr.), after an eruption. The temperature of the water at the surface was 85°2 (185° Fahr.), when that at the bottom was 127° C. After an eruption, the lowest thermometer stood at 121°6 (251° Fahr.); nine hours afterwards at 123°·6 (2541° Fahr.). Between 11 o'clock A.M. of the 6th July, and 2·55 P.M. of the 7th, there was no eruption, so that there had been an interval of nearly 28 hours and the water at the latter time, at the bottom, was 127°6 (2614° Fahr.); a quarter of an hour afterwards there was a slight eruption. ; The Strockr is a circular well 441 feet deep, with an orifice of about 8 feet, which rapidly diminishes downward, and at about 271⁄2 feet from the surface the orifice is only 10 inches. The column of water between the eruptions has a mean depth of 27 feet, so that its surface, which is in a constant state of ebullition, is generally from 10 to 13 feet below the surface of the ground. The temperature of the water at the bottom varied from 112 9 to 114°2 (235° to 2371° Fahr.), and the same temperature continued throughout a depth of about 20 feet, when it began to sink, and at the surface of the water the thermometer stood at 100° (212° Fahr.). These observations on the temperature of the water are highly curious and important. We have a temperatnre of 261° Fahr. at the bottom of a free open column of water, in which thermometers could be suspended on a line dropped from the surface, while it might have been expected that, as soon as a film of water at the bottom was raised to a higher temperature, it would ascend, and be replaced by a colder and heavier film, and that thus a constant current would * It is called Strokkus in the Comptes Rendus, but Henderson calls it Strockr, and says the name is derived from the verb "Strocka," to agitate, or bring into motion. † Henderson's Iceland, p. 69. be established throughout the column, until the whole arrived at a temperature of 212°, when ebullition would commence and continue. The pressure of the column of water may perhaps account for the high temperature at the bottom, especially if the free circulation be impeded by the sides of the well not being vertical, and still more by projections in the sides causing contractions of its diameter. But the experiments of M. Donny, of the University of Ghent, published in the 17th volume of the Memoirs of the Royal Academy of Sciences and Belles Lettres of Brussels, on the Cohesion of Liquids, may perhaps be considered as throwing some light on this phænomenon of the Geyser. By a series of carefully conducted experiments, M. Donny has shewn :— 1. That the constancy of the boiling point of water, under ordinary atmospheric pressure, depends upon its containing a considerable quantity of air. 2. That there is a marked difference between the boiling point of water containing air, and of water freed from air. 3. That a small quantity of air dissolved in water, is sufficient to attenuate greatly the cohesion existing between the molecules of the water. 4. That when water is freed from air, as far as that is possible, the cohesion of the molecules is so increased, that a higher temperature is necessary to overcome it, and that the boiling point is very considerably raised. M. Donny succeeded in raising the temperature of water so freed of air to 135° Centigrade (equal to 275° of Fahr.), under the ordinary atmospheric pressure, without its exhibiting any symptom of ebullition, shewing, that the cohesion of the molecules was nearly equal to the pressure of the three atmospheres on water containing air. This is a fact most important to bear in mind in reasoning upon many geological phænomena, particularly those connected with the solution of silica. The further researches of M. Donny, recorded in the same memoir, appear also to offer an explanation of the violent and intermittent eruptions of the Geyser; for he states, that if water deprived of air be exposed to so considerable an increase of temperature as to overcome the force of the cohesion of the molecules, the production of vapour is so instantaneous and so considerable as to cause an explosion. As water long boiled becomes more and more deprived of its air, M. Donny attributes the sudden bursting of the boilers of steam-engines to the same cause.-Address delivered at the Anniversary Meeting of the Geological Society of London. By Leonard Horner. On the Origin of the Sand-hillocks of St Ives Bay, Whitesand Bay, and Mount's Bay. By RICHARD EDMONDS, jun., Esq.* The sand-hills of St Ives Bay, which are almost entirely covered with turf, the arundo arenaria, mosses, and other plants, occupy some square miles of the northern coast of Cornwall, and consist chiefly of comminuted marine shells, carried from the shore by violent winds. They are called "the Towans" from the Cornish word towyn, "a turfy down," the word "down" being, perhaps, a mere corruption of "towyn" by the very common change of the letter t into d. And it is remarkable that the name Les Landes,†"barren heaths," given to the sandy district on the south-western coast of France, is almost precisely the same with Lelant, the parish in the Towans, where an ancient market-town is said to have been buried by the sand. Hence, Towans, Downs, Lelant, and Les Landes (here, again, the t is converted into d) may be all regarded as synonymous. Some suppose, according to an old tradition, that these sand-hills, with the exception of a few feet immediately below the surface, were blown in during one tremendous tempest. Others, judging from the dark horizontal lines-the remains of old vegetable surfaces-which occur at various depths within a few feet of the present surface, and which alternate with layers of light sand, consider that the hillocks were formed by a succession, at distant intervals, of thick deposits, which always buried the then growing turf, and sometimes to considerable depths. § A third hypothesis which I would suggest is, that the sand * Read before the Royal Geological Society of Cornwall, on the 15th of October 1846. † Lande "grande etendue de terre qui n'est pas propre au labour." Dictionaire Breton. A similar opinion prevailed in reference to the sand-banks of Mount's Bay. See Trans. of the Royal Geological Society of Cornwall, 1826, p. 179. § See Sir H. De la Beche's Geological Report of Cornwall, Devon, and Somerset, p. 445. has, for the most part, accumulated imperceptibly upon a continuously growing vegetable surface, the deposits during a single storm being too slight to cover the herbage or to check its growth, except occasionally, when they were sufficiently copious to bury it entirely; yet not so deeply but that the turf has soon reappeared, and the gradual accumulation has proceeded as before. These occasional complete coverings of the herbage may be inferred from the dark lines or vegetable remains above noticed, and even in their absence from the perfectly preserved land shells which are frequently found more numerous in horizontal lines than in the sand immediately above or below them; for these lines, although not dark, are like the former, most probably, sites of old vegetable surfaces whereon the inhabitants of the shells subsisted. Generally, however, the shells are not thus unequally distributed, but occur precisely as if the sand had been gradually accumulating and burying them, without ever completely covering the growing turf whereon the animals were feeding or hybernating. A few months since, while examining some of the deep cuttings in the hillocks about a mile from the sea, I discovered, at the depth of about 50 feet, imbedded in a uniform mass of sand, a great number of small land-shells, within a space only half an inch thick and three inches square. The shells were mingled with sand; and as they consisted of not less than ten different species, the space, probably, small as it was, included several nests. From the perfect preservation of these shells, and from the impossibility of their inhabitants finding subsistence on the bare sands, I conclude that they, as well as the numerous other land-shells which occur in an entire state in the hillocks at all depths, must have been imbedded in situ—in contact with vegetable surfaces, whose former existence, it appears therefore, is now generally indicated only by the exuviæ of the animals which once pastured on them. The shells found in the small space above described, are of the following species, in various stages of growth :-helix virgata, and pulchella; zonites radiatulus; zua lubrica; bulimus acutus; pupa umbilicata, marginata, and anglica; vertigo |