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mineral substances; or with some gas. The presence of carbonate of lime, or lime in combination with carbonic acid, is easily shown by the calcareous lining or incrustation of a tea-kettle, or a boiler which has been sometime in use. Some springs contain so large a quantity of calcareous matter that they throw it down as they flow along, incrusting various objects which are placed in them. The springs of Derbyshire England, are particularly remarkable for this, and incrustations of leaves, branches, baskets &c., are easily procured. At the baths of San Fillippo, in Tuscany, where the waters are highly charged with carbonate and sulphate of lime; medallions are formed by first directing the water to a cistern where the sulphate of lime, (gypsum) is deposited. It is then conveyed to a chamber through a tube, from the end of which it falls ten or twelve feet, the current being broken by numerous small sticks crossing each other, by which means the spray is dispersed about the room. The moulds of the medallions are placed underneath, rubbed over with a little soap, and the water striking upon them leaves particles of carbonate of lime, which, gradually increasing, finally gives an exact and beautiful white crust. So rapid is the deposition of earthy matter by these springs, that a stratum of stone a foot thick is annually deposited, and is employed for building purposes. The hill of San Vignorn, in Tuscany, a few miles from San Fillippo, has a thermal spring upon its summit, and from this opening, a deposit of travertine, or concretionary limestone has been formed two hundred feet thick, and of great hardness. We must be careful and not confound these incrustations with true petrefactions. In the one case, as for example an incrusted twig, the inclosed sub

stance will be found to have undergone no alteration, but that of natural decay, but a true petrefaction, is saturated throughout with

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cALCAREous springs, 211

mineral matter, every part of its structure having undergone some change, so that if we break and polish such a specimen, every part of its structure, converted perhaps into flint, may be detected; even the minute ramifications and delicate tissues of many kinds of wood, and most delicate parts of the internal structure of bones. By the infiltration of water through limestone rocks, the sparry concretions are made which depend in caves, like icicles, they are called stalactites, from a Greek word meaning to drop, and also under them, from the drippings, are stalagmites, or drops, and when, as frequently happens, the two unite, a singularly picturesque effect is produced, the caves appearing as if supported by pillars of extraordinary beauty and variety. Sometimes a iinear fissure in the roof, causes the formation of a translucent curtain or partition. This is the case in Weyer's cave, in the timestone range of the Blue Mountains, a narrow and rugged fissure leads to a large cavern where the most grotesque figures present themselves, formed by the infiltration of water through the limestone. Passing from these the passage conducts to a flight of steps that leads into a large cavern of irregular form and great beauty, about thirty by forty feet in dimensions. Here the incrustations hang like a sheet of water that has been frozen as it fell. Farther on is another vaulted chamber, one hundred feet long, thirty-six wide, and twenty-six high ; still farther is anothrange of apartments, at the extremity of which, is a hall two hundred and fifty feet long, having a splendid sheet of rock work running up the centre. The whole length of this extraordinary group of caverns is not less than one thousand six hundred feet. The most celebrated grotto in Europe, is in the island of Antiparos, it consists of a series of caves, the roof, the floor, and the sides of which, are entirely covered with a dazzling incrustation. Immense columns of alabaster extend from the roof to the floor, and others hang in fine cubic forms above the head; the crystalization of alabaster has nowhere else been observed. Although the phenomena produced by incrusting springs, are perhaps not of much importance in modifying or changing the surface of the earth, yet the changes effected by this process, in strata composed of loose materials are of very great importanes: for by an infiltration of carbonate of lime, sand is converted into sandstone, and soft chalk into solid rock, and the loose shells of Florida into compact stone. By this agency, the beds of recent, limestone in which human skeletons are sometimes found, have been formed, and are now in progress of formation, along the shores of the whole West Indian Archipelago. On the north

east corner of the main land of Guadalope is a bed of recent limestone, nearly submerged at high tides. In it are found shells, fragments of pottery, stone arrow-heads, wooden and stone or— naments, and human skeletons. It is quite evident that the rock must have been soft and yielding when these remains were first deposited, they are not fossilized, for the bones still retain their gluten and phosphate of lime. In the wood cut, we give a representation of one of these human skeletons which is now in the British Museum, it is that of a female; the head of this skeleton has been carefully examined by Dr. Moultrie, and is now in the museum of the Medical College at Charleston, South Carolina

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CALCAREOUS SPRINGs.

This skeleton appears, from the craniological developments, to have belonged to a Peruvian, or to some one of a similar race, being entirely dissimilar to the skulls of the Caribs, or ancient possessors of the island. Another skeleton in a sitting posture is in the museum at Paris. The formation of this limestone is as follows. The sea which surrounds the Bermudas, abounds in corals, and shells, and from the incessant action of the waves, the water becomes charged with calcareous matter, and a portion of this is borne by the waves to the shore, and deposited in the form of calcareous sand, which becomes compact limestone, on the infiltration of crystalized carbonate of lime. A great part of the detritus is thrown down in the depth of the ocean, and there envelopes the remains of vegetables and animals, forming new strata for the investigation of future ages. Carbonate of lime is not the only mineral substance held in solution by water, but silicious earth, or the basis of flint, which constitutes so large a proportion of the surface of the earth, is found in great abundance in some springs. It is true, that even in the present advanced state of chemical knowledge, we are unacquainted with any process by which any large proportion of flint can be held in solution by water. Yet we have unquestionable proofs that in the great laboratory of nature, this is effected on a large scale, as for example in the Geysers of Iceland, and the springs of Carlsbad in Bohemia, and the thermal springs of St. Michael, in the Azores. It seems necessary in order that water should contain any large quantity of silica in solution, that it should be raised to a high temperature, and silicious springs are mostly thermal, and are generally found in volcanic regions. The most celebrated thermal springs are those of Iceland, termed the Geysers. The waters of these boiling springs contain a large amount of silex which is deposited on cooling, upon various substances, similar to the incrustations of carbonate of lime already noticed. The hot springs of Iceland are situated in the southwest section of the island, and more than a hundred of them are found in a circuit of two miles. They rise through a thick current of lava, which may have flowed from Mt. Hecla, whose summit may be seen at a distance of about thirty miles. It is said Jo

that the rushing of the waters may be heard as they flow in their subterranean channels. The springs are intermittent, a fountain of boiling water accompanied with a great evolution of vapor, first appears, and is ejected to a considerable height, sometimes as much as one hundred feet, a volume of steam succeeds, and is thrown up with great force and a loud noise, similar to the escape of steam from the boiler of an engine. This operation continues sometimes for more than an hour, though generally not longer than ten minutes, and is succeeded by a period of rest of uncertain duration, and them a repetition of the same phenomena. We give a view of the crater of the great Geyser reduced by Mr. Lyell, from a sketch by J. W. Hooker, M. D. The basin of the great Geyser is an irregular oval about fifty-six feet, by forty-six, the silicious mound of which it is formed, is about seven feet high. In the centre is a pipe seventy-eight feet in perpendicular depth, and about sixteen feet diameter at the top, but contracting to ten feet lower down. The circular basin is represented as

empty, but it is usually filled with a beautifully transparent water in a state of ebullition; the inside of the basin is smooth and formed of a whitish silicious deposit, as are also two channels at

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