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strata composed of loose materials are of very great importance 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, havo 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 ornaments, 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 CarolinaCALCAREOUS 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. Michæl, 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 laya, which may have flowed from Mt. Hecla, whose summit may be seen at a distance of about thirty miles. It is said
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 then 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 df the great Geyser is an irregular oval about fifty-six feet, by forty-six, the silicious mound of which it is formed, is about seyen 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
SILICIous springs. 215
each side, by which the water escapes when the basin is full. It is said that an eruption may be brought on in a few minutes by throwing stones down the pipe, these are again ejected, oftentimes with immense violence. The theory of the action of these hot springs of Iceland has not yet been satisfactorily given; the heat however, is supposed to be derived from subterranean volcanic fires. The silicious water from these springs incrusts plants, twigs, and leaves, similar to the calcareous springs. In the island of St. Michael there are hot springs very strongly impregnated with silica; wherever the water has flowed, sinter or precipitated rock, is formed intermixed with the clay, including grass, ferns, and reeds, in different stages of petrefaction; branches of the same ferns which now flourish in the island are found completely petrified, preserving the same appearance as when vegetating. There are many springs in this country which depositsilicious and calcareous matter. Iron is found in the waters of almost all springs, and some of them are so copiously impregnated with this metal that they stain the rocks or herbage over which they flow. The iron which is thus borne out of the earth and deposited into the sea, acts as a cement to bind together the subaqueous deposits now forming.
glomerate. Occasionally nails, or other pieces of iron, are found in the centre of a hard nodule of sandstone, formed by this process. The engraving, from Dr. Mantell’s “Wonders of Geology,” is a very interesting specimen, it is a conglomerate of glass beads, knives, and sand, cemented together by an infiltration of iron, derived from the oxidation of the blades. It contains two silver pennies of Edward I, and was dug up at a depth of ten feet in the river Dove in Derbyshire. The coins are presumed to have been a part of the treasures contained in the military chest of the Earl of Lancaster, which was lost in crossing the river in the dark; more than five centuries must therefore have elapsed since its submersion. The ore called bog-iron, is formed by the infiltration of water impregnated with iron, and various kinds of wood are colored black by the same cause. Iron, it is well known is one of the chief ingredients in many celebrated mineral waters, frequently in the shape of a carbonate. The consolidation of sand and other loose materials by the agency of mineral waters, is everywhere going on, and in much greater extent than can be easily comprehended; small and apparently simple as are the means employed, yet the effects are magnificent. The detritus borne down by the mountain streams falls at last, quietly into the ocean, or is deposited upon the rich soil of some delta, after a certain time the mass is cemented together by other mineral ingredients dissolved in the water, and beds of compact stone, in which are entombed the remains of animate and inanimate existence, are formed slowly but surely, for the use of most distant generations. The twigs and leaves, and insects, which fall into the petrifying springs are incrusted with a coating of stone, or are slowly transmuted into mineral substance for the inspection and admiration of a future race. Thus the change continually goes on. The frost, the storm, and the stream, and in many volcanic districts the carbonic acid, continually given off, as for example, in the neighborhood of the extinct volcanoes of Auvergne in France, cause even the granite rocks to crumble and fall away; but in a thousand other places the process of reunion is going on, and different kinds of stone are being formed
from the ruins of the old. Besides the springs to which we have N