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Jet, of which necklaces, ear-rings, and other ornaments are made, is but a variety of coal, as common in its origin and nature as that which we pile on our fires. It is occasionally found in the lignite beds of England, but principally in Germany and Prussia, where it occurs associated with amber, which is regarded as a fossil gum, while jet seems to be the trunk and branches of trees more completely bituminised and freer from earthy impurities than cannel or other coals.-Amber, a wellknown yellow resin-like substance, is believed, as stated, to be a fossil gum or resin; and its connexion with deposits of lignite seems to confirm that opinion. It is solid, brittle, commonly transparent, and when rubbed, becomes electrical. It is found in various countries, more particularly on the Adriatic and Sicilian shores; on the Baltic, between Memel and Dantzic, where there are regular mines of it; and in Japan, Madagascar, and the Philippine Islands. It is used chiefly in the manufacture of beads and necklaces, and in the preparation of varnishes. The largest known specimen of amber was found near the surface of the ground in Lithuania, about twelve miles from the Baltic: it weighs eighteen pounds, and is in the royal cabinet at Berlin. Other curious specimens have been detected enclosing insects, and even drops of water-these apparently having been enclosed when the gum was exuding in a fluid state from the living tree.

Naphtha-Petroleum-Asphalte.

Naphtha, petroleum, mineral pitch, and asphalte, may in a great measure be regarded as one and the same substance in different degrees of concentration and purity. Thus naphtha, on exposure to the air, soon loses its limpid appearance, and passes into petroleum; and petroleum, under similar treatment, shrinks into a viscous slaggy state, undistinguishable from mineral pitch. Natural naphtha is a limpid, or but slightly-coloured bitumen, highly inflammable, and of a strong bituminous, but not disagreeable odour. It is found at Baku on the Caspian, at Hit on the Euphrates, and at other places in Mesopotamia; it occurs abundantly in the lower districts of the Birman empire; is found at various places in the north of Italy, as Piacenza, Modena, &c.; and in some districts of North America. It generally exudes from fissures in the rocky strata, or is collected in shallow wells, dug in the clays and shales where it occurs. A similar liquid can be obtained by distilling petroleum, coal-tar, and other bitumens; but the artificial product has a more penetrat ing and unpleasant odour. Naphtha has the property of dissolving most of the essential oils and resins, and is at present largely used as a solvent of caoutchouc. It is also used for lamps; and the cities of Parma and Genoa are said to be lighted with the produce of the wells in the duchies of Modena and Parma,

Petroleum, or rock-oil, is another liquid bitumen, of a brownish colour and variable consistency, and yielding a strong disagreeable odour. It is found exuding from various secondary strata, but chiefly in coal districts, where it is evidently a product of that formation. It occurs in small quantities in various localities of Britain, but abundantly in other countries of Europe, in Persia, the Birman empire, in Texas, and in the islands of Trinidad and Barbadoes. On exposure to the air, petroleum thickens, and assumes a darker hue, in which state it is generally known by the name of mineral pitch, or Barbadoes tar. On further exposure, and especially when mingled with earthy impurities, it passes into a solid state, then becoming the common asphalte or bitumen of commerce. In its ordinary liquid state it is burned for light; worked into balls with earth and gravel, it is used in eastern countries as fuel; and mingled with grease, it is occasionally employed as a substitute for tar in coating vessels.

Asphalte, so called from its adhesive nature, differs from mineral pitch in being solid and brittle at the ordinary state of the atmosphere. It melts easily, and is highly inflammable, leaving, when pure, little or no ash after combustion. It is found in most of the localities where petroleum springs occur, being nothing more than their accumulated produce. The chief supplies are obtained from the shores of the Dead Sea, from Barbadoes, from Trinidad, where it occupies a basin or lake about three miles in circumference, and from Clermont, Seyssel, and Bourg in France, where it occurs in limestone and calcareous shales. Asphalte was employed by the ancients in some of their cements, and also in the process of embalming. It is now extensively used in the formation of pavement, roofing, and other economical purposes. Melted and mingled with properly sifted gravel, or iron slag, it forms a very durable and unexpensive pavement, being liable to be softened, however, during intense heats.

CALCAREOUS SUBSTANCES.

Under this head we include such economic minerals as contain a notable proportion of calx or lime in their composition. Common limestone, magnesian and lithographic limestones, marble, chalk, marl, gypsum, and alabaster, are familiar examples. Some of these have evidently been deposited from calcareous waters; others are as evidently the production of animalcules, like the coral insect; and some are almost wholly composed of the shells of molluscs, and of other calcareous exuviæ. Whatever may have been their several origins, they have all undergone certain chemical and structural changes since their formation—thus rendering them less or more compact and crystalline, producing a dull massive rock or a brilliant marble, an opaque gypsum or a translucent alabaster.

Common Limestone.

Limestones fit for building and agricultural purposes are found in every formation, from the oldest to those of the most recent origin. The rock is generally dug in open quarries, but occasionally, when it dips rapidly, and is worth the expense, it is followed downward by mining-the greater part of the stratum being excavated, and only portions left at intervals to support the superincumbent material. It is then broken into fragments of moderate size, and conveyed to a kiln, where, being placed in alternate layers with coal or turf, it is roasted, thereby expelling its water and carbonic acid. In this state it is known as shell or unslaked lime, and requires to be drenched with water to convert it into a powdery quicklime. As quicklime, it is used by the farmer; but it requires to be further slaked and mingled with a certain proportion of good sharp sand to

render it suitable for mortar. Besides building tural purposes, a large quantity of lime is used

soap-making, leather-dressing, dyeing, medicine,

and agricul

as a flux in

pur

Con

and in many

metallurgic processes, such strata being sought for this pose as contain but a small per centage of impurities. siderable quantities are also used in the purification of gas, L other economical processes. The supply of limestone in our foot to one hundred feet in thickness; the mountain or carboniown country is inexhaustible; it is worked in beds from one ferous limestone which underlies the coal-formation often ex. ceeding that thickness, and ranging unbroken for many miles in

extent.

Marble.

whether studded with the strange forms of fossils,

lime, containing only a few subordinate impurities,

or streaked

which do no

Marble is but a technical term for any species of limestone sufficiently pure and compact to be susceptible of a fine polished surface. No matter what the colour, whether white or black, Iwith the most fantastic veinings, marble is but a carbonate of more than affect its colours and markings. The best varieties are obtained from the primary and transition formations, in which with party-coloured veinings. Pretty enough marbles for slabs Iwith the shells, encrinites, and other corals which are imbedded secondary formations, these being, in general, curiously marked and other architectural purposes are sometimes obtained from the degree of polish as the primary marbles, some of which, like that None of these, however, are susceptible of the same extent have varieties of native marbles, which, though inferior to

in the mass.

of Carrara, seems almost translucent. Most

countries of any

those of Italy and the Archipelago, might still be m

ore extensively

used than they are, were it not for the expense in cutting and

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VERYTHING we enjoy, as food or clothing-every substance we employ for the purposes of life, whether useful or ornamental-is derived from the earth, or the earth's productions. Be the products animal or vegetable, mineral or metallic, they are alike gifts from the same source; though, in respect of their origin and position, the latter may be more strictly regarded as the "treasures" of that solid or stony portion which is accessible to man. In this sense we intend to devote the present sheet to the more important minerals, describing their nature, origin, and uses, and presenting such particulars respecting their commercial history as may seem interesting to the general reader.

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For the more accurate comprehension of the subject, it may necessary to premise that we speak of the crust of the earthmeaning thereby that superficial rind or portion accessible to human investigation in contradistinction to the interior masses, concerning the nature of which we can only form conjectures. In this crust the rocky substances are variously arranged: some are found in layers or strata-hence said to be stratified; others appear in vast irregular masses, presenting no trace of bed or layer, and are accordingly termed unstratified. The matter of the stratified has evidently been deposited from water, and from this view of their origin, they are generally known as aqueous

No. 130.

or sedimentary rocks; while the unstratified, presenting no appearance of deposit, but everywhere an irregular configuration, and, moreover, often breaking through and contorting the strati fied, are considered of igneous or volcanic origin. Both sedimentary and igneous rocks present various mineralogical and chemical characters: thus, of the former, we have roofing-slate, sandstone, coal, limestone, &c.; of the latter, granite, basalt, and lava all very distinct in composition and appearance. Besides differences in mineral composition, the sedimentary rocks contain different kinds of fossils—that is, the petrified remains of animals and plants; and such distinctions have rendered it necessary to arrange the rocks constituting the crust of our globe into various formations-meaning by a formation any suite of rocks possessing some peculiar mineral or fossil character. Thus we speak of the "coal formation," meaning thereby not merely the beds or layers of coal, but the sandstones, shales, ironstones, and the like, which alternate with and accompany that mineral-seeing that the whole have been evidently deposited under similar conditions, and that the same kinds of plants and animals are found fossil within them. Deviating in some degree from the usual technical arrangements, we shall describe the various mineral treasures of the earth under such heads as appear best calculated to aid the comprehension of the ordinary inquirer.

BITUMINOUS SUBSTANCES.

Bitumen-from a Greek word signifying the pitch-tree-may be regarded as embracing all those inflammable mineral substances which, like pitch, burn with flame in the open air. Naphtha, petroleum, and asphalte are familiar examples; but all substances impregnated with these bitumens are said to be bituminous. Hence under this head may be included coal in all its varieties, as well as bituminous slate, slaggy mineral pitch, and the asphaltes of commerce.

Coal.

Coal, of which there are several distinct varieties, is one of the most important minerals with which man has yet become acquainted. By it he fuses the metals, produces steam which sets machinery in motion, prepares gas for light, heats his apartments, cooks his food, and, in short, renders all the resources of nature fit for civilised use. It is uncertain when coal first began to be used in Britain as fuel, but in all probability it was not earlier than the beginning of the twelfth century. In 1281, Newcastle is noticed as having some trade in that article; and a little later, we find it mentioned in the Chartulary of the Abbey of Dunfermline. In the reign of Edward I., its use in London was prohibited, in consequence of the supposed injurious influences of the smoke; and this prohibition we find renewed at several subsequent periods; but all to no purpose. The increas

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