ftance in which it mineralized any metal; but the appearance of that fpecimen was influenced by the addition of iron.

To the clafs of earths are added two appendices, together with a chapter on animal and vegetable earths. The first appendix is on the diamond and plumbago. The diamond is inferted by Bergman, among the inflammables; but our author objects to this arrangement, becaufe its inflammability is fo obfcure. Certainly no ufeful purpofe is answered by ftyling it inflammable, yet it is adapted to no other clafs, for it leaves no refiduum. The plumbago refembles the molybdæna, and is undoubtedly metallic, though the ufual fluxes have not hitherto been found capable of reducing it. One hundred grains of this fubftance contain thirty-three grains of aerial acid, and fixty-feven of phlogiston. It is probably neceffary to add a larger quantity of the acid in which the ufual fluxes are deficient. The acid of molybdæna is of a very peculiar nature; like the phosphoric, it appears in the form of a whitish calx: we shall transcribe its properties, from Mr. Kirwan's work.

This acid is soluble in 570 times its weight of water in the temperature of 60; the folution reddens that of litmus, precipitates fulphur from the folution of liver of fulphur, &c. the fpecific gravity of the dry acid is 3,460. 3 Bergm. 127.

This acid is precipitable from its folution in water by the Pruffian alkali, and alfo by tincture of galls the precipitate is reddish brown.

• If this acid be distilled with three times its weight of fulphur, it re-produces molybdena.

The folution of this acid in water unites to fixed alkalis, and forms cryftalizable falts; fo it does with calcareous earth, magnefia, and argill: thefe laft combinations are difficultly foluble; it acts alfo on the bafe metals, and with them affumes a bluish colour.

This folution precipitates filver, mercury, or lead from the nitrous acid, and lead from the marine, but not mercury.

It also precipitates barytes from the nitrous and marine acids, but no other earth. Molybdenous barofelenite is foluble in cold water.

This acid is itfelf foluble in the vitriolic acid with the affiftance of heat, and the folution is blue when cold, though colourless while hot; it is alfo foluble in the marine acid, but not in the nitrous.

'Molybdenous tartar and ammoniac precipitate all metals from their folutions by a double affinity. Gold, fublimate corrofive, zinc and manganese, are precipitated white; iron or tin from the marine acid brown; cobalt red; copper blue. Alum and calcareous earth white. Scheele Mem. Stock, 1778.

VOL. LVIII. Od. 1784.

This acid has been lately reduced by Mr. Hielm, but the properties of the regulus thus obtained are not yet published.'

The fecond appendix is on the general examination and analyfis of earths and ftones. The utility of this article muft be obvious. It is accurate and comprehenfive; but is incapable of abridgment. We fhall conclude our extracts of the nature of particular fubftances, by the defcription of the tungstein acid.

Its folution in water reddens that of litmus; with alkalis it forms crystalizable falts; with barytes calcareous earth, and magnesia infoluble compounds.

This folution is precipitated white by the Pruffian alkali, and the precipitate is foluble in water.

It precipitates the folutions of vitriols of iron, zinc, copper, and the nitrous folutions of filver, mercury and lead, and that of lead in marine acid; all these precipitates are white: the folution of tin in marine acid is precipitated blue, but the folutions of gold and fublimate corrofive are not altered by it.'

The folutions of chalk or alum are not altered by it, but that of barytes in the acetous acid is precipitated, and the precipitate is infoluble.'

Vegetable and animal earths have been hitherto confidered as of peculiar natures; but the former confists of almost every kind of earth, the basis of the laft is calcareous ; fometimes it contains a little felenite, and, in human bones, is combined with the phosphoric acid. Vegetable earth also contains a great variety of neutral falts: this was first attended to by Mr. Margraaf, and has fince been pursued by different chemifts. It contains alfo manganefe, which has been hitherto little known. The following extract is curious and useful.

"Manganese feems to be contained in the afhes of moft vegetables, and to it the blue or greenish colour of calcined vegetable alkali is owing. Thefe colours are generally attributed to the phlogiston of the alkali; but if fo, they fhould not be found in fixed nitre, as the nitrous acid fhould carry off, during its decompofition, all the phlogifton; yet this alkali is always greenish, fo that the colour feems to arife from the ashes of the charcoal with which the nitre was decompofed. If 3 parts of the alkali of tartar, 1 of fifted afhes, and of nitre be melted together, they form a dark green mafs, which being diffolved in water affords a beautiful green folution, and this being filtered, on the addition of a few drops of oil of vitriol, becomes red, and after a few days a brown powder is depofited, which has the properties of manganefe." Scheele 56 Mem. Stock. 1774, p. 189. The afhes of ferpyllum contain very little of it, thofe of trees contain moft. Ibid. 180.

There is ftill an useful part of the fubject which our author has very flightly mentioned, viz. the formation and decompofition

pofition of ftones. The first is almost entirely omitted, except fo far as the forms and appearances have been altered by fufion. He seems to have been perfuaded, by the observations of fir William Hamilton and others, that ftones may be decompounded by expofure to the air; but the decompofition of the harder granites is fo flow, that we now know an engraving on a stone of this kind, which has been entirely expofed for above a century, where the fharpness of the letters feems to be in no refpect diminished. This ftone is fo hard, that the workmen themselves prepare the tools for their work, and a pick, hardened with the utmost care by a common fmith, feems to yield as eafily as lead. All their own art is not fufficient to preferve them for many hours, without repair. The decompofition of lava is very different. The hornftone marl, and the argillaceous fchifti, are, according to Mr. Sauffure, the most common ingredients of lava; to these we may add the killas rock, which we have fometimes obferved to be the foundation on which a volcano has refted. It will be obvious then, that these may be decompofed with greater facility, according as the fufion has been lefs or more complete, or in other words, according to the nature of the ingredients. But there is another mode of decompofition which has not been hitherto confidered. The lefs compact lavas, which are cellular, and always near the furface, are often filled with calcareous earth, in confequence of water paffing through them. This earth is frequently very nearly pure, by having only a fmall proportion of fixed air; fo that when expofed, it swells and destroys the texture of the piece, which contained it. We have seen lava, which has not been dug above seven years, in this way, crumbled into ufeful earth. We leave our readers therefore to judge how precarious every calculation, respecting the age of the world, must be from the thickness of mould

over maffes of lava.

To the end of the metals are added, reflexions on the nature of cobalt, nichel, and manganefe.' Thefe have been afferted to be modifications of iron, or combinations of different kinds; and it is the object of this chapter to combat thefe opinions, which Mr. Kirwan feems to have executed fuccefsfully.

The geological observations are fometimes new, and always curious or entertaining. We fhall felect the obfervations on the primeveal mountains.

Among the primæval, thofe that confift of granite hold the first place. The highest mountains, and moft extenfive ridges in every part of the globe, are granitical. Thus the Alps and Pyrenees are the loftieft in Europe, and particularly fuch of

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them as confift of granite, the Altaifchan, Uralian and Caucafus in Afia, and the Andes in America. From them the greatest rivers derive their origin. The highest of them never contain metallic ores, but fome of the lower contain veins of copper or tin, as thofe of Saxony, Silefia, and Cornwall. The granitic ftones next the ore always abound in mica; petrefactions are never found in them..

Many of the granite mountains of Afia and America form large plat-forms at about half their height, from which feveral lofty fpires arife. No fuch plat-forms have been observed in the Alps or Pyrenees.

That the formation of these mountains preceded that of vegetables and animals, is justly inferred from their containing no organic remains, either in the form of petrifaction or impreffion, from their bulk, extenfion and connection, which feem too confiderable to be afcribed to fubfequent caufes, and from their use and neceffity for the production of rivers, without which it is hard to fuppofe that the world had existed at any period fince the creation of animals. Moft naturalifts are at prefent agreed that granites were formed by cryftalization. This operation probably took place after the formation of the atmosphere, (which in the hiftory of the creation is called the firmament) and the gradual excavation of the bed of the ocean; foon after which, it is faid, that by command of God (that is, by virtue of the laws of nature which he established) the dry land appeared; for by means of the evaporation of part of the waters into the atmosphere, and the gradual retreat of the remainder, the various fpecies of earths before diffolved or diffufed through this mighty mafs, were difpofed to coalefce, and among these the filiceous muft have been the firft, as they are the leaft foluble: but as they have an affinity to other earths with which they were mixed, fome of these must also have united with them in various proportions, and thus have formed in diftinct maffes the felt fpar, fhoerl and mica, which compofe the granite. Calcareous earth enters very fparingly into the compofition of this ftone; but as it is found in fhoerl, which is frequently a component part of granite, it follows that it must be one of the primitive earths, and not entirely derived . from marine exuviæ, as many imagine. Quartz can never be supposed to be a product of fire, for in a very low heat it burfts, cracks, and lofes its tranfparency, and in the highest we can produce, it is infufible; fo that in every effential point it is totally unlike to glafs to which fome have compared it. As granite contains earths of every genus, we may conclude that all the fimple earths are coeval with the creation. This obfervation does not preclude further refearches into their compofition; for though water undoubtedly dates from the creation, yet fome late experiments fhew it to be a compound: their fimplicity may be only relative to the prefent ftate of our knowlege.'

After

After mentioning their height, our author enquires into the Structure of mountains, which are divided into entire, stratified, and confufed. Each of thefe are defcribed with accuracy; and he next treats of volcanos.

These mountains are of all heights, fome fo low as 450 feet, as that in Tanna, but they generally form lofty fpires, internally fhaped like an inverted cone placed on a broader bafis. This cone is called the crater of the volcano, as through it the lava generally paffes, though fometimes it burfts from the fides, and even from the bottom of the mountain; sometimes the crater falls in and is effaced; fometimes in extinguished volcanoes it is filled with water, and forms those lakes that are obferved on the fummit of fome mountains.

Both the crater and bafis of many volcanic mountains confift of lava either intire or decompofed, nearly as low as the level of the fea, but they finally reft either upon granite, as the volcanos of Peru, or on shiftus, as the extinguished volcanos of Heffe and Bohemia, or on lime-ftone, as those of Silefia, the Vicentine Alps, and Vefuvius. The decompofed and undecompofed lavas form irregular ftrata that are never parallel to each other. No ore is found in these mountains, except iron, of which lava contains from 20 to 25 per cent. and fome detached fragments of copper, antimonial and arfenical ores.

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'If we confider the immenfe quantity of matter thrown up at different periods by volcanic mountains, without leffening their apparent bulk, we must conclude the feat of thefe fires to be feveral miles, perhaps hundreds of miles, below the level of the fea; and as iron makes from to of all thefe ejections, we may infer that the interior parts of the earth confift chiefly of this metal, its ores, or ftones that contain it, whose greater or leffer dephlogistication in different parts may be the cause of the variation of magnetic direction.'

It is perhaps this error, refpecting their height, which has occafioned them to be fo frequently overlooked. They are fometimes within two hundred feet of the level of the fea, and we have seen them within one hundred and thirty. The crater is indeed, in cultivated countries, commonly obliterated; but the hill may be diftinguifhed by various marks. They are feldom combined in a ridge, but are often fingle, almost equally abrupt on every fide. Their tops are commonly covered with a cellular stone, and, when they are dug into on any fide, the specific gravity of the ftone increases according to the depth: there are no regular veins, but various cracks in all directions, fometimes empty, but more frequently filled with calcareous matter; fometimes with a black powder which, when examined, appears to be a mass of chrystals, probably of a ferrugineous falt. These are only a few marks: we can-. pot enlarge on the subject, we wish only to direct the atten

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