of fuch humidity with the dry terrene, divers and various Stones are produced.

The particular circumstances which attend the formation of Stones, vary the effect of these general principles divers ways. For inftance, if a portion of this juice, diluted in Water, happens to be furrounded with earth, and the juice be not in quantity fufficient to petrify the whole earth as faft as the Water evaporates; there will arise a mass partly crystalline and tranfparent, and partly opaque, diffimilar, and earthy and fuch we prefume is the difference of the Caples of our Lodes, and the contiguous ftrata; the former being fometimes more compact and firm by its contiguity to the juice percolating the vein, and the latter less so, by its proportional distance from the Lode If the fame Crystalline juice be in the middle of the mass, only the middle will have a Crystalline appearance and firmness; fuch as the huge rocks of Crystal (Quartz) we often fee rife out of a vein or lode, which commonly implies a failure of Metal in that of a Mine.

part

This Cement may be divided into three degrees of purity: the first a coarse Quartz, which is the most impure, and covets no particular form; the fecond is Cryftal, which forms hexagonal columns, cufpides, and pyramids, and is the connecting bafis of Slate, Killas, Granite, or Moorftone, &c. But if by a ftill greater degree of purity, the Stone becomes fpecifically heavier, of better luftre, and refifts fire almoft to immutability, then it is called a Diamond; and the Ruby, Sapphire, Amethyft, &c. are but this Diamond tinged and reduced, as to luftre and hardness, by fome metalline tint.

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What is vulgarly called Spar with us, and which is fo plentifully scattered the furface of every heathy common, is not the real Spar; and is, by moft Lithologists, better known by the German name of Quartz, for want of a proper English appellative. Spar, by itself clear and unmixed, is very rarely found in this county. Indeed, the reason of its scarcity is, because we have little or no calcarious ftrata to produce it. The late Sir John Hill, in his history of Spar, which he divides into eighty-nine fpecies, fays, that Limestone is only coloured hardened Chalk, and Marble is the fame. Marble is a purer Limestone, and Limestone a courfer Marble. Water being faturated with the principles of Sulphur, and with Chalk, keeps on its gradual course horizontally through the lime rock,

till it meets a fiffure, a perpendicular crack or opening, dividing one part of the rock from another. Here it ouzes forth; and meeting with a lighter air, fufpends and evaporates flowly.

We have faid before, that flow evaporation, and perfect reft, are the requifites of Cryftallization. The Sulphur and pure Chalk thus united, form one folid body; which crystallizing gradually, fometimes appear in regular rhomboidal particles and is the fubftance properly called Spar. That the Spar formed in the fiffures of rocks, is thus washed out of Limestone itself, is certain; because none but Limestone rocks have Spar in their fiffures. Rocks of a Crystalline matter, or formed of a vitrifiable Stone, have always Crystal, but never Spar, in their cracks or fiffures. It grows continually; for wherefoever there is a crack in a Limestone rock, new or old, Spar always fills, and overruns the furface. Therefore the calcaricus nature of Spar, is of its effence; and no form, nor all the other characters in the world, could conftitute any production a Spar, that wanted this. It always ferments with acids, and burns to lime.

The formation of Spar is yet a fubject of enquiry. Its atoms are all Spar; each particle, into which we can without violence divide it, is the fame in all refpects as the whole and as the Foffil world admits of no generation by egg or feed, it seems moft probable, that all the variety of forms, in which we behold this Protean Mineral, are owing to no cause but the arrangement of rhombs, into as many forms as they are capable of producing. It fills the cracks of its own rocks, and of no other; for Crystal columns rise from Crystalline rocks; and from Metalline maffes fractured grows Mundick; each separated from the great mixed body we fee fplit, and each formed into figures by its own laws.

The obvious scarcity of Spar in this county, is abfolutely proved in the almost total absence of Limestone, whence it is mineralized; neither have we yet feen a perfect Sparry Rhomb in Cornwall.

It may be difficult to perfuade the vulgar Cornish, that we have little or no Spar in our Mines; but that so it is, every unprejudiced obferver may be convinced by the teftimony of his own fenfes. They denominate every fpecies of Quartz and Crystal indifcriminately, except the Pfeudo-Adamantes, Spar; fo that in their opinion almost all the streets in the county are

paved with Spar inftead of Quartz; and with them every Crystalline rock under-ground bears the fame name. It is time, however, that this confufion and mifnomer of Foffils should be abolished, and fuch mistakes and falfe diftinctions laid afide for the fake of order and propriety. Be it, therefore, henceforth remembered, that all those masses of white and yellowish Stones scattered upon the furface of our lanes and commons, which are only used for paving and hedging, are Quartz, and have no Spar in them. If they were truly of a Sparry texture, they would fave us much expence and labour for Limestone, which is now imported from Wales and Devonshire; befides the cheap and ready manure they would afford, for the cultivation of our land.

Plain Crystal hardens into any figure, of which its own gravity, and the matter in which it forms, will admit; and we find it veined in all our Killas, Caple, and every part of our ftrata, that is generally and vulgarly denominated the Country by our Tinners; yet it is perfect Crystal, breaks irregularly, yields fire plentifully, is very hard to the graver, and will not ferment with Aqua Fortis. It will fometimes form itself in hexagonal opaque columns, cufpides, and pyramids, of an uncommon large fize, but of no value.

But if those pyramids are of a fine pellucid Water, they become the Pfeudo-Adamantes of the purer kind, and are thence eminently called Cornifh Diamonds; and are by Dr. Grew, and others, reckoned fuperior to the Bristol Stone, and every other diaphanous Crystallization in Great-Britain.

CHA P. III.

Of Metals and Minerals, and the Fluxes for affaying them.

HE inferior Metals, especially Copper and Iron, are the easiest of any to be diffolved by moft acid menstrua, their parts being very different, unequal, and heterogeneous in themselves, and more fufceptible of any outward force or impreffion. We take this to be the cause, why these two Metals are more fubject than others to be corroded and injured by exposure to the air, which abounds with volatile acid falts, and

thereby becomes a menftruum, that readily adheres to, refolves, and corrupts thofe tender imperfect Metals; whereas Gold and Silver, whofe parts are moft folid, denfe, and homogeneous, receive little or no damage by contact of the acid falts. Lead and Tin likewise, not being eafily refolvable by Aqua Fortis or any water of that kind, are not near fo foon prejudiced by the faline pungent particles of air, as Copper and Iron are; which probably happens, because they have a greater degree of fimilarity of parts better united; or becaufe they contain fomewhat that approaches to the nature of Sulphur, whofe property it is to refift all acid menftrua.

The word Ore, as alfo the word Mineral, in the largest acceptation, comprehends any impure Concrete or Fofil, that contains either a Metal, Semi-metal, or Mineral juice; but if the fpecies of the thing fignified, be added to the word, then the particular fenfe or meaning of the expreffion is limited and denoted. Thus it is ufual to fay Copper Ore, Lead Ore, &c. The Ore of Antimony, The Minerals of Copper, of Lead, and the like; fo that the words Ore, and Mineral, are only fynonymous terms, that imply any kind of Mineral Foffil without expreffing its nature. Nevertheless, a barren Mineral Foffil, which yields no produce in the fire, cannot well be termed an Ore, though it is called a Mineral; for it is improper to fay, the Ore of Mundick, &c. Custom however prevails fo much in the terms of our Miners, that they often call fuch Minerals as they know are of no value, by the name of Ores; and, therefore, to be more clearly understood in what follows, by the word Ore, I mean only a Foffil or Concrete, which produces real Metal, as Gold, Silver, Copper, Tin, Lead, Iron, and alfo Quickfilver; by the word Mineral, I confine myself to the more crude Foffils or Concretes, which yield Sulphur, Vitriol, and other fuch brittle bodies; and by the word Semi-metal, I mean Antimony, Bifmuth, and Cobalt. I prefume it neceffary to make this distinction, to prevent the perplexity in which those who are but little acquainted with the fcience of Metals, are often involved.

All things in the bowels of the earth, which occur to the confideration of a Mineralift, are reducible to the following claffes firft, Earths and Stones; fecondly, Concrete Infpiffated Juices or Bitumens, as alfo thofe which are liquid; thirdly, Semi-metals; and fourthly, Metals. and fourthly, Metals. We shall speak of each of these in their proper order.

First, of Earths; of which there are many forts of different colours and natures, whether fimple, or compound; and are to be esteemed among Ores or Metals, no further than with regard to the plenty or fcarcity of Metals or Minerals they feem to indicate; or else as indications which may be the best method to extract the Metal that is intermixed with them: but I shall not here profecute the inquiry into this fubject, because I fhall have occasion to take particular notice of it hereafter.

We shall likewise fay nothing of many remarkable Earths and Boles, as they have little or no connexion with Mines or Metals; fuch as Bole Armoniack, Terra Lemnia, Fuller's Earth, Lac Lunæ, Spanish Bole and Terra Sigillata, except the Steatites or Soap Stone, which is in fuch plenty, and fo diverfified and beautiful, at the Lizard Point, as to have invited many Foflilifts to infpect its fituation, colours, quantity, and properties. The varieties of this Foffil, at the Lizard only, are divided by Dr. Borlafe into ten, whofe No. 1 which is the Steatites quæ paratonium antiquorum, No. 13 of Da Cofta, and the argella albiffima ponderofa tenax p. 17 of Hill, is found in veins about two fingers breadth at Gew-Grez cove, where it is carefully felected from the other forts, barrelled up, and almost wholly engroffed by people employed under the managers of the Porcelain Manufactories. But the No. 14 of Da Cofta, which he defcribes as taken by himself from our foap rock, he eminently denominates Steatites vera; which I think he ought to have ftiled the Steatites Cornubiæ, as he recommends it to the China manufactories lately established in this kingdom, and doubts not but we shall be able to furpass the manufactories of all other European nations, fince none have thofe Steatitiæ in fuch plenty and fo fine. It is remarkable, that letters written with Soap-ftone upon glafs, though infenfibly fixed, are not to be moved by washing, but always appear upon being moiftened by the breath.

The curious memoir in the tranfactions of the Royal Academy of Sciences at Paris, for 1727, communicated by the learned and indefatigable Monfieur de Reaumur, fully informs us of the art of making Porcelain, and the true fubftances used for that purpose by the Chinese he has in that memoir judiciously confidered China as a Semi-vitrification, and on the principles of burning the ware to that exact ftate, he has established the perfection of the art. Now as all Earths vitrify, it is evident no true Porcelain can be made only of Clays, but other necef

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