BOOK II.

СНАР. І.

Of the Strata of the Earth, and the Fiffures in which Metals are found, their Direction, Inclination, or Underlie.

EFORE we difcover the receffes of our Metals and

BEM

Minerals, it will be convenient for the reader to have fome knowledge and acquaintance with the circumjacent Strata, which enclose the objects of our enquiry: purfuant, therefore, to the plan of a late ingenious author, upon our entrance on the fubject before us, we will examine the shell firft, and then con

fider the kernel.

The Strata of different countries are various; and from enquiry I cannot find that they are influenced by the atmosphere or climate in any degree: and they are not only various, but alternate in their extent, breadth, and depth, in all parts of the world. In the Mining countries, they are found of different denfities and gravity, Stratum fuper Stratum throughout; fome hard, fome soft, then hard and foft again. Thus we may find uppermoft, a Stratum of Granite, or Moorftone-rock; then a fofter Granite, called Grouan; now Kellas; and fo on, to the concave of the grand abyfs. Half a mile distant, the layers of Rock or Stone will be altogether changed in their pofitions or complexions; whereby no abfolute rule can be formed, to decide upon the certainty of meeting with this or that Stratum, before the industrious Miner has laid them open to view.

I fhall not attempt to defcribe all the Strata that are to be met with; but shall confine myself to Cornwall, and even that part of it which is difpofed for Metal, within compass of my own perfonal infpection.

The general law of attraction evidently appears in the diftribution of our Strata; and their fpecifick gravities seem not to determine them fo much as might be expected: whence we

may

may argue, that when folids and fluids formed, (and from a ftate of chaos became divided into diftinct bodies) the parts of the former being deferted by the latter, muft needs grow closer together. But the maffes of Earth, Stone, and Clay, were not at this time merely paffive; they formed larger and more compact bodies, every where, according to the mutual attraction of their fimilar parts within proper distance. It must be further obferved, that as all fimilar parts struggled to come into contact with each other, fo at the fame time they deferted, repelled, and expreffed all diffimilar and contending particles; confequently, maffes of different natured particles, feceded and fled from each other, every party (if I may be allowed the expreffion) tending to unite and combine with its like. Dr. Worthington, in his Scripture Theory of the Earth, fays, "All matter gravitates towards all matter; fo all homogeneous parts of matter gravitate ftill more powerfully towards each "other, whereby they are more clofely united and compacted

together, according to their specifick textures. Each there"fore will affort themfelves, and affemble with their kinds "refpectively." Thefe caufes then, viz. the defcrtion of moifture, the union of fimilar, and the mutual repulse of diffimilar particles, must all have contributed to form the maffes of our terraqueous globe into fuch separate portions as we now find them in. This accounts for the diverfe diftribution of our Strata, which by this theory will not be founded upon chance or cafualty, as was the cafe by Mr. Hawkfbee's return to the Philofophical Society in the year 1712, when he bored to the depth of thirty Strata of a coal pit.

However, in the natural class and order of our Strata, I shall make my obfervations in proportion to their hardness and folidity, beginning with the tenderest first.

Soft Grouan, though a Stratum, can scarcely be called a Stone; for it is rather a fandy or priany Stratum of Moorstone gravel, not cemented together, but lax, arenaceous, and mixed with dispersed Stones of Granite. It generally lies at the extremities of the Moorftone Stratum, or hard Grouan. In some places it is fo fair or foft, as to run out against the workmen, and requires a great deal of timber to fecure it; but notwithftanding this, it enclofes numbers of Tin Lodes of confiderable value in the parishes of Wendron, Camborn, Crowan, Redruth, Gwenap, Illugan, &c.

Slate is common to many parts of our county; but, in quality of Slate, is not difpofed to fecerne Mineral juices, although fome thin efflorefcencies of Mundick have been feen on the

edges of the famous Delabole Slate-ftones. The Slate, or Shelfy-ftone, is always uppermoft next the loamy foil; but, in depth, it enters into the nature and consistence of real Killas.

Of Killas I have obferved fix forts common to us, the white, the red, the yellow, the brown, the cinereous or bluish, and the deep blue. The firft is very white and tender, and from its exceeding tenderness is called Fair Ground; it requires much timber and boards for binding, and fecuring it from filling the Mine, and endangering the workmen's lives. The red is not fo fair, but is well difpofed for Copper, or Tin Lodes; the latter preferably. The yellow is but indifferently difpofed for either. The brown, which has various fhades of lighter and deeper colours, is generally a hard Stone, and contains Lodes of Tin more commonly than Copper. But of all the Killas, the cinereous or pale blue is most desirable, as the enclosing Stratum of a Copper Lode. We find it the most common and agreeable cheft that encloses our cabinets of jewels. Conftant experience will incline us to give this Stratum the preference to all others for Copper Mines, on account of its generally accompanying a rich Mine; and because it is tender and agreeable to work upon in the finking of fhafts and the driving of drifts or adits out of the Lode. It is this kind of Killas which we call Feafible Ground, i. e. to be easily broken, and yet firm enough to stand without the support of binding with timber and boards. However this will oftentimes, by infenfible degrees, wear out as we call it, and become a deep blue, hard, unkindly, and coftly Killas, neither favourable to the Mine nor the labourer. It will require great addrefs, and much gunpowder fometimes, to break and make way through it. A Killas in its beft ftate, is foft, tender, fleaky, and fatty; will cut to any form underground, and requires no timber; but if it is hard and untractable, and works in very small fhreds of Stone, it is unfavourable to work or enclose Metal.

Elvan, at a fhallow level, is a gritty kind of Stone, most like a coarse Freestone, but in depth is exceeding hard. The two most common colours of this Stone are a bluish grey and a yellow Freeftone. It commonly yields great quantities of water; and we take it to be of the fame kind with that Stone which lies on the Culm veins in Wales. It fometimes runs in a direc

tion north, and fouth, contrary to the metallick veins, which generally keep their courfe through it, but the Lodes are frequently fqueezed up by its accompanying them fome length in their course, or are split into many small branches. Sometimes the Fiffures or Lodes are thrown fhort on one fide, out of their direct course as it were, by the extreme hardness of this Stratum, and afterwards they recover their course again. At other times the metallick veins are elevated or depreffed by it, though they always recover their former direction, and unite again; for this Stratum wears out at a great depth, and is fucceeded by Killas.

Moorftone or Granite. The name of Granite, which these Strata have univerfally obtained, is a modern name given them by the Italian writers, on account of their being concreted into grains, or in a granulous structure, and not compact and uniform as the Marbles, &c. are; thence Granita i. e. è granis compofita. The parts of Granite are not homogeneous, but are different concretions of Quartz and Micæ. The varieties are composed of black and white Talc, a dead earth not unlike the white Boles or Pipe Clay, and true Crystal.

We have five forts common to us, viz. the white, the dove coloured, the yellow, the red or Oriental Granite, and the black or true Cornifh N° 1 of Hill. Either of these as a Stratum, is called a Hard Grouan Country, (in the Swedish tongue Graberg, and Graften) and the two laft are frequently so hard and invincible as to tire the patience and pocket of the adventurers, and the labour of the workmen. Grouan Strata are disposed for Tin, which in fuch fituations is generally of a rich quality, or cannot long be fought after or wrought in its almoft impregnable walls. They are feldom likely for Copper Ore ; and were long thought to be wholly adverse to that Mineral, till the great Mine of Trefavean proved that rule exceptionable.

The Ire-stone, or Iron-ftone, is by much the hardest of all Strata, and borrows this name from its extreme hardness, and not because it contains Iron. It is of a dark bluish colour, like Lead that has been long exposed to the weather; and usually fo hard, that it must be wrought with Steel borers, and then blown by gunpowder. It often keeps a courfe eaft and weft like a Lode, but is commonly very wide; and therefore it is very tedious and chargeable, where an adit must be driven across through it. It is this Stratum that is uppermost through great

part

part of the middle of Camborn and Illugan parishes, where many principal Copper Mines are enclosed in it. Tin Lodes are very feldom found in Ire-ftone, but very rich Copper Lodes in many places are natural to this Stratum or country. We do not obferve that it ever gets into the Lodes themselves, although there are fome dark hard peachy Stones very like it in fome Lodes. The author of a familiar difcourfe concerning the Mine adventure, fays, "It is a conftant obfervation amongst all "Miners, that the harder the rock, the richer the Mine; na"ture generally makes the cafe ftronger or weaker, according "to the richnefs of the treasure therein contained: for where"ever the fides of a vein are cracked and broken, the mineral "water that feeds the vein, runs off, and the vein proves dead

or very poor but when the fides of a vein are folid and firm "without cracks, the mineral feeder impregnates and enriches "the Mine, and the fame proves quick and rich in Ore." This cannot be a general rule, for our theory and observation prove its falfity. It cannot depend upon the confinement of mineral water in one particular place, that a Lode shall be rich in Metal, so much as upon the strength and peculiar attraction of the nidus through which it circulates; for we conceive the attraction to be instantaneous: therefore, water charged with mineral falts or particles continually paffing through a vein, will more abundantly impregnate that vein, than if its principles are decompofed, and the water is left pure and unmixed. This is the reasoning of moft experienced Miners; for when a rich Lode of Copper, &c. is cut with abundance of water following the discovery, they always declare, "It is a very promifing "circumftance."

The foregoing Strata are only common to Tin and Copper Lodes in this county, and if we have not specified more which may be thought of by the difcerning Miner, we will nevertheless take upon us to fay, any others that may be mentioned will only prove to be varieties of fome of these. We cannot learn, that there are either Chalk, Marble, or Limestone, in any part of our mining Strata; confequently real Spar is foreign to our country.

Now when the general affimilation of kindred particles happened, and folid bodies were feparated from fluid; between the diffimilar, certain cracks, chinks, and Fiffures, in various directions and contortions, were effected at their extreme angles; but as the matter of each Stratum became more compact and

denfe