CHA P. II.

Of the different kinds of Lodes in respect of the Earth and Stones they contain.

T

HE contents of our Fiffures are very complicated, and obtain their several diftinct appellations from the nature and appearance of the most predominant Earth, Clay, Stone, or Mineral, contained in them; without any .refpect to the metallick impregnations of Tin, Copper, or Lead, unless the Ores of thofe Metals are very rich, and more abundant, than all the other contents of their Fiffures. The fame Lode, at higher or inferior levels, fhall be alternately named a Goffan, Mundick, or Flookany Lode, purfuant to their predominancy at twenty, forty, or fixty fathoms depth; or any other intermediate level they may offer to the obfervation of the Miners. Upon this account, moft Lodes take their names from the kind of Stone or Mineral they most abound with, which often participates very largely of the nature of the Strata enclosing them.

The generality of our Lodes are very different to the eye and in their impregnation, near the furface, from what we find them when deeply funk upon; and though it has been known, that the backs of fome few veins have proved very rich, yet they do not always hold Metal, and frequently they do not carry Tin or Copper Ore enough to pay the charge of drefling or cleanfing them: nevertheless, in the finking upon fuch veins, we hope they will depart from their primary colour and appearance, and form large bodies of Tin or Copper Ore.

The flight metallick impregnations of our Lodes, which, especially in Copper, are generally obferved to fifteen, and even thirty fathoms deep, muft certainly arise from the scarcity of faline mineralick principles, which the water so near the surface cannot be largely faturated with; and having lefs depth of Strata to receive the metallick folutions from, they of neceffity cannot be furnished with ftrong menftrua, to act upon the Lodes, or depofite themselves. Although Mines are seldom discovered rich upon the backs, we prefume for the reasons before given; yet experience will inform us, that they are fometimes well ftored with Copper and Tin Ores of the richest quality near the

day

day or furface; but this more frequent in the latter, though of no long continuance.

We shall divide Lodes which carry Tin, Copper, and Lead, into twelve different kinds, in regard to their foreign Materials; and the removes visible in them, we fhall clafs into their proper fubdivifions. The Lodes are ranged in the following order:

I.

Of all thefe Lodes, the Goffan is moft common; and is ever difpofed to yield Tin and Copper, if it runs east and weft; but those of a contrary direction, in respect of those Metals, are fteril and worthlefs. Goffan may not improperly be divided into five forts: viz. 1. a Tender Red Goffan; 2. a Tender Brown Goffan; 3. a Dry Pale Yellow Goffan; 4. a Poor Tin Goffan; and 5. a Gal or Gally Goffan: all of which are ochreish fubftances, of a rufty ferruginous complexion, being mostly Earth and Crystal coloured by Iron, with frequently no inconfiderable portion of that Metal.

I. The Tender Red Goffan is very much inclined to produce Copper Ore, especially if the Goffan be fpungy, cellular, and of a very red colour, like to a well burnt brick. When it is thus, and spotted, or tinctured with green Copper Ore, like pieces of Verdigreafe, it does not often deceive the proprietors. So, likewife, Stones of blue or black Copper Ore, or of yellow Ore having a black or purple outside, are very hopeful to follow when mixed in this Goffan. Yet the Ore in this nidus is bunchy and uncertain, till proved to fome tolerable depth. But if Stones of Lead Ore be found in this Goffan, it promises well to produce a good quantity of Lead. This kind of Goffan was upon the back of Pednandrea Lode, and fome parts of Huel Sparnon, and is now very plentifully to be rifen at Michell's Goffan Mine, in Redruth.

2. A tender Brown Goffan, much of the colour of Iron, very brittle, and full of holes. The smaller particles of it are of a brownish yellow, very crumbling, and fall to duft by long exposure

expofure to the air. It is this Goffan which backs the Huel Virgins in Gwenap.

3. A Pale Yellow Dry Gossan, of a hard crystalline intermixture. This fort of Goffan fometimes yields Copper Ore, yet feldom turns to any great account. However, I believe it to be more promifing for Lead than Tin or Copper, as I have obferved it to produce that Metal in Nanfkuke Downs and elsewhere. This must be most like the Goffan of Hernn Groundt Copper Mine in Hungary, the mother of which Ore is yellow, fays Dr. Brown, Philos. Tranf. 59.

4. A Poor Tin Goffan, implies that which is fo in refpect of its yielding Tin; for otherwise, it may be kindly enough for Copper. This Goffan fometimes will yield a very tolerable profit, on account of its cheap and speedy working for Tin. If it is red and brittle, it is a good indication of Copper Ore in depth, as the Tin leffens and wears out; and if it is tinctured with Verdigrease, it is very hopeful indeed. Formerly, a notion prevailed, that every Goffan which did not produce Tin upon the backs, was not worth the attention of the concerned for Copper; but it was a vulgar error derived from father to son, in times when Copper was very little known. Huel Virgin, and other great Copper Mines, have proved, that Goffans not productive of Tin, will yield abundance of Copper.

5. A Gal, (Kal) or Gally Goffan, is of a hard compact nature; its colour blacker than the other Goffans, and more like rufty black Iron. This makes Tin; but it very seldom anfwers for Copper, unless it changes to tender and brittle. This Goffan contains fo much Iron, that it sometimes ought to be ranked as an Ore of that Metal: I have been informed by my friend Mr. Bennallack, that he has affayed fome Stones of this Gal, which have produced three-fifths of their weight, good Iron; but this is feldom found in confiderable quantities, and its different Lodes are impregnated therewith, from this large to an exceeding small proportion.

Though all these Goffans have an intermixture of each fort, yet that which is most abundant, gives the Lode its denomination. A tincture like Verdigrease is not to be rejected in any of them, for it is very promifing for Copper.

II. A Peach or Peachy Lode, takes its name from a kind of Stone which principally abounds in the Lode, and is generally of a fpungy texture, and of a greenish or dark green olive colour. It is better for Tin than Copper; but is not a desirable Lode for either, especially the latter, which is always of a poor quality and value when found in a Peachy Lode.

III. A Scovan Lode, is formed of a hard compact cryftalline Stone, either of a brown or black hue, according to the colour of the Tin with which it is mixed. The Ore is often rich, ponderous, and folid in this Stone; and when it is worth one half for Metal, they call it Scove. The Lode is ufually very small, from the breadth of four inches to fourteen; the latter is thought to be a tolerable fize; and, notwithstanding its folidity and demand for gunpowder to blaft it, will yield much profit to the adventurers under other favourable circumftances. Sometimes this Scovan Tin lies in a lefs folid Lode, as to the Lode itself, which is cavernous, and full of holes, thence called a Sucked Stone by the Tinners, as if all the heterogeneous matter had been fucked or rather washed out of the Stone, and nothing was left behind but pure folid Tin Ore. This fucked Scovan Lode is larger when it occurs, even to fome feet in breadth; and fo is the folid Lode likewife at times.

IV. A Caple Lode. The Scovan Lode, when in decay for Tin, will commonly degenerate into a Caple; which, in fact, is mostly of the nature of a Scovan Lode's walls, or that enclofing Stratum, which it is in contact with; thence called the Caples, or walls of the Lode. But there is really fuch a thing as an original Caple Lode, properly fo called; which abounds. with a very stiff hard Stone, fomething like a Limestone, except the colour ; wherein the Tin is fometimes veined, and other times very small and diffeminate. A primary Caple Lode is promifing for Tin, though but seldom fo for Copper; unless there is a branch of Copper Ore or Goffan, that runs downwards in the Lode: if this Caple chances to hit into a body of Copper Ore, it commonly makes a durable Mine though the Ore is none of the richeft.

V. A Pryan Lode, is fo named, not in refpect of any peculiar quality of the Earth or Stone, any further than barely that it lies in the vein, in an arenaceous pebbly state, with small Stones of Ore intermixed, and not in large rocks or Stones; in which sense, a Goffan, Flookan, Mundick, or any other Lode,

may

may be called a Pryan Lode. and apt to yield Tin of the pureft metallick quality. The Lode is often fo very lax and fandy, that it will run against the workmen like a fand bank; and the man who handles his fhovel beft, is preferable to a Pick-man. If the walls of the Lode are tender likewife, it requires much timber to bind and keep open the workings. When Copper Ore is Pryany, it comes to grafs very cheap and speedily, and produces a quick profit.

This fort of Lode is very tender,

VI. A Quartz Lode, or Rampant Spar Lode, vulgarly fo called, is placed by fome among the Goffans, though I do not fee for what reason; this being a hard unmetallick petrifaction, thence called a Spar Lode by those unacquainted with real Spar. There is no Lode totally exempt from this Stone; and many branchy veins of it are to be feen throughout all our ftrata, unmixed with any other matter. In the grofs here fpoken of, it is a hard, opaque, yellow, or white cryftalline exudation, from the adjoining Crystal rock.

VII. A Crystal Lode. Quartz is undoubtedly the most debafed kind of Crystal; yet with regard to Crystal Lodes, I can from experimental knowledge make four other diftinctions, whereby their good or evil tendency for Tin or Copper, will more evidently appear.

I. The first is a greyish white, dull, hard, opaque, and rocky Crystal, which produces no Metal in itself, or in those Lodes which degenerate into its kind; for even if there are fome Stones of Ore found in other Lodes, yet where this comes in, it is a certain prognoftick of fterility and decay. It is moft natural to Tin Lodes at a great depth.

2. A smutty black, or black grey Crystal, is a very unlikely appearance for Copper Ore. It occurs but feldom; and when it does, it betokens a very fudden decay, though the Lode was fruitful before.

3. A brown candied, or amber coloured Cryftal. This is small, tender, and very like brown fugar candy. I take it to be hopeful for Copper; and it mostly abounds with a black Pryany Copper Ore, which laft confiftence it imparts from its arenaceous property. This wears out in finking, and the Lode generally changes to a yellow Ore, and folid Stone.