Transactions of the Geological Society, 1st series, vol. 2/On the Veins of Cornwall
VI. On the Veins of Cornwall.
By William Phillips, Member of the Geological Society.
A Visit to the county of Cornwall in the year 1800, the inducements to which were the objects of mining and mineralogical inquiry, afforded me many opportunities of conversing with practical miners. The subject was new to me; and it was with considerable pleasure that I listened to the many striking and interesting facts detailed by men ever ready to communicate the information they possess, and whose minds, as repeated visits to the County have since confirmed to be their characteristic, are habitually disposed to industrious ingenuity. It may well be supposed that the foremost of these subjects was the nature and peculiarities of veins, or as they are technically termed, loads, or courses.[1] Having learned that the run, or direction of the regular metalliferous veins is about east and west, and that in some districts, the same vein is known actually to pass through several mines, it occurred to me, as being within possibility, that at least some veins might extend the whole length of the county; and that if the situations of such mines as were then working, or had lately been worked, were accurately described on a map, it might throw some light on the idea. With this view therefore, after visiting many of the mines, particularly those of the mining district of which Redruth may be said to be the centre, that object was accomplished by the assistance of some friends. The result by no means confirmed the idea in which it originated: for although it evinced that in the year 1800 there were about 120 mines in the county, either then working, or which had lately been worked, few of the east and west or metalliferous veins, from causes that will be explained in the following pages, have been explored, or even satisfactorily traced more than two or three miles. The map was however preserved merely with a view to private gratification; but several gentlemen, whose zeal for geological inquiry induced them to consider this attempt to shew the localities of mines as in some degree worthy of attention, urged my offering it to the notice of the Geological Society, accompanied by a memoir on the subject of the Veins of Cornwall.
The map not being of course adapted to the present state of the mines, nor even sufficiently exact in regard to their several localities at the time at which it was compiled, to meet the public eye, its publication is laid aside for the present, not however without expectation of its being given in some future volume of the Transactions, in the most accurate and satisfactory manner.
But the ascertaining of the local and relative situations of mines, though of unquestionable interest to the geologist, can only be regarded as a link in the chain of inquiry. In order to render its value complete, it should be accompanied by a memoir, or rather a comprehensive history of each mine and of its connexion with those immediately contiguous to it on the same veins. But this could only be attained by years of unceasing and laborious inquiry on the spot. In the counting-houses of the most successful mines the only information ever committed to paper, in regard to the workings of the veins are the expenditure and income, together with a section of the vein from which the profit is reaped, without a single notice in regard to the tract of country through which it passes. Of the generality of unsuccessful mines, which form by far the greater proportion, all that is registered is the loss or expenditure; other information can only be obtained by a recourse to personal inquiries of the conductors or captains.
The following pages are principally intended to exhibit an outline of general facts relative to the veins of Cornwall, arranged under separate heads. In drawing up this sketch, such advantage has been taken of what has already been published on the subject as seemed consistent with the present object, carefully rejecting every thing doubtful, or hypothetical, and having in constant view the advantage of corroborating every assertion to the extent of my limited information, by a recourse to the peculiar circumstances of individual veins or mines. Though thus limited in its object and extent, it will I trust be found both consistent with its intention and accurate in its detail; nor will its service be trifling if, upon a subject so interesting, and on which little is known, it should be the means of inducing some of the numerous and well-informed men, who are immediately concerned in mines, to gratify the increasing interest which is felt on geological subjects, by giving to the world occasional details of the many curious facts that almost daily occur in practical mining.
Almost every mine of any considerable depth or extent, is deserving of the notice of the geologist, because each has its peculiarities:—for when two or more mines are on the same vein or veins, there is frequently but little else that is common to each; and even in the same mine, situated beneath a few superficial acres, there is often a strange variety in the dimension, contents, and direction of its veins, and in the country[2] through which these run.
Direction and Length of Veins.
It has already been remarked that the regular or metalliferous veins generally take the direction of about East and West; there are others both in the same and in different directions, most of which are very rarely found to produce any metallic substance; the nature and peculiarities of these will be noticed hereafter. The regular veins are almost uniformly of considerable length; some are known to extend two or three miles, having several mines on their run; and though the idea of their extending the whole length of the county may be judged to be hypothetical, it ought to be noticed that the most experienced miner never satisfactorily witnessed the termination of a vein either on the East or West. Many circumstances of disaster, and more particularly that of poverty, occur to prevent their extent from being known; but that there are instances of their appearing not to exceed a few fathom: in length, is evinced by the ground plans of Herland and Drannack mines, accompanying this paper. In reality however the veins of those mines did not terminate as represented on that plan, but continued both East and West, to an unknown extent, in strings so very small, as to be only just perceptible, and therefore not worth the attention of the miner, whose experience induces him to believe that when a vein diverges in metalliferous strings, however small, they would, if pursued, be found ultimately to increase in size, or to converge again, or to diverge to other veins, which are generally found to be, as it were, increased in size and value thereby. The East and West veins are sometimes found diverging from the straight line, even when apparently unaccompanied by any circumstance that might be assumed as the cause, but they generally return and resume their customary direction. In Huel Fanny, I think, the vein suddenly took a course to the South-East, in a few fathoms it was found to alter its course again, nearer East; afterwards it ran about East, and then elbowing again, it resumed its usual direction, nearly if not quite in a straight line. But circumstances of this kind are by no means common.
Underlie of Veins.
With the exception of those alluvial depositions of tin, found in vallies and low grounds in many parts of the county, and in the working of which the tin is separated from its accompanying earthy substances by means of passing a stream of water over it, whence they have been called stream works, neither copper nor tin is found in Cornwall in layers or beds. The veins, in which only they are found, have a downward direction, not perfectly perpendicular to the horizon, but inclining more or less to the North or South; this inclination is called the underlie of the load, which in some veins does not exceed a few inches in a fathom from the perpendicular, but in others is a fathom in a fathom, or even more.
When two metalliferous veins underlie in opposite directions, that is, one North and the other South, and meet underground, the result is not always favourable to the miner; for even though they might have been rich when separate, they generally are found to be poor at and after their junction. But when two lodes underlie in the same direction, and one of them quicker than the other, it is generally found that when the latter overtakes the former, they seem mutually to enrich each other.
Veins are not very frequently found to separate in the downward direction, so as to make branches forming distinct veins, having an opposite underlie. Instances of this however occurred in Tin Croft Mine, of which a Section is given.
Depth of Veins.
Not an instance, I believe, has occurred of a vein having been cut out in depth. When the working of a mine is relinquished, it is mostly either on account of its poverty, or the expense of sinking to a greater depth, being to a larger amount than the product. The mine called Crenver and Oatfield is 200 fathoms deep; Cook's Kitchen is 210; and Dolcoath 228 fathoms; these are the deepest mines in the county now at work.
Width of Veins.
The East and West, or metalliferous veins, are generally from one to three feet in width, but vary to 30 feet. In the old workings of Relistian mine for tin, there are chasms, both open to day[3] and underground, full 30 feet wide. A vein from one to three feet in width is preferred, because, though many instances of the contrary have occurred, it is found that the product is generally as good as in wider veins, on account of there being, for the most part, less admixture of foreign substances with the ore.
A vein sometimes varies in width in the same mine very materially, and is often found to increase in that respect in going down. One of the lodes in Huel Alfred[4] varies from 9 to 24 feet: there is a peculiarity in its direction which is noticed in speaking of that description of irregular veins called Contres. As opposed however to the width of that vein, those of Herland and Drannack and Prince George mines, which are separated from Huel Alfred only by a brook and a cross vein, may be cited. There, instead of continuous veins of a somewhat irregular width, they are remarkably small, most of them varying only from 2 to 6 inches in the widest part, which was about the middle, and going away East and West in mere strings. A tin vein in Whealan Coates mine, not 3 inches wide, was very rich, and found to be worth working.
If in working on the course of a vein, or in sinking through the load, the country is found to assume a greater hardness in a very considerable degree, the vein generally becomes narrower.
Denominations of Metalliferous Veins.
The substances which form the contents of the metalliferous veins differ very materially; nor are veins distinguished simply by the name of the ore for which they are wrought, as a Copper Load, or a Tin Load; but they have obtained various appellations, according to the nature of the substances found to predominate in them. For as the greater proportion of the contents of most of them, is neither the ore of copper nor that of tin, the miner in speaking of them, gives them the appellation which is technically descriptive of the vein-stones:—as a gossany, sparry, mundicky, peachy, flucany, scovan, caply, pryany, black jack, and a grouany Load.
Gossan is a friable ferruginous substance, consisting generally of clay, or of some siliceous matter of a loose texture, coated or tinged with iron, in various proportions, arising probably from the decomposition of pyrites; it varies in colour, from pale yellow to deep red, sometimes inclining to black. A Gossany Lode is more common than any other, and most promising both for tin and copper. Gossan has been plentifully found at small depths in many mines that produced considerable quantities of one or the other metals, both beneath as well as mingled with it; as of tin in Huel Sparnon and Pednandrae, and of copper in Huel Gorland, and in East and West Huel Virgin.
When the load or contents of a vein is termed sparry, this does not imply that it is of solid spar or quartz, but that quartz predominates. A vein in which this substance is considerably compact is very unpromising; and if at the same time the vein becomes narrower as it descends, it is generally relinquished as a hopeless undertaking; which was the case in Huel Gorland, as noticed in my memoir on the red oxide of copper.[5] A vein abounding in fluate of lime is often termed a sparry load. Quartz is sometimes called hard spar by the Cornish miner, and fluate of lime, sugary spar.
If iron pyrites abound, the load is said to be mundicky, and when this occurs at a shallow level it is not always unpromising: even if it continue in depth, and be somewhat compact, particularly if mingled with portions of yellow copper ore, there are many instances of such veins proving rich beneath. No distinction is made by the miner between iron pyrites and arsenical pyrites. The latter is however rarely very abundant.
A vein that contains a great proportion of chlorite is termed a peachy load: it promises for tin rather than copper, which is rarely accompanied by chlorite. Tin was found in it, in Pednandrae, Polgooth, Relistian, Huel Unity, and in many other mines. I have specimens of the yellow copper ore in chlorite from Relistian and from the Wherry mine, the workings of which were under the sea in Mounts' Bay.
A vein is said to be flucany when either one or both its sides, or walls, are lined with a whitish or bluish clayey substance, or when this substance is interspersed through the vein itself. Flucan in some few instances has abounded so greatly, that it has been difficult to prevent its running in upon the miner in working the mine. This was the case in the early working of the productive copper mine called Huel Alfred, as is noticed in the annexed description of some of its veins.
When tin ore is intimately mingled with quartz and chlorite, the vein is termed a scovan load, which is of a dark brown or of a greenish hue, but not very hard, or compact. A load of this description rarely exceeds 12 or 14 inches in width, but it sometimes occurs in a vein the contents of which are not solid, thence by the miners termed a sucked stone. A load so circumstanced is often several feet wide.A vein is termed a caply load when consisting of a hard, compact and unpromising substance, which seems principally to be quartz intermix with minute portions of chlorite, giving a greenish, or brownish green tinge to the mass. Tin is often found in it, copper rarely. But if a branch of copper ore, or a gossan be found to take its course down the vein, it commonly makes a durable copper mine.
A vein is said to be a pryany load, when the tin or copper ore does not occur in a compact state, but when the stones containing either of them are found mixed loosely with other substances, such as gossan or flucan. Pry in the Cornish language signifies clay.
A vein that abounds in blende is called a black jack load, which is generally unpromising for tin, but is considered a good omen for copper. It is rarely found that blende continues to any considerable depth. It is also called mock-lead by miners.
Grouan[6] is the common technical term for granite, so that when a vein abounds in that substance, either in masses or blocks, or in a decomposed state, it is called a grouany load, which is rarely found except in a granite country. Grouan is more promising for tin than for copper; though veins containing the latter have often of late been found in the granitic districts of Cornwall, of which the western part of West Huel Virgin, Carharack, and Huel Damsel, all rich copper mines, are instances.
It must be remarked that veins generally take their names from the substances which abound but a little way below the surface. But, the circumstances of veins change so often, and their contents frequently participate so largely of the nature of the country they traverse, that the same appellation will not often hold for them in depth. A satisfactory trial of their nature and value can rarely be made, without sinking 30, 40, or even 60 fathoms below the surface, and driving, at various depths, east and west on the “course of the load.”
Symptoms in Veins.
In the whole range of the employments of man, there is not perhaps another in which experience and ingenuity are more often and completely baffled than in mining. Not unfrequently the appearances in a vein considered to be of the most promising kind, lead on the most experienced miners during the lapse of many years only to ultimate and immense loss; while on the other hand, from the product of veins, which by men of not less experience have been declared to promise no advantage, large profits have been reaped. The great copper mine called North Downs, in the working of which no less a sum than £90,000 was lost, may be considered as an instance of the first, and Huel Alfred, from which a greater sum has been gained, is an instance of the second. There is scarcely one symptom on which the miner most relies that has not occasionally deceived him. It may be curious however to add some of the symptoms in favour of which the miner is greatly prejudiced. There is no one more favorable in his estimation than a gossany load. I remember that of North Towan Mine was of this description, and of so great promise, that several of the most experienced practical miners did not hesitate to declare it superior, in that respect, to any other they had seen; and that, if compelled to venture all they possessed, in the working of any one vein, it should be that of North Towan; but, after much time and expense had been bestowed in trying it, it was found to be very poor, and was therefore abandoned.
The early discovery of iron pyrites and portions of yellow copper ore mingled with a large quantity of blende is considered a favorable omen for copper. Blende, as has already been noted, is by the miner called Black Jack; and ‘Black Jack,’ he says, ‘rides a proud horse,’ a phrase become proverbial, from blende being often found to lie above, in a vein rich in copper beneath. Vast quantities of it were found above the ore in the productive copper mine Huel Towan, as well as in that called North Bennar. The early discovery of lead is also considered a good symptom; very many tons of it were sold from Huel Alfred in the states of sulphuret and carbonate. Iron pyrites at a small depth is, also considered a favorable symptom for copper in depth, as was proved among many others in the rich mines of Crenver and Huel Virgin; but when it proves solid, it has often discouraged the miner and induced him to abandon the vein. The cutting of a ‘good course of water’ is esteemed no unfavorable circumstance, especially if it be warm, and it is not uncommon to find water issuing from one part of a vein of a temperature sensibly higher than that in other parts of it. So greatly indeed does water abound in rich veins, that on extensive and deep mines are mostly seen two, three, and even four steam engines, for the purpose of drawing it, the cylinders of which are from 30 to 66 inches in diameter. If a vein be particularly rich, it is considered to omen well for the parts of other veins immediately north and south of its riches; to express which the phrase of “ore against ore” has been adopted.
It would scarcely be correct to say that the early discovery of tin in a vein is a good promise for copper in depth, but it is certainly true that tin is frequently, if not mostly, found at a small depth in veins, afterwards proving rich in copper. Among many other instances of this that might be quoted, are the two deep and extensive copper mines called Huel Unity and Cook's Kitchen, both of which were, I believe, worked for tin at first, without any suspicion of their veins being rich in copper beneath it. In both the tin was soon exhausted; but it should be noticed as an uncommon circumstance, that in the latter mine, after working to the depth of 180 fathoms, first through tin and afterwards through copper, tin was found again, and has continued down to the present depth of the mine, which is about 210 fathoms from the surface. It ought however to be noticed that some parts of that portion of the load which principally contained copper ore, had been left, on the presumption of their not yielding ore of any sort; in the phrase of the miner they were considered as deads. Some of these have since been found to produce tin, which may consequently be said to have prevailed more or less from the surface to the bottom of the present working. A considerable proportion, if not the chief part of the copper ore of this mine, was the sulphuret.
Among the favorable symptoms to which the miner is attached there is still another, which ought not to be forgotten. There are some among them credulous enough to believe that they hear, while employed under ground, another pick at work, which is immediately referred to the agency of an invisible spirit, or what they term a piskey, or small man. This is esteemed an omen of the most favorable kind, and which induces the full belief of having nearly arrived at the desired object, the discovery of ‘a good course of ore.’ It seems as though the sound which the miner hears, may reasonably be accounted for by presuming him to be at work in the immediate neighbourhood of a cavity, or as he terms it, a voog, which returns the sound of the stroke of his own pick. Discovery of Veins.
The discovery of metalliferous veins is effected in various ways. Amongst the foremost of these, Pryce places that of the Virgula Divinatoria; but, after a long account of the mode of cutting, tying and using the rod, interspersed with observations on the great difference existing in the discriminating faculties of constitutions and persons in its use, altogether rejects it, because ‘Cornwall is so plentifully stored with tin and copper lodes, that some accident every week discovers to us a fresh vein,’ and because ‘a grain of metal attracts the rod as strongly as a pound,’ for which reason ‘it has been found to dip equally to a poor as to a rich lode.’ Them it must be acknowledged, are substantial reasons for the neglect and disuse into which the rod has fallen. There are not however wanting even now, in Cornwall, some who maintain the value of it. I am acquainted with one person who has repeatedly declared to me that, while using it in his own shop in the town of Redruth, he discovered a vein which has since formed a part of the workings of Pednandrae mine for tin. On the other hand, an intimate friend well conversant with mining concerns was present in Somersetshire with some nobleman and gentlemen, the proprietors of land in that county, anxious for the discovery and working of veins supposed to run through their estates, when a person who professed the skilful use of the divining rod assured them he could effect their wish. During one of his attempts, my friend, as though by accident, took his station immediately facing the professor of the rod, who advanced with the rod dipping as he declared to the run of a vein; my friend retreated, and in his retreat made a circuit, which as he had in some degree caught the attention of the person holding the rod, was followed by him; and the pegs that were inserted in the places his feet had touched proved the circuit he had made. If a vein actually ran in that direction, it is certainly wholly different from that of any known vein. It is almost needless to add, that the discovery of the supposed veins as indicated by the means of the divining rod, was not attempted.
The ancient mode of shoding for tin-veins, consisted in tracing certain stones, of which tin formed a proportion considerable enough to excite attention, and found at or a little below the surface, to the vein from which they had been accidentally detached, so as to have passed in a sort of succession down the side of a hill. Another mode of seeking tin veins is by sinking pits through the superincumbent earth down to the solid rock, and driving a trench from one to another, north and south, so as to meet with every vein in the track through which it passed. This method, which is also esteemed to be very old, is called costeening.
The former of these methods for the discovery of tin veins is now rarely resorted to; but the second, as well as another which differs not much from it, that of working drifts across the country from north to south, is sometimes practised. Many tracts of the mining part of Cornwall are however so amply stored with veins in the direction of East and West, that there is little occasion to employ either of the above mentioned modes of discovery. There are comparatively but few mines which are known to have within their boundary only a single vein; in some there are 5, 6, or even 7. As the driving of an adit home to a vein is one of the first and most important tasks of the miner, he sometimes embraces the opportunity of so doing from a neighbouring valley along a cross course, or North and South vein, and for two reasons; the first, that the expense is less than if he were to drive through the solid country the second, that he has at least a good chance of meeting with all the veins between the extremity of the adit and the vein to which he intends to drive it. Yet of this he is not altogether certain, for the east and west vein is sometimes so greatly disordered by the cross vein, as that it might wholly escape the notice of the miner; besides, cross veins often divide into branches, so that the miner runs the hazard of following the wrong branch, and thereby of missing altogether the metalliferous vein. But although the mode of discovering veins, by driving an adit along the run of a cross course is at once the cheapest and most expeditious method, it is not always practised, as the foresight of the experienced miner sometimes induces him rather to drive through the solid country than to hazard the chance of being obliged to draw the water of the country all around him, which he is aware the cross vein would prevent from troubling him on one side.
Accident often occasions the discovery of veins. That of the mine called Huel Maggot, or Velenoweth in the parish of Phillack, was first seen by workmen employed in digging a trench for the foundation of a garden wall in a valley. It there consisted of a rich gossan, which in the phrase of the miner was very kindly. On driving into the hill, a few fathoms on the ‘course of the load,’ it produced abundance of sulphat of lead in well defined crystals, sometimes accompanied by the sulphuret, and sometimes deposited on the gossan, and, a little deeper, copper ore in considerable quantity. Both were however soon exhausted, and the mine was abandoned. The run or course of an east and west vein may sometimes be traced on the surface, by loose fragments or portions of earthy or stony substances, having generally more or less of an ochreous tinge, but this, which is called the ‘bryle of the load,’ has rarely a regular separation from the country on each side of it. But in sinking a few fathoms below the surface, it assumes more determinate marks of being a fissure.
Contents of East and West or Metalliferous Veins.
The contents or load of the generality of veins, if at all attached to their sides, are for the most part easily separated. A dark ochreous crust occasionally covers one or both sides of the vein, technically called the walls of the load; and when these, or at least one of them, is regular and determinable, they are more encouraging to the miner than when rough and uneven. A thin coating of flucan is found on one, or occasionally on the other wall, or sometimes on both walls of a metalliferous vein, as described by pl. 6. fig. 4. but it is said that this coating or vein of flucan is most commonly found on that which, in regard to the underlie of the vein, may be called the upper wall.
It has been already noticed, in speaking of the denominations of metalliferous veins, that there is a great diversity in their loads or contents, and that the same vein exhibits so little uniformity in that respect, at different depths, as to assume various characters. Near the surface the load consists for the most part of a sort of ochreous rubble, probably the debris of the neighbouring country; beneath which, though rarely nearer grass than 20 or 30 fathoms, are found some metalliferous indications. These, if gossan be the prevailing substance, consist of the ores of tin or copper. But iron pyrites, blende, fluate of lime, quartz, and sometimes chlorite, or flucan, frequently prevail for many fathoms, occasionally mixed with portions of the country through which the vein passes, though frequently with but slight traces either of tin or copper. A vein is sometimes found to consist of little else than a bed of hard and unpromising iron pyrites, which occasions its being abandoned; in others are found the ores of tin or copper, sometimes both, intermingled with some, or even most of the foregoing substances; but if they occur together, the copper for the most part prevails to such an amount, as that all traces of tin are lost in depth. In some veins however they continue to be found, even to a considerable depth, though not often much intermingled but in separate bunches; this as has already been noted, was the case in Cook's Kitchen Mine; the neighbouring mine, Tin Croft, also furnished a somewhat similar instance, though not I believe in the same vein; but these must be considered as somewhat rare occurrences.
Tin is commonly found much nearer the surface than copper. When either is very near, especially if abundance, it is in the estimation of the miner an indication that it will not continue to a very considerable depth, of which Cornwall furnishes numerous instances. There is a tract of country situate about midway between Truro and Redruth on the north of the high road, in most of the mines of which, and amongst them the great mine called North Downs, the ore for the most part occurred near the surface, and was almost uniformly found to extend but to a small comparative depth.
Although there are veins in various parts of the country which have yielded copper in its pure state in considerable abundance, in masses interspersed through them, and but little intermingled with other substances, or even with the ores of copper, yet the most common state in which this metal is found is that called yellow copper ore. It is more continuous and lasting than any other. There are veins which yield only the grey sulphuret, but this rarely or never continues, being found only in bunches. It is sometimes mingled with the yellow ore. As a proof of the great difference in the value of the ores of veins, it may be noticed that there are many which seldom yield it of a greater price than £4 or £5 per ton. A few tons were lately sold from the United Mines at £100. The general average perhaps does not exceed about £7. 10s. or £8 per ton.
In few metalliferous veins does the ore prove so continuous, as after it has been taken away to leave a large hollow load. The intermediate spaces between the ore are mostly filled with what the miner terms deads, which consist of quartz, fluor, gossan, iron pyrites and other substances, as well as occasionally portions of the country through which the vein runs; but the walls of the vein are nevertheless generally determinable. The deads are not always a disadvantage to the miner, as they serve to keep apart the country on either side the vein; but for this purpose, when the vein has been left hollow by taking away a large body of ore, strong timbers are made use of; these are not however always found to be of strength sufficient to prevent the falling in of the cavity. An instance of this occurred in the copper mine called Huel Alfred; one of the veins of which was hollowed out for about 100 fathoms in depth, 80 fathoms in length at bottom, and 80 fathoms above, and varying in width from 9 to 24 feet. Notwithstanding great labour, skill and expense had been bestowed, and the most substantial timber employed in order to keep apart the walls of the vein, many thousands of tons came down in an instant; fortunately seventeen men who had been working in the very place on which the whole fell, had left it half an hour before the accident. The whole has been supported, and they are now working beneath it.
It has sometimes happened that in a large load, and where it is largest, the miner has suddenly arrived at a piece of dead ground in the middle of it, which in depth spreads wider so as to occupy nearly the whole of the vein, leaving on each side only a small connecting string of ore. This has been known to extend many fathoms in length and depth, and from its being narrow above and widening below, it has obtained from the miner the name of a horse. The phrase on meeting with it is, ‘the load has taken horse.’
The riches of a mine have in many instances proved the cause of great speculation, and consequent disappointment to those concerned in the mines immediately contiguous east and west, and on the same vein or veins. This has been but too unfortunately verified in the instance of East Towan Mine, which joins Huel Towan on the east; in the latter, which has during the last 10 or 12 years, from one large and unusually continuous bunch of yellow copper ore (the discovery of which was the result of a search of at least 30 years at a greater expense) yielded a very large profit. There were 50 fathoms of good ore-ground in the vein at about 66 fathoms under the adit, which adit is 42 fathoms from the surface, or in the technical language of the miner, from grass. The bunch of copper ore continued to that depth from near the adit level, and as in length it extended east towards East Towan Mine, expectations were raised that the load in passing through that mine would prove equally rich. Great speculation and expense of course ensued; but in vain. For it was found that in several of the levels in Huel Towan, the ore ceased within a very few fathoms of East Towan Mine, and in some places as suddenly as if it had been cut away by a hatchet. This was not the effect of a cross vein, but purely one of those accidental circumstances to which copper loads are very liable. The ore of Huel Towan is of a remarkably bright yellow, and generally pretty compact, but not hard.Adits.
When it has been determined to try a vein, one of the first objects of the miner is to bring home an adit to it. An adit is a water course, or rather an underground passage, about 6 feet high and 212 wide, and is begun at the bottom of a neighbouring valley and driven up to the vein, for the purpose of draining it of water above their point of contact. In the event also of the mine having a steam engine upon it to raise the water from a still greater depth, it is not raised by the engine to the surface, but delivered into the adit. The general level of the mining-country East and west of Redruth is, according to Dr. Berger, from 350 to 450 feet above that of the sea, except where the granite overtops the schist, as in the instances of Cam-brae, Carn-math, and some few other hills, the summits of which are at a considerably greater elevation. This general level of the country is intersected by frequent vallies, which afford great advantages for the formation of adits, and consequently for the carrying away of the water from the mines. One adit frequently serves this purpose, for 2, 3 or more mines. Pryce, who published his work, entitled Mineralogia Cornubiensis, about 30 years ago, says p. 148, ‘Though we seldom see an adit half a mile in length, there are 2 or 3 of three times that length, these are the longest I know of.’ But since his time, one has been driven through a considerable tract of country at the lowest possible depth, as its mouth or extremity is nearly on a level with the water in one of the creeks of Falmouth harbour, into which it empties; and being below all other adits in that neighbourhood, it is called the deep adit. It does not run in one course, either direct or circuitous, the whole of its way; but taking into calculation its various branchings in and through the numerous mines (those of Gwennap) which it relieves of their water, it may be said to be about 24 miles in length.
Taking into consideration the purpose of an adit, it might be presumed that it is wrought on an inclined plane from the place at which it joins the vein to the extremity in the valley. This may perhaps be the case with some, but the practice is not uniform. By making them on an inclined plane, a freer current would be given to the water, yet much of their benefit would be lost, even although their declination were not to exceed one inch in a fathom. For, in supposing this plan to have been pursued in the driving of the deep adit above mentioned, which, from its extremity to North Downs mine, is about four miles or 3520 fathoms long, it will be obvious that if a declination of one inch in a fathom be allowed, the elevation of the adit at North Downs mine would be about 300 feet above its extremity; an elevation nearly if not quite equal to that of the surface of the mine. If therefore in the driving of an adit any allowance be made for the current of water it may be presumed that the interest of the miner will induce him to make it as small as possible.Country.
Veins containing copper, as well as those containing tin are found both in granite and in schist, though until within the last 50 years, it was esteemed in Cornwall a hopeless expectation to find a vein containing copper in the former of these rocks. Experience has however in many instances, in the parishes of Redruth and Gwennap, as well as in some others, proved that veins of copper ore are found in granite. In both of those parishes granite and schist have in some mines been found to alternate; this alternation has not, as I conceive arisen from their stratification, but from the casual unevenness of the first being supplied by a deposition of the second. It has, I believe, been but rarely noticed that the course of a vein has been along their junction; but some instances of this have certainly occurred; and I was informed by Capt. William Davey, of Redruth, one of the most skilful and intelligent practical miners of the present day, and who was the principal manager of Huel Gotland mine, that for some fathoms both in length and depth one wall of one of its veins was of granite and the other of schist; another instance is mentioned in the annexed notice of the accompanying section of Tin Croft mine.
The alterations in the country from schist to granite and back again to schist, are very frequent in some of the mining districts of Cornwall, so that it is impossible in a word to say in which some of the mines are situated, but I suspect this to be principally the case with those mines that are at the foot, or in the immediate neighbourhood of granite hills. I have not noticed any instances of the junction of these two substances in which the granite has not shewn a tendency to decomposition: it is sometimes separated from the schist by a slight ferruginous seam.
It will of course be understood that great variations in the texture and hardness both of granite and schist are observable. Of the former there seems every possible difference in hardness between the decomposed granite of Tol Cam mine, which, as well as that of several others, it was impossible to keep apart without lining the adit or the level with boards close to each other, both above and on each side, and the compact and fine grained granite, of which quartz forms a principal ingredient, and which in hardness is almost equal to porphyry. Of the great difference in the hardness of schist, I shall notice one instance in Huel Allred; in the sinking of two shafts in that mine, not much exceeding the distance of 50 fathoms from each other, the pay to the miner was in one instance £55 per fathom, but in the other only at £5.
These frequent variations in the country through which the miner is under the necessity of passing in the usual course of his occupation in the sinking of shafts and driving of levels and adits, often prove the occasions of great hindrance and loss. There is a narrow channel of a remarkably fine grained substance consisting of compact felspar and chlorite, running in the direction of east and west, a little north-west of Redruth, which is so exceedingly hard as to have obtained the technical name of Ire-stone or Iron-stone. It was met with in driving an adit towards a mine, the Old Pool, I believe, and it has often been told me, that it was so remarkably compact in one place as immediately to turn the point or edge of every tool, so that it was found impossible to drive a hole deep enough to employ the blast by gun-powder: the miner was compelled little by little to pick through that part of it, in doing which the seat-board was not once moved forward during the space of 12 months.
The schist of Cornwall varies much in colour as well as in hardness. It passes from lightish grey through the shades of slate colour to that inclining to a reddish hue, which is considered to be promising as to the occurrence of tin. But that which is esteemed the most kindly both for copper and tin, as well as the least expensive in the working, is of a light grey colour inclining to slate. This kind of schist is easily broken, and may be left without much support, and is therefore what the miner terms feasible ground, but it often passes in depth into a far more compact kind, of a dark colour, inclining to blue.
Cross or North and South Veins.
It has already been noticed that there are veins in Cornwall, which as they are found almost uniformly to traverse the east and west or metalliferous veins[7] in the direction nearly of north and south, are technically termed Cross Courses. They rarely produce copper or tin, or any other metallic substance. They vary from half an inch to a few feet in width: the underlie of some is east, of others west; others again have little or no perceptible underlie, but are nearly perpendicular to the horizon. In some tracts of the mining country they are of very frequent occurrence, as the accompanying ground plan of Herland mine will evince.
Cross Courses, or north and south veins, may be subdivided into 1st. a Quartzose vein, to which the general term of Cross Course has been given—2nd. a vein containing a soft marly or clayey substance of a bluish or whitish appearance, called a Flucan; and 3d, a vein containing a substance of an ochreous and friable nature and of a yellow colour, called by the miner a Cross Gossan. Every cross course or cross gossan is however accompanied by a flucan. In speaking of these veins the miner sometimes gives them their technical appellations, but he is more habitually disposed, whatever the substances of these veins may be, to call them by the familiar term of cross courses.
The principal advantage derived from the north and south veins is that, when their substance is flucan, or even when a continuous vein of flucan, however thin, accompanies the quartz or gossan, they prevent the water of the neighbouring country from troubling a mine, and they are sometimes left to perform that useful office, as was the case between Huel Sparnon and East Huel Sparnon, near Redruth. But their disadvantages are numerous; for although the regular metalliferous veins are occasionally found to be but little or not at all disturbed by the passing of the substance of the cross vein through them, except by the mere division of the load, it more often happens that it is as it were broken into small strings or branches. By a careful examination of the nature and direction of these, the miner is indeed sometimes enabled to find pretty readily that part of the load which is on the other side of the cross vein, but he is often baffled. Instances have occurred in which the load has, as it were, been turned. by the cross vein, so as to form what the miners term an elbow.
Not only does the substance, whatever it may be, of the cross vein, almost uniformly pass through that of the metalliferous vein, but it is often found so to interrupt its course, as, in the phrase of the miner, to heave that part of the vein, east or west of it, a few inches, or even many fathoms north or south: and as the metalliferous vein is frequently found to be poor on one side of the cross vein, though rich on the other, its occurrence sometimes not only baffles the skill of the most experienced miners, but also causes much loss and vexation, as the annexed account of some peculiarities in the veins of Tol Carn, Huel Jewel, and Huel Damsel mines, will shew.
Though the cross courses, or north and south veins, are rarely found to be metalliferous, or even to yield any of the ore of the east and west veins through which they pass, a general exception was found to exist in those of the great tin mine near St. Austle, called Polgooth, in which, I believe, they universally produced tin. Two of the cross veins in Herland and Drannack mines yielded silver—one of them very sparingly, in the other it was accompanied by other metallic substances: the quantity of silver amounted in value to 8 or £9000. Pryce says[8] that cobalt has been found in veins of this description, that others have been worked for lead, and [9] that the direction of antimonial veins is mostly north and south, but that he had not known ‘any producing that mineral of more than fourteen fathoms deep.’ The mine called Huel Boys, which formerly produced the triple sulphuret, is now worked for antimony, which occurs in bunches of various dimensions in a vein, the direction of which is nearly north and south, and of about five feet in width. The antimony is accompanied by blende only, and is not now found in a state of crystallization. The country through which the vein runs is schist.
Slide.
Veins, not of a metalliferous kind, but which contain gossan, or flucan, are sometimes found running north and south, with an east or west underlie, generally very quick, one of which will be noticed on a reference to the section of the Manor Old Vein. Veins of this description are also found in the direction of the metalliferous or east and west veins, having an underlie north or south. But whether their direction be east and west, or north and south, and whatever their underlie, they are frequently the cause of much expense and vexation to the miner. When the underlie of this species of vein is in the same direction as that of the metalliferous vein, but quicker, so as to overtake it in depth, the latter is generally divided by the former, and, as it were, removed from its regular course. The load of the metalliferous vein is also sometimes altered in respect to its value, above or below its section, and the space between a and b, Pl. 6. fig. 2. as it regards the load, is as it were lost. This kind of vein, from its direction, has obtained the name of Slide, and the phrase is, ‘the load is cut out by a slide;’ its flucan or gossan, generally traverses that of the north and south, as well as the east and west veins.
Heave.
But when the underlie of this species of vein is in opposition to that of the metalliferous vein, the effect of it is immediately the reverse of that of the Slide, and is called the Heave. Pryce has noticed a remarkable instance of this which occurred in the Goon Laz and Pink tin mines, in the parish of St. Agness. The tin load underlaid north, the gossan vein south. (Pl. 7. fig. 7.) At 62 fathoms in depth, it separated the tin load at a, heaving the other part of it up to b, 22 fathoms in perpendicular height, and 19 fathoms horizontally north. Another gossan vein afterwards cut the tin load at c, heaving it up to d. The tin load then resumed its course, until another gossan vein separated it at e, heaving it up to f.
It will be observed that the effect of the heave is than of affording a greater portion of the tin load at a given depth from the surface, than would have been the case had the vein pursued its regular downward direction. But this is not always a compensation to the miner; for the vexation and expense accruing to him in searching for the tin vein generally exceed any advantage to be gained by the heave. It was, I believe, principally the effect of a heave that baffled the skill and experience of the most eminent practical miners in Huel Peever; in which mine they were, during about 40 years, in search of the load, and which was at length discovered. Perhaps the history of that mine, and of the long and vexatious search, occasioned by the loss of the vein, would prove the most satisfactory evidence that can be obtained of the strange phenomena occasioned by the heave; and I have the satisfaction of knowing that it is the intention of a gentleman, who has nearly completed an account of it, to present it to the Geological Society.
In describing that effect produced by the interruption of one vein by another, called the heave, it ought to be noticed that a copper vein going down with a quicker underlie than a tin vein, always passes through it, and sometimes interrupts its regular course. And if the underlie of the copper vein be south, and that of the tin vein north, or vice versa, the copper vein continues its course, but interrupts that of the tin vein, heaving it out of its first direction; and although Pryce has merely given the appellation of ‘Gossan’ to those veins that heaved the tin veins, as just noticed, it seems to me probable that these ‘Gossans’ were veins containing copper, which is rendered the more so, as the term ‘Gossan’ is frequently given to a copper vein, merely from its being the prevailing substance. The heave of a tin by a copper vein was, I believe, one of the remarkable and complicated disasters which befel the veins in Huel Peever.
Feeder.
A small metalliferous vein or string is sometimes found to take the same course as the east and west vein, (Pl. 6. fig. 3.) When its underlie is so much quicker than that of the latter, as to overtake it in going down, the metalliferous vein is generally found to increase in size, not merely in the proportion of the addition of the lesser vein, but very much more, so as to make a great body of ore, called by the miner a gulph of ore at their junction. This species of vein is therefore termed a Feeder.
Leader.
While working in the course of a load, small metalliferous branches or strings are occasionally observed to strike into the vein from the north or south, which, it seems probable, have before diverged from the same, or some neighbouring vein, (Pl. 6. fig. 5.) It is not certain that copper veins are equally subject to this circumstance as are those of tin. In Polgooth and Carnmeal tin mines, their effect was the sudden enlargement of the load to what is termed a floor of tin, twelve feet or more in breadth, but without the determinate walls usually observable in regular veins. A floor of tin rarely continues for any considerable length or depth, and the load is generally soon found to resume its usual size and appearance. From the common effect of this kind of branch or string, it is generally known by the term leader.
The Contre.
There occurs still another species of vein, of which the course or direction is generally about north-east and south-west, and which therefore is oblique in respect to all other veins; from this circumstance I presume it to have obtained the name of Contre or Counter. They are mostly, if not always, metalliferous; several instances have occurred of their being remarkably rich. Two instances will be noticed in the annexed descriptions of Huel Alfred and Herland mines, in both of which they were very productive of copper ore.
It may here be noticed, that in the former of those mines, the regular or east and west vein was disturbed by the contre, and for some distance totally disappeared on the west. In the latter, both the load of the regular vein and that of the contre were enlarged, and became more productive by uniting.
Elvan.
Elvan is one of the three grand distinctions made in regard to rocks by the Cornish miner. Whatever is not grouan (granite) or kill as (schist), is of course with him elvan. So that, in fact, it is extremely difficult to say what it is or even what it is not, with the exception of granite and schist. The substance to which it is most commonly applied occurs frequently in Cornwall, not as forming tracts of country, but interposed between the schist, in what is termed by the miner a channel. I know of no instance of its thus occurring in granite. The situation of these channels is not horizontal: they generally dip at various angles with the horizon, and in various directions. The colour of elvan is bluish-grey, or yellowish. It does not always disturb the contents of the metalliferous vein, which generally continues through it, though the load is mostly narrower than when in the schist; but it sometimes has the effect of dividing it into small branches. By the accompanying section, of Pleasure, Fancy, and North Herland veins, Pl. 8. fig. 10. it will be seen that a large channel of elvan took a course opposed, though not opposite, to that of the metalliferous vein, and that two other channels took similar directions by the section of the Manor Old Vein, fig. 11. The examination of some specimens induced me to consider the elvan of these mines to consist of crystals of quartz and felspar imbedded in compact felspar; in one specimen, the latter was intermixed with compact quartz.
In the preceding pages I have aimed at giving a mere general outline of facts, which, considering the imperfect state of geology, seems to be rendering better service to science than could be derived from a feeble attempt to raise upon their basis any theory explanatory of their occurrence. Nor indeed is the knowledge of insulated facts sufficient to authorize such an attempt on this important and difficult subject, comprehending operations on so grand a scale, of a date so remote, and throughout a country so greatly diversified. Before such an explanation can be satisfactorily accomplished, we have much to explore and to learn. The task seems to require a combination of talent and of information, which but rarely exists. But that a faithful detail of mining facts may contribute to assist the geologist in his inquiries, can no more be doubted, than that the science of mineralogy is absolutely essential to assist him in his researches.
It is to be regretted that the practical miner, in every part of England, is almost wholly ignorant of the principles and facts of mineralogy and geology. Even the conductors of the mines, termed captains, are men generally of little or no education, who have risen to that station by a superior attention to their art, in which they have been incessantly occupied from the early age of five or six years. A century ago among the miners of Cornwall, whatever was not tin was heedlessly thrown aside; and within that period, on the discovery of copper ore beneath the tin, it was no uncommon observation, that the ‘ore came in and spoilt it.’ It is an undoubted fact that many roads in the county were mended with copper ore. The discovery of the native silver in Herland mine would have passed unnoticed, but for the vibrations of some capillary portions having accidentally attracted the notice of a workman; and it is confidently believed that much of that precious metal has been thrown away on the neglected heaps of that mine. Even now, whatever is not manifestly tin or copper, or is not suspected of yielding those metals, is paid little attention to; and the practical miner sees no value in the inquiry into the run of veins, the nature of the country they traverse, their contents, or uniformity, further than relates in his own estimation to the immediate benefit of his occupation; and he smiles at the nice discriminations of the mineralogist. If an inquiry into the phenomena of veins be made of him, he refers, by one short cut, to the universal deluge.
The total ignorance of almost every thing relating to the sciences of geology and mineralogy, and above all of chemistry, in the conductors of mines, and their agents, is not only matter of regret, but it can scarcely be doubted, is also the cause of much loss to the adventurers in mines, to the lords of the soil, and to the buyers of the ore. If a spirit of inquiry had existed, which some knowledge of these sciences could not have failed to produce, much cobalt would not have been thrown away on the heaps of Dolcoath and some other mines, nor would bismuth in Huel Sparnon have been mistaken for cobalt, nor would the roads have been mended with copper ore, nor would the ponderous ore, which contained silver in Herland mine, have been left to the chance that discovered its value, nor would many miners, in opposition to all the known principles and properties of mineral bodies believe, even to this day, in the regeneration of metals.[10] While in France, and in Germany, there are national institutions for the education of those intended to conduct the working of mines, in the three important branches of science before alluded to, and which are so intimately connected with their occupation, in this country all is left to accident, and the rich gifts which nature has bestowed upon us, are consequently often neglected, or lavishly thrown away.
The ores of copper, as sold at the mine, though some of them are richer, do not in most instances contain more than one-twelfth of copper, frequently not one-fifteenth, some of them not one twentieth. The accompanying substances are a heterogeneous mixture of earths and metals, amongst which arseniates of various kinds often bear a considerable proportion. It needs not to be insisted upon that much attention ought to be given to free copper from arsenic, which is so very liable to render it brittle. When a pound or two of the ore is given to the sample-trier, as a fair sample of 50 or 100 tons, his report is but too often grounded on the weight of the prill he has obtained from a given quantity of the ore, without reference to the substances with which it may be alloyed, which indeed his skill does not enable him to detect. When the ore is taken from the mine, it is for the most part deposited, not that of each mine separately, but mixed with that of many others, without regard to the great difference that must of course exist in the ore of veins, circumstanced so variously as are those of Cornwall.[11] And strange as it may seem, it is notwithstanding true, that even the interest of the buyer seldom tempts him to swerve from the hacknied practice of his predecessors, in making purchases to an enormous amount on the reports of those whose skill only extends to the extracting of the heaviest prill, without possessing a knowledge of chemistry sufficient to enable them to discover of what it is compounded.
Enough has been said in the preceding pages of the uncertainties attending the pursuit of the miner, to amount to evidence that skill and ingenuity are often exerted in vain:—all they can do is to determine on, and put in practice the speediest and most effectual methods of ascertaining the value of a vein, at the least expense. When assisted by the best experience, they are utterly unable to form a conjecture, grounded on reasonable certainty, that the great expenses attending the trial of a vein will be repaid. If indeed the reverse of this were the case, there would not be as there now are, so many skilful captains of mines who have lost money by their adventures. If experience avails so little, theory cannot be expected to avail any thing; and it may fairly be doubted whether all that science could bestow on the practical miner, would, in this branch of his occupation, be found to be of the slightest advantage.
The habits of the miner are those of industry and perseverance, which often tempt him to exploits that excite astonishment at his venturous hardihood. The very idea of a descent beneath the surface of the earth has something in it of the terrible, at which those shudder who are unacquainted with practical mining. But such is the force of habit, that rarely does any other employment tempt a miner to forsake his own. The occasional perils of his occupation are scarcely noticed, or if noticed are soon forgotten. He walks often in the middle of the night, and in all weathers, two or three or more miles to the mine, undresses, and puts on his underground clothes, and with his tools slung over his shoulder, descends by ladders a depth of 1000 or 1200 feet, assisted by the light of a small candle, and works in the bottom of the mine six or eight hours, amidst the noise of the working of the pumps in drawing the water, with as much alacrity, and with as little sense of danger, as he would feel amidst his ordinary occupations above ground. We should be inclined to feel pity for the wretch who, as an atonement for his crimes, should be compelled to undergo what the Cornish miner voluntarily undertakes for a small pittance, and that even of an uncertain amount. ‘The mine of Huel Cock, in the parish of St. Just, is wrought eighty fathoms in length under the sea, below low water mark; and the sea in some places is but three fathoms over the back of the workings, insomuch that the tinners underneath hear the break, flux, ebb, and reflux of every wave, which, upon the beach overhead, may be said to have had the run of the Atlantic ocean for many hundred leagues; and consequently are amazingly powerful and boisterous. They also hear the rumbling noise of every nodule and fragment of rock, which are continually rolling upon the submarine stratum; which altogether make a kind of thundering roar that would surprise and fearfully engage the attention of the curious stranger. Add to this, that several parts of the load which were richer than others, have been very indiscreetly hulked and worked within four feet of the sea; whereby in violent stormy weather the noise overhead has been so tremendous that the workmen have many times deserted their labour, under the greatest fear lest the sea might break in upon them.’
The account of Huel Cock above cited, is extracted from the Mineralogia Cornubiensis of Pryce, page 21. I have made some use of the mining information contained in that work, which, though it is often confused, and sometimes scarcely intelligible, is, apart from its reasonings and its philosophy, a valuable production. I have not thought it necessary to acknowledge my obligations to it in every particular instance; nor, on the other hand, have I been willing to quote its authority, without verifying it by an appeal to some of my numerous friends among practical miners.
As an appendix, it seemed to me that some account of the veins of certain mines, remarkable either for their peculiarities or some striking geological fact, might therefore be an acceptable addition to the geologist, as well as in corroboration of what has preceded. I have however to express my regret that these relations are imperfect, inasmuch as little is said on the subject of the countries in which these mines lie. For as the information on that head could only be obtained from the practical miner; and as he notices the country merely as respects the ease or difficulty with which his operations are carried forward, or at most no further than regards his three grand distinctions of grouan, killas, and elvan, little or nothing satisfactory could be obtained, on that important part of their history.
Ground Plan of Herland and Drannack and Prince George Copper Mines.
Herland and Drannack mines are situated in a hill that rises suddenly on the west for some distance, but which is afterwards nearly on a level for about half a mile, the highest ground being about the center of that vein termed the Manor Old Load, having a gradual fall to the south of the middle mine. The country is schist, but in some places so hard as to require the blast by gun-powder. The general direction of the metalliferous veins is a little from the north of the east to the south of the west, and of the north and south veins or Cross Courses, a little from the west of the north to the east of the south.
Herland and Drannack and Prince George mines, and that called Huel Alfred, a description of some peculiarities in which is annexed, claim peculiar attention, as well on account of their being in immediate contact with each other, as because their situation in a schistose country, seems almost the only circumstance decidedly common to both. In almost every thing that respects their veins, it would perhaps be difficult to point out two mines more completely at variance, except that in each there occurs one of that denomination which is termed a contre.
Most of the east and west or metalliferous veins of Herland and Drannack mines varied from 2 to 6 inches in width, and whenever found to exceed the latter size, it proved an indication that they were about to diminish, and in the language of the miner, to pass away in the run of some fathoms in mere strings—a circumstance of extremely rare occurrence in the veins of Cornwall: they were consequently abandoned, because they no longer paid the expense of pursuing them east or west. It may well be supposed that considering the narrowness of these veins they were extremely rich; in fact they were so rich that it was frequently the practice of the miner, after taking away one side of the vein, to spread canvas to receive the load. That vein called the Manor Old Load exceeded the rest in width, being in the largest parts from one foot to one foot and a half in width, and the ore was occasionally found in floors of two or three feet wide, a circumstance more common in tin loads than in those of copper.
The direction of the contre is somewhat to the north of the west and south of the east: it produced a considerable quantity of copper ore, and varied from one to three feet in width. Near the surface great quantities of blende and iron pyrites were found in it. Wherever it intersected the east and west veins, their contents formed together one load at the junction for about eight fathoms in length and three or four in width. That part of the contre west of the cross vein called the Privateer Flucan was heaved by it northwards two or three fathoms, and the substances of both were mingled together. By Harvie's cross course it was heaved eight fathoms, and the substance of the cross course between the divided parts of the contre was found to be nearly twice its usual size, and consisted not of quartz only but of quartz mingled with iron pyrites, blende and copper ore, so that both the cross course and the contre in part lost their peculiar characters. The contre continued both N.W. and S.E. beyond its working, but was poor.
The substances of the numerous north and south veins or cross courses of these mines were quartz or flucan, or both. By the ground plan some variations will be observed in their directions, as being more or less to the west of north and south of east: it will also be seen that, their general effect is to alter the course of the veins they traverse, by heaving, in the phrase of the miner, the western parts of them higher north, but with some exception, for the reverse was the fact in respect to those parts of the Manor Old Load and Middle Mine Load traversed by Chambers's Flucan and the Great Cross Course.
The discovery of silver in one of the north and south veins of these mines has already been made known by the publication of Mr. Hitchins's paper on that subject in the Philosophical Transactions. It may however not be amiss to take some notice of that peculiar circumstance. It was found in that part of Convocation Cross Course which traversed the Manor Old Load, and was first noticed at about 116 fathoms from the surface: the Cross Course was at that place about 212 feet wide, but was narrower above, and consisted of quartz accompanied by a continuous flucan, which also was found with the silver. For some fathoms in depth after the first discovery of the silver, the Cross Course consisted for about 8 or 9 feet, and in some places for 3 fathoms, north and south of its junction with the Manor Old Load, of silver mingled with sulphuret of lead, iron pyrites, bismuth, cobalt, wolfram, &c. and these substances continued to abound and to traverse the copper load so long as it was rich while in contact with the cross vein.
It was noticed in the paper of Mr. Hitchins above alluded to, that the Rusty Cross Course, next on the east to Convocation Cross Course, also produced some silver, although not in sufficient quantity to pay the expenses of procuring it. This cross course consisted of quartz accompanied by a vein of flucan, sometimes on one side of it and sometimes on the other, together with iron pyrites occasionally.
The extent north and south of the channel of porphyry, or, to use the miners term, of elvan, which forms so conspicuous a feature in the section of Pleasure, Fancy and North Herland veins, is not known. Its effect in compressing the east and west veins is worthy of attention, and is noted on the ground plan, which, together with the accompanying sections are given from original documents now in my possession.
Section of Pleasure, Fancy, and North Herland Copper Mines.
The mines united under the name of Herland and Drannack were formerly worked separately, but were united on account of the drawing of the water being performed by the engines on Herland mine, and the name Drannack was added to Herland because two of the Mines (Fanny and North Herland) united with it were situated in a tenement of that name. This section therefore is that of the workings of the veins designated on the ground plan by the names of Pleasure, Fancy, and North Herland, north, middle and south branches. It is on the course of those veins, and supposes the country on the south side of them to be taken away, and of course in looking at this section we look north.
The shafts and levels which constituted the workings of these mines are not laid down, because they were not completed on the original, and even had they been so the present object can be as well accomplished without them. This section, together with the accompanying section of Herland mine, exhibits several striking geological facts.
By this section the underlie of the several north and south veins, or cross courses and flucans, which intersected the mines, will be observed.
It will also be seen that, to use the miners language, a large channel of elvan took its course with a very quick underlie towards the west: near the surface it was about 15 fathoms thick, but diminished gradually in depth. Its precise direction or extent on the surface towards the north and south was not ascertained. From some specimens of this channel in my possession, and of that passing through Herland mine, they appear to consist of crystals of quartz and felspar imbedded in compact felspar, which in one or two instances is mingled with compact quartz.
It merits particular notice that the substance of each cross course (viz. quartz) uniformly traversed the channel of elvan, but, while in it was much smaller and more compact than when in the schist. That of the flucans, which consisted, when in the schist, of two veins of flucan or soft marl with portions of schist between them, were while in the elvan very much smaller, and their substance appeared to be either a mere seam of flucan, or was of a sandy nature resembling pulverized porphyry.
The metalliferous veins likewise passed through the channel of porphyry, which had no other effect upon them than that of diminishing the load in size; it therefore appeared to be richer.
The north and south vein, called Convocation Cross Course, was not found to produce any silver in this mine.
Section of the Miner Old Vein.
This section is on the course of the vein called the Manor Old Vein, on the ground plan of Herland and Drannack mines. It was originally worked as a separate mine, under the name of Herland. Its greatest depth was about 150 fathoms from the surface.
The several cross courses and flucans correspond with those in the ground plan. Halfpenny Little Flucan and Chambers's Flucan, were nearly, if not quite, perpendicular to the horizon; the underlie of the others will be seen. It will be observed on consulting the ground plan, that Williams's or Penberthie's flucan traversed the veins both of this mine and that of Pleasure, Fancy, and North Herland mines. North and South veins generally take the name of the shaft they most nearly approach. The flucan in this mine was nearest to a shaft called Williams's, and therefore obtained the name of Williams's flucan. In the other, it approached nearest to Penberthie's shaft, and was therefore called Penberthie's flucan. Both names are therefore given on the ground plan.
It was in this mine, as has been already noticed, that silver was discovered in Convocation Cross Course, as well as a very small quantity in Rusty Cross Course.
One channel[errata 1] of porphyry also occurred in this mine; their effect on the N. and S. and E. and W. veins was similar to that produced by a channel of the same description in Pleasure, Fancy, and North Herland mine; their underlie and thickness are also about the same.
The underlie of the Slide is in the same direction as that of the channel of porphyry, but not so quick. Its substance was flucan of three or four inches in thickness; it passed through the cross courses and flucans. It also traversed the metalliferous vein, the course of which it interrupted, and heaved about fifteen inches, but whether to the north or south I know not. The load of the metalliferous vein was found to be richest a fathom or two along the run of the slide, both above and beneath it.
Transverse or North and South Section of Tin Craft Mine.
Tin Croft mine has been worked many years; and has yielded large profit both to the lord of the soil and to the adventurers. It was first worked for tin, principally, I believe, if not wholly, on the two most northerly veins. The country in which the mine is situate is for the most part schistose, but some remarkable alternations of schist and granite were discovered while working the two veins on the south, the probable cause of which appears to be this, that as these veins run parallel with and at the foot of the hill called Carn-brae, which is wholly of granite, the irregularities in the granite were supplied by a deposition of the schist. In no other part of the mine does granite appear, except that in following down two of the veins, as is noted on the accompanying section, they were found to traverse a mass of it at about 73 fathoms from the surface, above and beneath which schist only was observed.
The veins of this mine are worthy of attention in regard to their number, underlie, dimensions, and contents. In number they are seven; the other two may rather be called off-sets from a vein than veins. If however they be considered as veins, there are in this mine five of copper, three of tin, and one of tin and copper, in about a furlong and half of country from north to south. The general irregularities of their underlie, both individual and regarding each other, are very remarkable: only the Old Tin vein and Bodilly's vein proceed in a straight line, and it will be noticed that the New Tin vein proceeds in five directions, the second more inclining to the perpendicular than the first, the third more than the second, and so on. The South vein varies in width from one to six feet, and was rich in copper from about 35 fathoms until about 70 fathoms from the surface; that is, through the lower part of the upper deposition of granite, and the subjacent schist; but at about the place where it entered the granite again it was hard and poor. It was pursued for about 100 fathoms in depth. The ore was a mixture of yellow and grey, and like that of every other vein in the mine, was so extremely bunchy, that a regular course of ore, as it is technically termed, could scarcely be said to have existed in any part of it. Dunkin's vein varied from one to twelve feet in width, and its general underlie differed so little from the perpendicular, that advantage was taken of that circumstance to sink the shaft on its course. It was poor at the points of junction with Martin's and Bodilly's veins, but some ore was found in it between them. It was richer below the latter, and was worked to the depth of about 125 fathoms from the surface. Martin's vein was from about 3 to 6 feet wide, and yielded abundance of yellow ore (from which brilliant specimens were selected in tetrahedral crystals of considerable size) and was worked to about 100 fathoms from the surface. Bodilly's vein varied from one to six feet in width, the ore was yellow, the vein was for the most part poor and hard, and was worked to the depth of about 125 fathoms. The load, or substance, of the South and Dunkin's veins, passed through the New Tin vein, which, a little below the latter of them, yielded a considerable quantity of tin, as it did also at about 70 fathoms from the surface; in the intermediate space it likewise yielded tin, with a very small quantity of copper, but was far from rich. It was pursued for about 90 fathoms in depth. In the small vein on the south of Chapple's vein some tin was found, but the quantity was not considerable. Chapple's vein varied from one to three feet in width, and yielded yellow copper ore, interspersed with large quantities of iron pyrites. It was worked to about 100 fathoms from the surface, as was also the Highburrow vein, which varied from six to twelve feet in width, and yielded both tin and copper, either intermixed or running side by side down the vein: the latter was both yellow and grey, and very abundant. The old vein is very large, and was very productive of tin for about the depth of 45 fathoms from the surface, when it became poor, and was found to contain little else than iron pyrites. But as this vein, during many years, proved immensely rich in copper when passing through Cook's Kitchen mine, which is contiguous to Tin Croft on the west, little doubt is entertained by miners that it will also be found rich in copper at a greater depth than it has hitherto been proved in this mine. To Captain Thomas Teague, of Redruth, an experienced and very intelligent miner, and who during many years has principally conducted the working of Tin Croft mine, I am indebted for the Section. He informed me that in some part of Dunkin's vein, granite was found on one side of it and schist on the other, and that detached masses of each substance were found both in it and in the South vein; and frequently, that where granite formed the country on each side of the vein, the masses were of schist, and vice versa.
Description of some of the Veins in the Mines called Tol Carn, Huel Jewel, and Huel Damsel, near St. Die.
The veins of these mines are remarkable in several respects. A small brook was the boundary between Huel Jewel, which had been worked about fifty years at an immense profit, and that of an untried mine called Tol Carn, near St. Die. The veins of Huel Jewel were very rich in those parts which adjoined Tol Carn mine. This, of course, raised the expectation of the adventurers in the latter to an extraordinary pitch, and they set to work in the full belief that they should be at little trouble and expense in realizing on their side the brook, a continuation of the riches on the other side, as the veins of Huel Jewel made immediately for Tol Carn mine. On sinking a shaft in order to cut one of them at a certain depth, they were surprised at not doing so, since from knowing the precise run of the vein, the miner is generally able to make nice calculations in point of depth and distance in the sinking a shaft. After this had been done, as far as it was deemed proper, they drove through the country, at right angles with the shaft, from north to south, several fathoms without finding the vein. It was then attempted, by sinking shafts, to cut the other two veins which formed a part of the workings of Huel Jewel, but without success. After much labour and expense had been bestowed, it was discovered that underneath the brook forming the boundary between the two mines ran a cross vein of flucan, varying from a few inches to a few feet in thickness; this vein is believed to run quite across the country from sea to sea, heaving, in the phrase of the miner, all those parts of the veins, which it is known to intersect, on the western side of it, higher north than those on the eastern side; so that those parts of the veins in Tol Cam mine had been heaved by it full eighty fathoms higher north than the other parts of them in Huel Jewel, which however were found to correspond with those in Tol Carn not only in their respective distances but also in dimension. One circumstance however that added materially to the strange consequences of the cross vein was, that although the veins in Huel Jewel were rich quite to the cross vein, those in Tol Cam mine were almost without a speck of ore in them: it was therefore abandoned after a great expense, and consequently a great loss has been incurred.
Parallel with the veins of Tol Carn mine, but on the south of it, run the veins of the rich copper mine called Huel Damsel; these have not, I believe, been wrought quite home to the Great Cross vein. By the annexed ground plan it will be seen that a vein of flucan, varying from 2 inches to 2 feet in thickness, but without any perceptible underlie, that is to say, going down in a direction about perpendicular to the horizon, ran nearly north-east and south-west, intersecting the veins of Huel Jewel, the Great Cross vein, and the veins of Huel Damsel, and, to use the miner's phrase, heaving them, in the directions laid down in the plan about two fathoms from their strait courses. This vein is by the miner called a flucan.
It should be noticed that in the working of the above mines, their veins were discovered to be intersected near the Great Cross vein apparently by two or three smaller cross veins, between which parts of the east and west veins have been seen; as however the Great Cross vein is known in other parts of it to divide into branches (a circumstance very common in veins of this description) it is believed that these small veins are only branches of the large one. The whole of these mines are situated in granite.
Ground Plan of some of the Veins in the Copper Mine called Huel Alfred.
This mine is situated on a schistose hill, in the parish of Phillack, about three miles south-east of Hayle Copper-house. It had been worked previously to the year 1800, but was abandoned principally on account of the surrounding country having fallen in, and filled up or destroyed the only shaft that had been sunk. This circumstance was, most probably, the cause to which the successful working of the mine may be attributed. For, being compelled to sink another shaft, it so happened that the chosen spot was immediately above a vast body of ore which has never failed since its discovery. But as copper ore had been left at the bottom of the shaft that had fallen in, a level was carried to that place; it was however found to be a mere bunch, which circumstance, it is most probable would have deterred the miner from an effectual search after the great riches pitched upon by sinking the new shaft about 100 fathoms west of the former one.
Notwithstanding Huel Alfred is one of the richest and most profitable copper mines that Cornwall has now to boast of, a particular description of some of its veins would not have been now attempted, but for some circumstances worthy of particular notice, viz. that one of its veins is of that description termed a contre, remarkable for its magnitude and riches as well as its direction, and on account of the effects produced by its traversing an east to west vein, and a north and south vein, or cross course.
Both the shafts above alluded to were sunk on the contre, the direction of which is 28 degrees south of east and north of west. It varies from 9 to 24 feet in width, its underlie is 2 feet in a fathom to the east of north. At a small depth this bore the appellation of a ‘Flucany Load.’ Flucan prevailed very much between the depth of 50 and 70 fathoms from the surface, and burst out occasionally with such vehemence as to drive away the workmen. Captain Samuel Grose, an intelligent captain of the mine, informed me that he was once carried away 7 fathoms by its sudden irruption. But little flucan was seen at much greater depth. Beneath it and above the copper very great abundance of sulphuret and carbonate of lead occurred, together with iron pyrites, blende and quartz. The greatest extent to which the contre has been worked is 160 fathoms from its junction with the east and west vein towards the south east; 90 fathoms of which, at about 130 from the surface, are good ore. The only place at which the contre was rich when in contact with the east and west vein, was at about 117 fathoms from the surface. North-west of its junction with that vein the contre was small, and for more than 100 fathoms in depth consisted of strings of flucan, but at about the depth of 120 fathoms it enlarged to twelve feet in width and yielded some ore, mingled with fluor, blende, and iron pyrites in abundance; at 130 fathoms in depth, it was poor for 20 fathoms from its junction with the east and west vein, and then succeeded 40 fathoms of what the miner terms orey ground.
It seems to be the opinion of a very intelligent and experienced miner, Captain John Davey, who was a captain in Herland mine, and is now the managing captain of Huel Alfred, that the contre of the latter is a continuation of that of Herland.
The east and west, or regular metalliferous vein averages about 212 feet in width, and runs 10 degrees south of east and north of west: it underlies 212 feet in a fathom towards the north. The ore was about 110 fathoms in length east of its junction with the contre, but the east and west vein is poor every where when in contact with it, except at the only place at which also the contre is rich, viz. at about 117 fathoms from the surface.
West of the contre the east and west vein is lost for nearly 90 fathoms; and when discovered again, it varies from 18 inches to 4 feet in width and its load was found chiefly to consist of flucan with some blende.
The ore of the contre is yellow and occasionally compact, but it is for the most part approaching to black externally; and where richest, is loosely intermingled with small portions of quartz, blende, and iron pyrites, which prevailed very much near the surface.
The ore of the regular vein east of the junction with the contre is also yellow, and for the most part hard; but it is occasionally loose.
The common effect of a cross or north and south vein is that it passes through the cast and west or metalliferous vein, and mostly alters its course, of which numerous instances are shewn on the ground plan of Herland, Drannack and Prince George Mines. A cross vein occurs in Huel Alfred; its effect on the east and west vein is not yet known, but a rare exception to the general rule of north and south veins traversing metalliferous veins is here exhibited, for the load of the contre, which, as has been said, is rich in copper, not only passes through the north and south vein, but also heaves it out of its regular direction four fathoms. This is the only instance of the kind that has come to my knowledge. On consulting the ground plan of Herland and Drannack mines, it will be seen that the effect of the cross vein on the contre in that mine was exactly that of the contre on the cross vein in Huel Alfred.
The run of the cross vein is direct north and south; it underlies west about one foot in a fathom; is nine feet wide, and close to the contre (where only it has been seen) is chiefly filled with quartz, accompanied by blende and carbonate of lead in very small quantities, but in it there is no flucan; at and below forty fathoms from the surface, the quartz assumed the form of a fine sand, and the water from the cross vein was so powerful as to wash the sand 90 fathoms into the contre, so as occasionally to choak the pumps. It should be remarked that no ore was seen in the latter while passing through the cross vein for more than 100 fathoms from the surface.
About 45,000 tons of copper ore, the produce of Huel Alfred, have been sold since the beginning of 1801, for the sum of about £350,000. The number of men women and children, employed underground and on the surface, amounts nearly to 1500. There are three large steam engines for drawing the water, and two steam whims for drawing the ore, now on the mine. The monthly expenses for labour, coals, ropes, timber, &c. amounts now to about £5300. The profit hitherto divided amongst the adventurers amounts to about £120,000.
- ↑ I have been at some pains to discover the original meaning of the term lode, or load, as the technical appellation of the east and west, or metalliferous veins of Cornwall. Borlase in his natural history of the county treats at page 146 of the Fissure, and the next chapter begins thus: 'From the Fissures let us proceed to that which they contain, whatever fills them, we call a lead;' making a distinction between the fissure or vein and the substances it contains. He says in the same chapser 'where the load is barren, it may serve to lead us to what is rich;' and in a note, concludes the term lode to be an old Anglo-Saxon word, meaning lead; thus load-stone, meaning leading-stone,' and refers to Lye's Junius ad verbum. Without going so far back for an authority which nevertheless may be correct, I am induced to believe the term lode, though thus spelt by Borlase and Price, originally meant the burthen or load of the metalliferous vein. Carew, whose ‘survey’ was published almost a century ago, not only spells it, but at p. 8, in speaking of the effects of the flood on the rocks of the county, says it carried away so much of the ‘ load as was contained therein.’ Besides it is to be noticed, that the north and south veins, which are not metalliferous, are uniformly termed courses, making a clear technical distinction between unproductive and metalliferous veins.
- ↑ I have used the word Country in the sense in which it is employed by the miner, and shall hereafter so use it, conceiving it to be well adapted, if not better than any other I have been able to find, to convey the intended idea. If a miner be driving an adit North and South, or in any other direction than that of the Load, he says he is “driving through the country.”
- ↑ Ore is said to be discovered near the day, when it lies near the surface.
- ↑ Huel signifies a Mine, according to the Cornish-English Vocabulary of Borlase. It is commonly, though erroneously spelt, Wheal.
- ↑ Geological Transactions, vol.1.
- ↑ Grouan signifies Gravel, in the Cornish language, Borlase.—It seems therefore probable that Grouan, correctly speaking, is decomposed Granite.
- ↑ A rare exception (the only one I am acquainted with) has been found in the mine called Huel Alfred; a description of some of its veins is annexed.
- ↑ Min. Cornub. p. 50.
- ↑ Ibid. p. 50.
- ↑ “Whether tin doth grow again, and fill up places which have been formerly wrought away, or whether it only separateth itself from the consumed offal, hath been much controverted, and is not to this day decided.” And “whether-dead lodes—that have not one grain of tin in them—may not hereafter be impregnated, matured, and prove a future supply to the country, when the present lodes are exhausted, I think well deserves our highest consideration.” Notes to Carew's Survey of Cornwall, edit. 1811, by Tonkin, edited by Lord de Dunstanville. It must be confessed that these inquiries still prevail amongst practical miners.
- ↑ In reply to this observation, it has been said that the ores of some mines are found to smelt more easily when mingled with those of certain other mines than alone. This will not perhaps be doubted. All that is now contended against is, the common practice of mixing indiscriminately ores of copper of any, or rather of every description.
Errata