Towards the close of the last century native gold was accidentally found to occur, disseminated in the bed of the streams which descend from the northern flank of Croghan Kinshela, a mountain which lies on the confines of Wicklow and Wexford, and at the junction of the granitic ridge with the clay-slate. Considerable quantities of gold were collected by the people. It occurred in massive lumps, and in small pieces, down to the minutest grain. One piece weighed twenty-two ounces; another eighteen ounces; others nine and seven ounces. The gold was found accompanied by other metallic substances dispersed through a kind of stratum, composed of clay, sand, gravel, and fragments of rock, and covered by soil, which sometimes attained a very considerable depth (from twenty to fifty feet) in the bed and banks of the different streams. Shortly after the discovery of the occurrence of gold, the business of its extraction was taken up by the Government, under the management of Mr. Weaver and some others. The method followed was that usual in gold mining districts, of washing the clay or soil in vessels with water; the metal, from its great density, settles down, and the lighter earthy impurities
p.209are decanted. The valuable material is thus concentrated by a succession of washings, until finally the operators are enabled to pick out the particles of precious metal. The further operation of dissolving out with mercury the particles of gold too fine to be recognized by the eye, was, in some instances, had recourse to.
The total quantity of gold collected by the Government working, in about two years, was 945 ounces, which was sold for £3675; but the cost of the workings, and of various trials made in search of the original deposit of the gold, exceeded this return, and the workings having been interrupted, were not again resumed by Government. It has been calculated that at least £10,000 was paid to the country people for gold collected, before the Government took possession of the works.
This native gold is of a rich yellow colour, soft, and malleable. Its specific gravity is 19. An assay of 24 grains of it, effected by Mr. Weaver, gave pure gold 22.58, and silver 1.43. Another assay of it, by Mr. Alchorn, Assay Master in London, gave, for 24 grains, 21 3/4 fine gold, 17/8 silver, and three-eighths of a grain of an alloy of copper and iron.
The localities that have yielded gold in the largest quantity are Ballinvally, Ballintemple, and Killahurler, all situated in the same valley. The gold is associated with magnetic iron-stone, sometimes in masses of half a hundred weight; also iron pyrites, brown and red hematite, wolfram, manganese, and fragments of tin-stone in crystals, together with quartz. From the nature of these attendant minerals, of which most are known to occur in the quartz veins of the adjacent mountain, it was hoped that by tracing up the rivulets to their sources, and laying bare in various directions the underlying rock, the metalliferous veins might be discovered, from the disintegration of which the sand and soil of the bed of the streams had been produced. All such trials proved useless, and the question as to the source from whence the gold of those streams in Wicklow has been derived, remains still unanswered.
A few years since this district was leased to a London Company, under whose directions some workings were carried on in a very imperfect and trifling manner up to a short time
p.210since, when they were finally abandoned. Neither the intelligence nor the energy necessary for success in such undertakings appears to have been applied. It is questionable whether under any management this source of mineral wealth could be rendered profitable, and mines of the precious metals are certainly those which this country can best afford to do without.
In other localities in Wicklow particles of native gold have been found, as at Croghan Moira, at Ballycrea, and Ballynacapogue, but the quantities were too trifling to be an object of practical working.
There is no doubt but that sources of native gold were known to the Irish at a very remote period. The abundance of gold ornaments and weapons, which are so peculiar to this island, and for which no source by importation can be assigned, is sufficient evidence of this, as well as the evidence of our ancient writers, descriptive of the use and manufacture of this precious metal. That it was much more abundant here than in England is shewn by the fact mentioned in Delarnes' History of Caen, that when, after the Norman conquest of the British Islands, treasure was exacted from both to the exchequer of Normandy, the tribute exacted from England was 23730 marcs of silver, but from Ireland 400 marcs of silver and 400 ounces of gold, an enormous quantity for those times.
Native silver has also been found in Wicklow in a bed of iron ochre in the upper ground of Cronebane. The particles were seldom so large as to be visible to the eye, but the silver was extracted by fusion with lead, and subsequent cupellation. It was auriferous, containing thirty grains of gold in each ounce. This deposit has been long since exhausted.
The occurrence of tinstone in Ireland is of very considerable importance, as this metal, indispensable in the arts, and of high price, is one of the most valuable elements of mineral industry. Hitherto it has been found, however, only disseminated through the auriferous soil of Wicklow; no veins or workable deposits of it having been met with.
Of the remaining metals of practical importance many have been found, and in some cases their mines have been worked in Ireland, but they have not attained much development
p.211hitherto. The oxide of manganese occurs at Howth in the vicinity of Dublin, in Wicklow, but more especially at Glandore, on the southern coast of Cork, where considerable quantities of the ore have been raised. In the Glandore mine, the principal variety of ore is the true peroxide; the hydrated sesquioxide is also found. The ore occurs associated with veins of quartz. The rock of the locality itself is the upper clay-slate, of which so much of the mining district of the south of Ireland is composed. The earthy hydrated peroxide of manganese is of very common occurrence, but I do not know any locality in in which its quantity or its quality would require special notice.
An ore of antimony is found in Clare associated with the lead ore of the mines described in page 201, which is of interest as a source of that important metal, and also that in composition it differs from the usual ores, being a new mineral, and named Kilbrickenite by Dr. Apjohn, who analysed it. It consists of sulphuret of antimony united to sulphuret of lead, and it is remarkable, that the two metals are here naturally united in the same proportions as they are in manufacturing printing types, so that this ore, when smelted, should give a natural type metal.
The ordinary ore of antimony, the grey sulphuret, has been found near Clontibret in Armagh, where it forms a vein about four inches thick, in the clay-slate rock of the district. Some desultory attempts have been made to utilize this deposit of antimony, but, so far as I understand, without much profit.
The curious history of the occurrence of Cobalt ore, at Killarney, has been given in page 187. No where else has it been found in quantity, though traces of it occur in all the mining districts. The minerals of nickel, chrome, arsenic, and bismuth, have been found, but have not been hitherto the objects of industrial enterprize. One of the ores of zinc, the sulphuret, or blende, is a common associate of the veins of lead and copper ore, and is intermixed sometimes in large quantity with the iron pyrites, worked in the Wicklow district for the manufacture of sulphur and sulphuric acid, but no deposits of the zinc ore, sufficient in extent and purity, to enable the metal
p.212to be extracted, have been as yet found, though the circumstances of this country lead to a confident expectation of their being yet discovered. From the impure blende of the Wicklow district could be easily prepared the sulphate of zinc or white vitriol. The process consists in roasting the mineral in kilns or furnaces, for which its own combustion supplies nearly the necessary heat. The product is lixiviated with water, and by treating successive quantities of mineral with the same portion of water, the liquor may be obtained so concentrated, that it requires very little evaporation to enable it to crystallize.
It has been mentioned in the general description of the Wicklow clay-slate district, that the copper lodes are associated with vast beds of bisulphuret of iron, which rendered the extraction of the more valuable ore difficult and expensive. This iron pyrites, which, when pure, is of a very pale yellow colour, is so hard as to strike fire with steel, and crystallizes in cubes and octohedrons, consists in 100 parts of
Iron . . . 46.67
Sulphur . . . 53.33
When it is heated in close vessels it gives off a third of the sulphur which is contains, and the residue, which is dark grey, and is called magnetic pyrites, consists of
Iron . . . 56.76
Sulphur . . . 43.24
This residual sulphuret, when exposed to the air and moisture, rapidly decomposes, absorbing oxygen and forming sulphuric acid and oxide of iron, so that on washing it, a solution of green sulphate of iron (copperas) is obtained, from which the salt may be had in crystals.
If the iron pyrites be heated in a current of air, all the sulphur which it contains may be burned out as sulphurous acid gas, and the iron will remain in the state of red oxide. As the mineral is itself combustible, it may be burned in a kiln,
p.213the exhausted portions being extracted from the bottom, and the fresh ore introduced at the top. In this way the sulphur contained in it may be made available in the manufacture of oil of vitriol, and indeed in every case where ordinary sulphur would be burned.
To all these uses the iron pyrites had long been devoted in the north and east of Europe, but in this country it had been considered not merely valueless, but absolutely an impediment to the working of the copper mines. About eight years since, however, the mineral suddenly became important. The Government of Naples placed an exorbitant price on the sulphur, with which the manufacturers of England had previously been supplied from the volcanic districts of Sicily, and being driven to obtain a substitute at a cheaper rate, they had recourse to the deposits of iron pyrites in Wicklow.
The mines which produce the iron pyrites, are those of Ballymurtagh, Ballygahan, Tigrony, Cronebane, and Connoree, they all contain the same sulphur course, as it is termed by the miners, which traverses them in a north-eastern and south-western direction. This mineral occurs immediately at the surface, and is raised in large quantities down to the depth of fifty feet, the lode varying in width from four to thirty-six feet, and in bunches according to the purity of the ore.
The iron pyrites is indeed seldom absolutely pure; besides an intermixture of clay-slate or other rock in various proportions, it is associated with other metallic sulphurets in small quantity, and frequently with the arseniuret of iron or arsenical pyrites. These impurities influence the value, and the products, of the sulphur ore in a very sensible degree. Thus the presence of copper renders it more valuable. Mr. Barnes, in his letters on this district, shews, that the sulphur and copper ores are in no way distinct, but graduate insensibly into each other. Thus the copper ore of Ballymurtagh contains at least 30 per cent. of sulphur ore, and the greater part of the pyrites workings in the same mine, contains about 2½ per cent. of copper. The presence of from ½ to 1 per cent. of copper in the sulphur ore of commerce is not unusual. When this ore is burned in the kilns for the manufacture of sulphuric acid,
p.214the sulphuret of copper passes by oxidizement, to sulphate of copper, which may be extracted by lixiviating the slags with water, and either crystallized, or as is more usual, decomposed by fragments of old iron, and the copper precipitated in the metallic state. When the ore contains sulphuret of zinc, this forms by the roasting, sulphate of zinc, which may be similarly extracted and crystallized. The presence of the arsenical iron is very injurious, for owing to the volatility of the arsenic, which accompanies the sulphur in all its stages of manufacture, the iron pyrites becomes unfit for the preparation of sulphur or sulphuric acid, wherever those bodies are to be applied to form medicinal substances, or that they are required pure for chemical uses; but it is yet perfectly applicable for all manufacturing and technical uses, and although the price of the Sicilian sulphur has now fallen very low, the pyrites trade has by no means diminished in proportion.
During the interruption of the Sicilian trade, the quantity of pyrites annually exported from the Wicklow district, is considered to have reached 100,000 tons. It is now, however, considerably less.
The returns given in page 178 for the produce in copper ore and pyrites of the Ballymurtagh mine enable a general idea to be formed of the present extent of this branch of mining. It is highly gratifying, that the favourable position in which the mines of the Avoca valley were placed by the force of the sulphur monopoly in Naples, has been sustained up to the present day by the judicious enterprize of the proprietors, and the steady improvement of the produce.
Mr. Roper states the number of persons employed in this district to be about 2000, and that from 500 to 1000 carts are daily employed in bringing the ore to Wicklow and to Arklow for exportation.
I have mentioned that when the bisulphuret of iron is heated to redness, one-third of its sulphur is given off, and the iron remains as magnetic sulphuret, which by exposure to the air absorbs oxygen and forms green copperas. This application of pyrites is of extensive use on the Continent of Europe. It may be carried on in a variety of ways. The pyrites may be distilled
p.215in retorts of earthen ware, like those used in some gas works, or the ore may be burned in kilns, to which only a limited supply of air is admitted, so that one part of the sulphur being burned, the heat evolved suffices to distill off the rest, and the sulphurous fumes being conducted into large brickwork chambers, the sulphur is deposited whilst the sulphurous acid gas passes off to the vitriol chamber, where it also is economized. Where this process has been tried in this country, much disappointment has occurred from not using pure pyrites, and from the belief, that the pyrites should lose half its sulphur, whilst it really gives off but a third. A ton of pure iron pyrites gives by distillation 3.6 cwt. of sulphur. But if a ton of the good sulphur ore of commerce be taken, which does not contain more than 75 per cent. of the pyrites, the produce of sulphur, on distilling it, will be only 2.7 cwt., and the impure ore requires a higher temperature, causes more loss of apparatus, and leaves a much more intractable residue. Hence this process can only be profitably carried on, where the pyrites available is found almost absolutely pure.
In speaking of the copper and lead district at Silvermines in Tipperary, I have noticed the immense vein of iron pyrites which is there found, but the inland situation of which prevented its being worked by the Mining Company of Ireland. In the case of our domestic industry becoming active, the sulphur ore of that locality, from its proximity to the Shannon, may be available throughout a very extensive range of country.
The bisulphuret of iron is met with in another and totally different geological position, that of the coal formation, where it occurs so abundantly intermixed with the coal, and in the shales above, as to prove often seriously detrimental to the quality of the fuel. This pyrites oxidizes much more rapidly, on exposure to the air, than the pyrites of the primitive clay-slate or other older rocks, so much so, that the masses of it become in a short time coated with a crystalline covering of green copperas. In the Drumglass collieries, Tyrone, this oxidizable pyrites is peculiarly abundant, and there, as well as in the collieries of the Leinster district, it would only be necessary, in order to manufacture copperas from it, to collect
p.216the pyrites into a heap, and in dry weather to wet it occasionally. The liquor which would drain off being conducted to a tank, should be allowed to digest on some old iron to neutralize the excess of acid, and by a moderate evaporation, the salt could be obtained crystallized. This is the plan adopted in England and Scotland where copperas is manufactured, and there is nothing to prevent the same process being successfully carried on with us. In the Munster coal field there is also abundance of this oxidizable pyrites, which by its spontaneous decomposition in many places, impregnates the waters with iron. The reaction of these products on the soft slaty rocks of the coal strata, gives origin to other bodies, of which some are of considerable practical importance, as they afford the materials for the manufacture of alum, and of these it will be necessary to speak with some detail.
Alum is manufactured in England, either naturally, as it is termed, or artificially. The latter is a process which consists in decomposing pure clay with sulphuric acid, and adding then the alcali, which may be either potash or ammonia. The alum so made is crystallized in the usual way. The only objection to this process is, that the sulphuric acid has to be first manufactured, which is costly. The natural alum is made at Whitby, where the upper shales of the coal formation contain pyrites in abundance, together with some coaly matter. This alum slate, as it is termed, is formed into great heaps with brushwood, and the whole set on fire. A very slow combustion is kept up for some weeks, the sulphur of the pyrites reacts on the alumina of the clay, and on lixiviating the roasted mass sulphate of alumina dissolves. The alcali is then added, and the crystallization of the alum is effected in the usual manner. Near Glasgow, the alum is made similarly from the soft pyritic shales of the exhausted coal pits, the process followed being absolutely the same in all its general features. Now there is no requisite for the preparation of alum on the other side of the channel, which we do not possess here in those localities of oxidizable pyrites, which I have just enumerated; but it is remarkable, that we are even more favourably circumstanced, for a formation of true alum slate presents itself
p.217on the western coast of Ireland, more extensive than that in Yorkshire, indeed, as Mr. Ainsworth says, the most extensive that is to be found in Europe.
This slate forms the upper layers of the great Munster coal formation, the superficial extent of which has been already noticed. Its section, presented to the Atlantic for a distance of forty miles from Ballyvaughan in Clare, to Ballybunion in Kerry, offers a series of frowning precipices and deep caverns. The softness of some portions of the rock, allowing the ocean, which on that coast rages in all its vigour, to undercut the cliffs, and work out from between the layers of harder strata, passages and caves, which present scenes of singular beauty and grandeur. Along this coast the pyrites with which these shales abound, produce, by gradual oxidizement, copperas, and by its action on the material of the rock, native alum. Mr. Ainsworth, who published a very full account of one of the most curious localities on this coast, the caves of Ballybunion, describes the structure of the alum cliffs, in words of which the following may serve as an example: In Dune Bay, the upper stratum of the cliff is composed entirely of very anthracitous alum-slate in thin laminae, which are divided by parallel and transverse veins of crystallized alum, the same mineral occurring in nodules, efflorescences, and in loose powder, in the more decomposed beds, often contaminated by shades of yellow and red. In the small cave beyond, copper pyrites abounds, accompanied by arsenical iron, and in the cavities another combination of alum with sulphuric acid, and a mineral alkali.
Mr. Ainsworth found at Ballybunion, and along the coast, various aluminous minerals, which he describes as follows:
True alum, in powdery and capillary efflorescences, and in globular concretions.
The basic alum, or aluminite, in abundance.
The iron alum, or hair salt, similar to that found in the alum pits at Hurlet, near Glasgow.
Sulphate of iron and sulphate of copper were found in efflorescences on the surface of the rocks. Iron pyrites exists in abundance in the generality of the cliffs and rocks. Copper pyrites was found, and also, but rarely, arseniuret of iron.
It is possible that the enthusiasm of Mr. Ainsworth has given a colouring to his descriptions of these aluminous shales, of which some of the very brilliant tints may become sobered under more practical examination. Certainly, although profoundly scientific in his phraseology, the chemical nature of the bodies he describes cannot be considered as independent of future analyses; as Dr. Scouler has ascertained that a mineral, which Ainsworth announced as a new kind of alum, is nothing more than common gypsum, sulphate of lime. Nevertheless, the general characters of this district are decisive as to its capabilities for all branches of the manufacture of alum and copperas. The abundance of turf and coal makes fuel cheap, whilst the Shannon, by which it is intersected, gives it communication with the interior of the country, and affords the most favourable means of access to foreign and domestic markets. Nearly two centuries ago, alum and copperas were manufactured at Tralee and elsewhere in this district by Petty, Blennerhasset, and others, and the soft slate containing copperas, was administered as a medicine, and is described by many old medical writers, under the name of Lapis Hibernicus.
Clay in its purest form, and in the chemical sense, is produced from the gradual decomposition of the felspar contained in the various granitic rocks, by the action of water and of the atmosphere. The composition of the felspar has been stated in page 162. The potash which it contains is washed out in combination with the greater part of the silica, and there remains a fine light powder, which is pure clay. Its colour is perfectly white, which it preserves when most intensely ignited. It is absolutely infusible. These qualities identify the pure porcelain clay. In England the granitic district of Cornwall is the source of the pure clays used in the potteries of Staffordshire; in France, the granitic rocks of Limoges; in Germany, those of the Riesengebirge. The composition of the porcelain clay, or as it is often called by its Chinese name, Kaolin, maybe expressed by the chemical formula, 3 Al2O3 + 4 SiO3 + 6 HO, which gives:
p.219Silica . . . 47.0
The clays of different localities vary very sensibly from this standard. They are mixed with traces of the undecomposed rocks and minerals which affect their composition; thus most clays contain traces of potash from feldspar, of which the decomposition has not been complete. Traces of lime and of iron arise from minerals accidentally present, which are very detrimental to the subsequent value of the clay, and often an excess of silica from the cotemporaneous degradation of the quartz, which is a principal ingredient of the granitic rock.
In all of the granitic districts of this country, beds are found where the felspar has been so completely decomposed, as to have produced clayey deposits. I possess masses of decomposed granite from Mourne, perfectly similar to that of the china-claystone of Cornwall. The agricultural soil of extensive tracts of Wicklow, Carlow, and Wexford, has been produced by this weathering of the granite; and at Kilranelagh, near Baltinglass, kaolin of fine quality has been obtained. At Tullow also, in Carlow, porcelain clay, not absolutely free from iron, however, exists in considerable quantity. It is not to be expected, however, that fine porcelain clay is to be found presenting itself on the surface of our granitic districts. Its preparation in Cornwall is strictly artificial. The blocks of decomposed granite are crushed and washed with water. The liquors, loaded with the fine particles of clay, are made to flow into reservoirs where this material is deposited, the clear water is run off, and the clay so obtained brought into commerce. No person has yet essayed the manufacture of china clay in this country; the materials for it appear from all evidence to exist abundantly.
In other places extensive deposits of clay occur, which, though not pure enough for the manufacture of fine porcelain, are yet excellently adapted for other uses. Mr. Griffith describes an extensive district of such clay occurring in Tipperary, between
p.220Cahir and Clonmel, which he considers equal to the pipe-clay of Bovey. It burns purely white, and in the extreme heat of a porcelain furnace only acquired a very slight buff tinge. Large quantities of this clay have been exported to England, but no use has ever been made of it at home. This clay, though on the edge of the coal district, lies in the cavities of the lower limestone; and just similarly circumstanced are several deposits of very pure clay which occur in Roscommon, some along the shores of Lough Ree, especially near St. John's Point, and others more inland, as at Kellymount. This clay has given origin to a local manufacture of tobacco pipes, of which from 500 to 1000 gross are made weekly. The wholesale price of these pipes is about one penny per dozen; they are very rudely formed, owing to the imperfect instruments used. If suitable tools, and some instructed workmen from Dublin, were to assist those local efforts, a considerable trade might be created, for the quality and colour of the clay are fully equal to any that we import, or that is used in the sister kingdom.
Although up to the present time no beds of absolutely white clay have been found in the tertiary formation of Lough Neagh, yet it is probable that future examinations will reveal such. The beds at Annaghmore, and in other places, of not less than seventeen feet in thickness, are found to become but slightly coloured on being calcined.
In an industrial point of view, however, there are no clay deposits more important than those of the coal formation, the necessity for which, along with the ore and fuel, for the manufacture of iron, has been already noticed (page 122). In all our coal fields the beds of coal rest on strata of clay of excellent quality, to the particular description of which I shall now proceed.
The Tyrone coal field contains numerous beds of clay, of that quality which, being infusible, is denominated fire-clay. In the Annagher colliery, each of the four coal beds worked rests on a bed of clay, from four to six feet thick; but deposits of similar clay occur nearer the surface, and it is obtained for the purposes of the brick and coarse pottery manufacture of
p.221Coal Island, by pits of about thirty feet in depth. It is a very strong, adhesive clay, fawn coloured, and burning reddish yellow. It is absolutely infusible, and makes fire-bricks, tiles, and crucibles, of the best quality. It is, as well in appearance as in properties, and in geological position, perfectly analogous to the clay of the Staffordshire district, so well known as Stourbridge clay. In order that the nature of the Coal Island clay may be decisively established, I made an accurate analysis of it, of which the following are the results, and for comparison I annex the composition of the two clays most esteemed for the manufacture of crucibles for making steel, and for fire-bricks, in England.
|Clay of||Coal Island||Stourbridge||Stannington|
|Peroxide of iron||8.4||0.0||Traces|
The analyses of the English clays are taken from a valuable Memoir on the Manufacture of Steel in England by M. Le Play, published in the Annales des Mines.
The presence of the oxide of iron in the clay of Tyrone gives the wares formed of it a buff or brown colour, which must always limit its use. The analyses shew that it contains just the same silica as the Stourbridge clay, and the sum of the oxide of iron and alumina is just equal to the alumina of the other.
In the Lough Allen coal field, beds of fire-clay are found, of which that forming the seat of the Crow coal varies from a few inches to three feet in thickness at the edges. In the valley of the Arigna this bed was found uniformly three feet thick, and of excellent quality, the whole of the bricks used at the iron works, by the original proprietors, having been made of it; and comparative experiments, described by Mr. Weld, as having been carried on in the Laboratory of the Royal Dublin
p.222Society between it and Stourbridge clay, having shewn it to be not inferior. Under the three foot coal lies another and similar bed.
Near Lough Allen, on the western base of Benbo Mountain, are found clays of various colours, red, yellow, black, and whitish, produced by the decomposition of the rocks. Considerable quantities of a whitish clay has been raised and used as fuller's earth. It feels soapy, and resembles decomposed steatite. It is mixed with iron pyrites.
In the Leinster coal field the coal beds rest on strata of clay, which I have found to contain a great deal of very finely comminuted mica, and some sand. When freed from these admixtures, it is a very pure, strongly adhesive clay, which burns almost perfectly white, and was infusible in the strongest heat of a wind furnace. Of this clay Mr. Griffith says: This fire-clay is of very fine quality, and is, in my opinion, superior to that of Stourbridge in Worcestershire; excellent fire-bricks have been made of it, but no manufacture to any extent has been attempted. Mr. Tighe, whose Statistical Survey of Kilkenny is so rich in facts, describes more fully the properties of this clay. He says:
The seat of the coal has properties which appear worthy of attention; it has been long used at Castlecomer for backs of grates, and is known to stand fire in a peculiar manner. Mr. Finlan, the late director of the steam engines, constructed by means of it a small reverberating furnace, in which he smelted iron, and made crucibles of it which stood the heat of the strongest fire. Mr. Whitmore Davis, the architect employed in building the new barracks at Castlecomer, made some experiments upon it which he communicated to the Dublin Society last year. He formed fire-bricks of it, of the very best quality, and he observes, that by pulverizing the coal seat, and making it into mortar, nothing can better stand the fire and answer all purposes for fireworks, as the more fire it gets, the harder it grows. This he affirms from repeated trials, and says he is convinced from the handsome colour it assumes, it will not only answer every purpose in earthen ware, but he hopes also, that of pots for glass-house purposes; and being
p.223convinced of the great utility of the coal seat in the fire, he made trial of it also in water, and found that when properly prepared, it would answer every purpose of terras; he made trials also of its utility as to external incrustation on walls, where it set firmly and has every reason to think will answer well. The best bricks made by Mr. Davis consisted of two parts of coal seat, and one of clay: a sixth part of sand being added, made them run too much: the coal seat which he used in building a brick cistern, was first calcined in a lime-kiln and then pulverized; it held water immediately in the most perfect manner. The coal seat in its natural state burned in a strong fire becomes white, and as hard as many silicious stones. Mr. Davis sent specimens to Dublin, which were examined by Mr. Higgins, who returned it as part of his opinion, that the coal seat would answer for porcelain, as one of the ingredients. Its uses under water appear more doubtful, for though pieces of it found in the stream of Castlecomer had become very hard in the water, they were also brittle, and perhaps would rather crack than set like terras, whose property of swelling in water depends upon the quantity of iron it contains, which becomes oxygenated by combining with the oxygen of the water. The coal seat appears to contain no iron, or a very trifling quantity: finely powdered and digested in marine acid, it did not lose quite a grain in an hundred of its weight: the solution gave no precipitation with volatile alkali, a very slight one indeed with prussiate of potash; but with pure potash it gave a little precipitation; by which it appears to contain a small quantity of calcareous earth: the remainder consisted, as near as it could be analized of 54 per cent. silex and 44 argill; and the colouring matter appeared to be carbon, in a small proportion. One hundred grains digested repeatedly in concentrated sulphuric acid, left forty-eight grains of silicious sand with a little carbon: the solution gave a white precipitate with volatile alkali; none with prussiate of potash. By another analysis one hundred grains appeared to contain 61 per cent. of silex, 36 of argill, the remaining three grains were carbon and calcareous earth, with an almost imperceptible quantity of iron. On the whole then it appears to contain
p.224a larger proportion of silex than of argill, and not enough of any other mineral to affect its qualities.
I have not myself analysed this clay of the Kilkenny coal beds, but the composition given by Mr. Tighe above, is remarkable, as being identical with that of pure Stourbridge clay, when dried. The proportions given in p. 221, when calculated without the water, are, silica 54.3, and alumina 45.7, practically identical with Mr. Tighe's of 54 and 46, and hence proving the excellent quality of the material.
Deposits of clay, which, though inferior in quality to those above described, are available for the manufacture of coarse pottery, of flooring and draining tiles, and of bricks, occur in almost every county in Ireland. Several in Kilkenny, along the edge of the coal district; in Wexford, near Gorey; in almost every parish of Tyrone; at Knock, in Meath; in Mayo; in Tory Island, off Donegal; near Celbridge, in Kildare.
Of a quality much superior to the common sort are whitish clays found near Cloyne, and at Youghal in the county of Cork, and at Calinafersey in Kerry. These are light coloured, strongly absorbent, and have been used by the peasantry as fuller's earth; when calcined they become a light yellowish red, and are very suitable to the manufacture, not merely of tiles and common pottery, but also of an excellent description of coloured earthenware. At Howth, associated with the limestone and dolomitic rocks, are extensive deposits of a very excellent clay, which burns nearly quite white and resists the most intense heat. This clay is worked into crucibles by Messrs. Mallet, for the various operations of their extensive foundry, and is found equal to the clay of Stourbridge; its quality is such as would render it excellent for delft and stoneware, to which object, however, it has not been applied.
I shall terminate this notice of the clays of Ireland, by reference to the mode of preparing them for their various uses, to which but very little attention has been hitherto paid. These clays, as dug up from the ground, contain universally disseminated through their mass, portions of organic matter, and also frequently iron pyrites. When such clay is calcined, these foreign matters are decomposed, and evolve gases, by which,
p.225bubbles and cracks are formed in the clay, and the soundness of the ware deteriorated. To avoid this, the potter in other countries stores up his clay for many months, or perhaps a year; he cuts it up and mixes it frequently, and exposes fresh surfaces to the air; the clay ferments, exhales a foetid odour, and at last all these organic and sulphury impurities become decomposed and pass off, and the clay is found very much improved in quality. The clay, as used in Ireland, is, on the contrary, injured by bad management. Clays of different beds are imperfectly mixed together; sand and pebbles are left intermixed with the clay, and hence, when bricks or tiles so made, are burned, they retract unequally, and become deformed in shape. Some parts vitrefy, whilst others remain unburned, and thus from clays which might produce excellent products, articles of very inferior value and low price alone can be obtained. In other countries the clay is diffused through water, and the sand and gravel having settled, the thick liquid is run into reservoirs, where the clay gradually deposits. This purified clay is worked in a pug mill, so that its quality becomes absolutely uniform, no matter how many different kinds may have been originally taken, and thus the articles fabricated, acquire a soundness of quality, and uniformity of texture, by which their price and the advantage to the artizan is materially enhanced.
Immediately in connexion with the clays, stand the other materials of the earthen ware, china and glass manufactures. Silica, in its various forms of flint, quartz, and sand. The chalk of Antrim contains abundance of flints. The great masses of quartz of Donegal and Mayo, the patches of it which appear in other places, forming Howth and Bray Head, and capping various mountains, afford unlimited supply of it, and though the general mass of the quartz rock is usually tinged by iron, yet veins of perfect whiteness occur sufficiently abundant for industrial uses.
The weathering of the quartz rock of the Muckish Mountain in Donegal, has given origin to a species of sand of singular purity. It is purely white, in rather large grains, and is chemically pure. If the approaches to that mountain were more
p.226easy, and that this kind of sand were brought into the market upon fair terms, there is no doubt but that it would be preferred to the sands of the south of England, none of which can at all compete with it in purity of colour and composition. In several of the bays of Donegal, the sands thrown up by the Atlantic storms is of great purity, and fully equal to that in ordinary use amongst glass manufacturers. Fine crystalline sand occurs at Lough Grana and at Lough Coutra, which is highly valued for the purposes of polishing and whetting.
The quantity of fuel consumed in the burning of porcelain and earthen ware, and in the melting of the materials of which glass consists, might appear to many persons to present a serious obstacle to the introduction of such occupations amongst us. Such is in reality not the case. The establishment of the potteries in Staffordshire, and the great developement of the manufacture of earthen ware in England, arose, not from the mere price of fuel, but from the energy and artistic taste of the illustrious Wedgewood. In fact, Staffordshire is very badly placed with regard to the materials of the ware, all of which are more important than the fuel. The china clay, the quartz, and granite, are brought from Cornwall, the second rate clay from Devon and Dorsetshire; the flints from Kent and Antrim. I have not been able to procure accurate returns of the cost of the coals employed in making the different kinds of earthen ware, but I am satisfied, from the analysis of the elements of the manufacture, that its influence must be comparatively small. Even in making glass, where certainly much more fuel is consumed than in forming the same value of stoneware or china, the proportion which it bears to the other elements of cost is not considerable.
From numerical facts of the circumstances of this trade, which were given to me by an extensive and intelligent manufacturer, I have calculated, that to produce a ton of finished flint glass, there are required thirty-one tons of coal. The glass may be considered as selling in average, duty included, for 1s. 3d. per pound, and the ton is hence worth £140. The coals at 6s. per ton, cost £9 6s., and hence the fuel makes up 6 2/3 per cent. of the value of the manufactured article. In Ireland, the cost of
p.227fuel being double in proportion, the cost should be 131/3 per cent. Now articles so liable to injury by carriage as earthen ware and glass are peculiarly adapted for local manufacture. The additional freight from England or Scotland here certainly counterbalances the advantage of 6 2/3 per cent. in fuel, the dearness of which cannot, therefore, be considered as negativing the introduction of those branches of industry, in which taste and artistic skill, are elements of cost as influential as the raw materials and rough labour.
A very laborious and truly useful inquiry has recently been instituted by Mr. Wilkinson, superintending architect of the Poor Law Commission, into the qualities of the various kinds of stone used for building purposes in Ireland. The results to which he arrived, were embodied in a memoir read to the Geological Society, to the economic museum of which institution he presented the collection of specimens upon which he had experimented, and which becomes thereby a standard of reference for the properties of almost every important quarry in the country, accessible to every individual. The stones which he submitted to trial were altogether 600 in number, and included all the known varieties of each kind of rock found in Ireland. They were examined under three different points of view. First. That of the tendency to absorb water, which determines principally the decomposing action of the atmosphere upon them. Second. As to their capability of resisting transverse fracture, which was essayed by loading a square piece of twelve inches by three, supported at each end, till it broke in the centre. Finally, their capability of resisting a crushing force, which was tried by pressing on an inch cube of the stone, by means of a lever, loaded until the stone gave way. It is to be hoped, that for the benefit of those engaged in building and practical architecture, the details of those experiments may be published. The general results, with a few examples of the extreme cases, can only be stated here.
The ordinary limestone of Ireland weighs in average per cubic foot 170lb. The extremes of weight were 159 and 180lb.
The average weight of water, which it absorbed by immersion, was one-fourth pound, the greatest absorption was one-half pound of water. The chalk of Antrim weighs 160lb per cubic foot, and absorbs three pounds of water. The impure shaley calp weighs 160lb, and absorbs from one to four pounds of water per cubic foot.
The average weight of sandstone is 145lb per cubic foot, the extremes are 123 and 170lb. The absorption varies from nothing to upwards of ten pounds, the average being five and a half pounds.
Granite averages per cubic foot 170lb. Its extreme weights were 143 and 176lb. The granite of Newry and of Kingstown absorbs one-fourth pound, that of Carlow from one and a half to two pounds, that of Glenties in Donegal four pounds.
Basalt weighs from 171 to 181lb per cubic foot, the average is 178lb. It absorbs less than one-fourth pound of water per cubic foot.
Clay roofing slate weighs from 174 to 179lb, in average 177, the absorption is less than one-fourth pound. The soft clay-slate from Bantry absorbs about two pounds.
In resisting fracture it was found, that the slate rocks were the strongest, and of these some are stronger when the pressure is applied on the edges of the cleavage planes than on the faces. The basalts are next in strength: then the limestones, then the granite, and the weakest are the sandstones.
Considered in relation to a crushing force, the basalts are found to be the strongest stones, next the limestones, and successively the slates and sandstones. In the different varieties of limestone, some of the largely crystalline stones and the compact hard calp are the strongest. The light coloured crystalline stones of Ardbraccan, and those around Cork are the weakest. The Connemara white marble or primary limestone, is the strongest that has been found. The strongest sandstones are the red rocks of the south, and the hard quartzose grits of the north of Ireland. Among the weakest are the county Down quarries, and the sandstones in Antrim, and around Clonmel, and some of the coarse quartzose sandstones of Donegal. From trials of the slates, Mr. Wilkinson found
p.229those of Valentia to resist pressure less effectively than those of Killaloe, and those of Mr. Synge's quarries in Wicklow, are about intermediate. From the experiments on granite, with regard to crushing force, no positive conclusion can be as yet drawn, but Mr. Wilkinson finds it not to possess any superiority over many of the stones in ordinary use.
It is observable in these experiments, that the denser stones are generally those which absorb least water, and which would, therefore, be best fitted for resisting the weathering influence of our climate; also that the power of resisting transverse fracture, and of resisting a crushing force, are by no means connected. A rock, as clay-slate, may rank high under one, and very low under the other point of view. Hence in different parts of a building, it may be proper for the architect to employ stones of diverse nature, and from the tables of numerical results, which Mr. Wilkinson has obtained, the magnitude of a pillar or transverse beam, to support a given weight, or bear up a transverse load, may be now for the first time calculated for the various building materials of our country. It would not suit the general object of this work, to enter into the detail of this subject, especially as all the particulars of these experiments will be published by Mr. Wilkinson in an independent form, and that by visiting the Economic Museum of the Geological Society, which is liberally thrown open to the public, the specimens themselves may be examined, and the documents regarding them referred to, with the assistance of Mr. Oldham, the able Curator of the Society's Museum.
The clay-slate rocks in various parts of Ireland have been quarried for slates for roofing purposes, and for flags, to a very considerable extent in several localities. In Wicklow, near Rathdrum, and at Glanmore, where Mr. Synge is now carrying on operations on a considerable scale, giving employment to upwards of 100 persons, and bringing into the market, slates of a quality and appearance fully equal to those imported from Bangor, with the slate of which, indeed, the district in which Mr. Synge's quarries are situated is geologically identical. I may remark, that it is found in all slate districts, that the more superficial strata are soft, and of a very inferior
p.230quality, and that to obtain first rate slates, it is necessary to sink to a considerable depth. It arose from this, that when various individuals first brought Irish slates into the market, their quality was very universally condemned, and a prejudice arose against their use, which is even yet not quite extinct. However, the workings in Wicklow and elsewhere have fully now brought into play strata of excellent nature, and this source of domestic industry, it is to be hoped, may be considered as well established.
The most extensive slate quarries in Ireland are near Killaloe. They were for many years worked by the Mining Company of Ireland, but when that Company removed its operations in order to concentrate on the productive copper mines of Waterford, the slate quarries passed into the hands of an English company, by which, under the name of the Imperial Slate Company, they have been since worked with considerable success. The slates are of the very finest quality, and can be had of almost any magnitude; there are some in the Museum of the Royal Dublin Society of ten square feet area. The stone is, for building purposes, one of the best in Ireland.
This district of slate rock is upwards of twenty square miles in extent, but the operations of the Company have been latterly confined to the two most important quarries, the Big Pit and Cunaghbally. These have been thoroughly drained, and the soft bad rock blown away, and in 1842 an acre of pure slate rock was laid bare in Cunaghbally quarry. In the Big Pit all the veins and strata proved to be continuations of Cunaghbally, and a vast extent of beautiful slate rocks from eight to ten feet in length have been exposed. These two quarries produce about 10,000 tons of manufactured slates per annum, and if a greater demand occurred, the Water and the Spout quarries could be put into immediate operation. By the operations of this Company, employment is given to more than 700 men and boys, and all who visit the district are equally struck with the unexpected size and magnificence of the quarries, as with the good order and appearance of the men, whose steady industry and comfortable mode of living, in a district which some years ago existed only as a desert mountain, may
p.231serve as an encouraging example to the starving and semi-barbarous agricultural population by whom they are surrounded.
The island of Valentia, consisting of the upper or silurian slate, is also a locality in which this rock is worked for industrial purposes. It cannot be split so delicately as to serve for the finer roofing slates, but its great strength, and evenness of texture, render it most useful as a building stone, and for flags, of which a very large quantity is annually sent to London. Slabs of Valentia slate are easily attainable thirty feet long, four or five feet wide, and from six to twelve inches thick, so that of it, without any intermediate bearing, the floors and ceilings of large rooms might be constructed. In the quarries of Valentia, about 200 individuals usually obtain employment.
The carboniferous slate of the south-east of Cork has been quarried in several places, and has yielded roofing slate of good quality, the produce having been found exceedingly light and durable. The principal quarries were at Clonakilty and the Old Head of Kinsale.
At Bradford in Clare near Killaloe, slate quarries had been opened many years ago, and are still worked to a certain extent. The clay-slate of Westport in Mayo was also worked some years ago, but its quality was not such as to stand the competition of slates imported from other sources.
The limestone districts of Ireland contain numerous beds, which the closeness of texture, and the purity or variety of colour, render available for ornamental purposes, as marble. I shall only enumerate the localities in which the most remarkable marbles are found. There is no county which does not afford specimens of greater or less excellence.
The principal quarries of black marble, are those at Kilkenny, and near the town of Galway. These are both in the upper limestone. The Kilkenny marble takes a beautiful polish, and, when first cut, is quite black, but the organic matter to which its colour appears to be due, gradually passes off, and ultimately white marks of fossils, of varied and interesting forms, present themselves upon its surface. The Galway marble
p.232quarries are situated along the verge of Lough Corrib, they supply a large quantity of marble annually to London and New York, but are capable of almost indefinite development.
Near Armagh is found a marble, which, from the excellence of its surface, and the variety of red, yellow, and brown tints which it shews, possesses great beauty. It contains abundant fossil remains of fishes. A similar marble, elegantly variegated with yellow and purple, occurs at Churchtown, in Cork, which county is indeed rich in this material, there being found
Black marble, at Churchtown and Donerail.
Purple and white, and blue and white marbles, also at Churchtown.
Ash-coloured, gray and dove-coloured marbles at Carrigaline, and Castlemary.
Pale brown marbles at Kilcrea.
In Kerry, there are black and white variegated marbles near Tralee; and in the islands in the River Kenmare, near Dunkerron, marbles of various colours, black and white, purple, white, and yellow, and some specimens of a purple colour, veined with dark green, resembling bloodstone.
At Craigleath, in Down, at Lyons and Ballysimon in Limerick, at Westport in Mayo, and at Castlebegs in Tipperary, are quarries of black marble. At Clondeslough in Clare, a fine bourdella marble. Near Shannon Harbour on the Galway side, fine sienna and dove marble. At Clonmacnoise, King's County, and Dromineer in Tipperary, are fine gray marbles, variously tinted and peculiarly sound and useful. At Killarney, occurs a very beautifully striped white and red marble; and a brownish red, mottled with gray of various shades, at Ballymahon, in Longford.
The primitive limestones of Connemara and Donegal, supply white marbles, which in Galway is often absolutly pure in tint, but in Donegal is more frequently of a greyish cast. The Galway white marble has been already noticed, page 228, as the strongest of limestones, when used for building.
The west of Galway and Mayo is also remarkable for the serpentine rocks, which afford the beautifully variegated green
p.233and white marbles, so deservedly esteemed. The most valuable quarries of this remarkable mineral are situated near Clifden, on the estate of Mr. Darcy. This marble is exported in considerable quantities.
The sandstone rocks, as well of the older as of the newer geological formations, have furnished not merely building stones and flags of good quality, of which the principal sources are in Carlow, and at Kilrush and Moneypoint, in Clare, but also grindstones and millstones, which latter, especially those of Cuilcagh Mountain at Lough Allen, and Drumdowney, in Kilkenny, were formerly much esteemed. Their manufacture has ceased, but certainly not owing to inferiority in the material.
The sulphate of barytes, a mineral, which, ground to fine powder, is extensively used as a pigment, either by itself or mixed with the more expensive white lead, occurs very abundantly in various parts of Ireland. In Ulster it is found in veins in different parts of the old red sandstone districts. The lead mines situated in the granitic ridge of Leinster have this mineral usually as the vein-stone of the ore, and it might be hence obtained in large quantity. In Wexford, several large veins of it present themselves on the sea shore, and in the vicinity of Youghal it is found similarly circumstanced. The earth barytes extracted from this mineral, by processes into the detail of which it would not be suitable to enter here, is employed extensively in the potteries of Staffordshire, where the sulphate is itself also used in some quantity. The composition of the sulphate of barytes is in 100 parts,
Sulphuric acid . . . 34.4 Barytes . . . 65.6
The earth magnesia, and its sulphate, popularly known as Epsom Salts, which are so extensively employed in medicine and the arts, are prepared from a mineral, of which there exists vast quantities in Ireland, the magnesian limestone or dolomite. This stone is distinguished from common limestone, by its drab or fawn colour, its greater density, and its dissolving
p.234but slowly, and with gentle effervescence, in dilute acids. It occurs as a substantive rock but in one locality, at Holywood, on the south side of Belfast Lough, where it forms stratum of about sixty feet in thickness. It has been raised there, and exported to Glasgow, to be used in the manufacture of Epsom Salts, although no use has been made of it at home. Veins and smaller deposits of dolomite occur in different parts of the limestone districts, particularly where that rock comes into contact with, or near to other formations. The composition of this rock is perfectly definite, it consists of an equivalent of carbonate of lime and an equivalent of carbonate of magnesia, and, when pure, contains in 100 parts,
But the beds or veins of dolomite are usually rendered impure by intermixed sandy or clayey materials, and the earthy carbonates are often associated with a certain quantity of carbonates of iron and manganese. It is seldom, therefore, that the produce in magnesia equals that given above, and the following analyses of specimens from various localities in Ireland, will show the usual composition:
|Oxides of Iron and Manganse||0.95||3.10||1.50||0.60|
These are by no means all the localities in which this mineral is found, but they are sufficient to mark its usual practical composition. It would be out of place to advert here to the modes of extracting the magnesia from it, for which reference must be made to works specially devoted to chemistry.
I have endeavoured in these chapters to present such an account of the metallic and other minerals of Ireland, as, without entering needlessly into mining or metallurgic details, should indicate the localities of those rocks, which by the analogy of other countries, we may expect to be rich in metallic ores, or other substances useful in industry. I have also endeavoured to represent as faithfully, as the materials available by an individual would admit, the actual condition of our mines, the amount of produce which they yield, and of the employment which they afford to the people.
It results from these inquiries, that by far the greater portion of this Island is constituted of mineral formations, analogous to those of the principal mining districts of England and of the Continent of Europe. That in almost every quarter valuable deposits of the more important metals, rocks, and minerals have been found, and the quantity of ores raised and sold is annually on the increase. In many cases, mines and quarries, formerly abandoned, are now being worked with advantage, owing to increase of economy and skill, and it should not be a source of discouragement for the future prospects of our mineral industry, that numerous unsuccessful trials are made, for it must be recollected, that by such trials only, can the really valuable mines be ultimately found, and that localities and enterprizes, of which we now appreciate the final success, shew us but the result of numerous and toilsome searches, under which the first adventurers were too frequently depressed.