Transactions of the Geological Society, 1st series, vol. 3/On the Salt Mines of Cardona

XIII. Some Observations on the Salt Mines of Cardona, made during a Tour in Spain, in the Summer of 1814.

Member of the geological society

[Read November 3d, 1815.]

These celebrated mines occupy the head of a small valley in the immediate vicinity of Cardona, a town in the province of Catalonia.

This valley extends about half a mile in length, from the river Cardonero to the mines, in a direction from east-south-east to west north-west. Its north-western side is bounded by a very steep and lofty ridge, the summit of which is crowned by the town and castle of Cardona. The opposite boundary is somewhat less elevated; but both sides are considerably higher than the upper surface of the fossil salt. On entering this valley, the attention is arrested by bold cliffs of a greyish white colour, which are soon discovered to consist of one vast mass of salt. The sides and bottom of the valley are composed of reddish brown clay, forming a thick bed, from which here and there large imbedded masses of rock salt project in the manner of more ordinary rocks; especially along the winding ascent which leads up to the town of Cardona. The summits of the ridges which bound the valley on each side, are formed of a yellowish grey sandstone of a coarse texture, and containing many scales of grey mica.

The great body of the salt forms a rugged precipice, which is reckoned between 400 and 500 feet in height at the upper extremity of the valley, and is covered by a thick bed of the clay above mentioned.

The precipitous form is partly owing to the manner in which the mine has been wrought for a series of ages. There is no excavation; but the salt has been procured by working down perpendicularly as in an open quarry. The lowest part of the present works has a solid floor of pure salt which is not above the level of the bottom of the valley where no salt is found; but the real depth of the bed of salt has never yet been ascertained. The upper surface of the salt is not level; but appears irregularly elevated, according to the general outline of the hill in which it occurs.

The salt has been usually represented as forming an entire mountain: but though it here appears supplying the place of common rock, yet from its being confined to this valley, and not attaining so high a level as the surrounding hills, it would seem more correct to consider it as a mass or bed of salt filling up a valley, than as constituting a mountain, which according to some authors[1] is a league in circumference. These dimensions could only be obtained by considering the neighbouring heights as formed of this mineral; a supposition not countenanced by my personal observation, nor by the best information which I could collect on the spot.

The surfaces of the salt precipice which have been long exposed to the weather are not smooth, but cut into innumerable shallow channels, running in a tortuous manner, and divided from each other by thin edges, often so sharp as to cut the hands like broken glass. The channelled surface is evidently produced by the action of the winter rains, which have given the whole a striking resemblance to the surface of a mass of ice, which had been partially thawed and again frozen.

The general colour of the exposed surface is greyish white, with here and there a tinge of pale reddish brown, from the colouring matter of the superincumbent bed of clay. Towards the extremities of the mass of salt, extremely thin layers of a pure and plastic clay are insinuated between layers of salt, so as to give it the waved delineations which often occur in some species of calcsinter. The general mass of salt is however of the greatest purity; and in order to be converted into snow white culinary salt requires no other process but grinding. The greyish hue of the external surface is owing to the rain penetrating a portion of the salt, and by diminishing its opacity, depriving it of the whiteness which the fresh fracture generally presents. At the period of my visit the surface of this immense mass was perfectly dry, and in some places, where water had most recently flowed, was covered with a snow white efflorescence. This circumstance, as well as the sharpness of the edges above mentioned, shew the little hygrometric water in the atmosphere of that country, and the general purity of the salt from earthy muriates.

The fracture of the salt is highly crystalline, and usually exhibits large granular distinct concretions, which give it sometimes the appearance of a breccia, or of containing imbedded crystals

A perennial brine spring flows at the foot of the great precipice, and affords a strong proof of the little effect of water on this very compact salt. The aperture through which the stream has issued for many years, is not wider externally than two feet, and suddenly contracts to a few inches; while the channel worn in a solid floor of salt, through which the stream has long flowed, is not a foot in depth. This is partly to be ascribed to the water being saturated with salt; but, during the rainy season, the stream is much augmented, and thus cannot be supposed so highly charged with saline matter. Notwithstanding this, neither the solvent nor mechanical effects of the spring seem to have much effect on the fossil salt of Cardona. The waters of this spring flow into the Cardonero, leaving in the valley a thick scaly crust of salt, resembling the ice formed around our brooks in similar situations. During the rainy season, it is asserted that the stream carries down such quantities of salt into the Cardonero as to kill the fish in that river. This assertion rests upon the authority of Bowles, an able naturalist; but he undoubtedly was led into error when he asserted, that the waters of the Cardonero at some leagues below the mines yield no trace of salt: from which he inferred, that salt may, by motion, be converted into earthy matter. At Manresa, which is about twenty miles below Cardona, I tested the water of the Cardonero by nitrate of silver, which indicated the presence of an unusually large portion of muriate of soda. The taste of the brine spring at Cardona is intensely saline; and the hand immersed in it, on being exposed to the air, is instantly covered with a film of salt. The salt rock near its source is most elegantly veined with delicate waved delineations of an ochre yellow colour.

The clay which covers the bed of salt at Cardona and forms the sides of the valley, exactly resembles the clay found in the salt district of Cheshire, having when dry some resemblance to shale but becoming plastic when moistened. It is remarkably pure, and free from intermixture except of salt, large masses of which are occasionally imbedded in it.

No fibrous salt was to be observed at Cardona; nor did I discover the slightest trace of gypsum in that neighbourhood; a remark which was also made by Bowles. On the soil near the town, a small quantity of a saline efflorescence was however observed, which had the taste of sulphate of soda; but the loss of the specimen I collected, has prevented a more accurate investigation of its properties.

The salt mine of Cardona is wrought like an open quarry with pickaxes and wedges, by which the mineral is raised in considerable tabular masses. The part at present wrought presents an extensive horizontal floor of pure rock salt; the level of which is a little lower than the foot of the great salt precipice. An enormous mass of the same mineral lies between this precipice and the present mine, the removal of which will, in time, render the appearance of this interesting spot still more magnificent; for then the vast front of the rock salt bed will at once strike the eye from the lowest part of the mine.

Like every other public work in Spain, the mines of Cardona are in a languid state from the effects of the late war which has desolated the peninsula. Only two labourers are at present employed in quarrying the salt, and in wheeling it to the receiving house. Over these, eight overseers are appointed, who do duty in rotation; and ten sentinels are continually stationed around the mine to defend it from the depredations of the peasantry. Several clerks are employed in an office built at the entrance to the mine, and the whole is under the direction of an Intendente or Inspector, who wears the uniform of an officer in the Spanish army; for the mine is the property of the crown, and is most rigidly guarded. Notwithstanding the rigour with which depredators are punished, the peasantry frequently attempt to deceive the vigilance of the guardians of the mine. When detected, the usual punishment for a peasant is, even on the first offence, two or three years labour among malefactors in some of the public works in the province. A soldier is however less severely punished when he commits a similar transgression; he is generally sentenced to a few days solitary confinement in a dungeon of the castle. On asking an overseer the reason of this disproportion in the punishment of different offenders, he replied, that the soldier's poverty was supposed to extenuate his crime, while the peasant of Catalonia enjoyed comparative wealth, and could afford to purchase salt for the consumption of his family.

Such is the boldness of the smugglers and the jealousy of the government, that it is dangerous to visit the mines without formal leave from the Intendente; as the sentinels have orders to fire on any one seen loitering about them.

The workmen here receive considerable wages, and are all free labourers; each man receives daily twelve reals vellon, which at the rate of exchange last year equals three shillings sterling: lads are paid at the rate of eight reals, or two shillings; and boys receive six reals, or one shilling and sixpence.[2] The hours for work are a from six in the morning to seven in the evening (in summer); with the intervals of half an hour, between 8 and 9 o'clock, A.M. for breakfast, and two hours, from twelve to two, for dinner, and its usual sequel in Spain, the siesta.

The produce of the mines is pulverized by grinding it in mills, on the exact construction of our common water mills. This operation reduces it into an excellent culinary salt of a snowy whiteness. In this state it is sold to the peasantry of the surrounding districts, at the rate of thirty reals vellon, or seven sh. six d. sterl. per fanega of five arrobas of Catalonia, which equal 116 pounds avoirdupois.

As there are no roads practicable for wheel carriages in this part of Catalonia, the salt is carried from Cardona on mules or asses; the only beasts of burden that could travel in safety the rugged defiles in which this district abounds. It seems a part of the perverse policy of the Spanish government to discourage the formation of proper roads, lest it should facilitate the operations of the smuggler.

It would not be difficult to connect Cardona, by means of a canal, with the ocean; and thus the valuable produce of its salt mines might increase the revenues of the crown, and the trade of Barcelona. The channels of the Cardonero and Lobregat always contain a large body of water, and might easily be rendered subservient to the purposes of inland navigation. Besides augmenting the value of the mines of Cardona, such a plan, by facilitating the intercourse with the interior of this fine province, would stimulate the exertions of a people who only require an equitable government to become highly industrious.

It yet remains that I offer a few remarks on the nature of the country around Cardona, as materials for its geology.

Its general appearance is mountainous. The mountains are abrupt, but generally wooded. The vallies are narrow, and, where the declivities will permit cultivation, they produce abundance of good grapes and some corn. In coming from Barcelona, the traveller leaves, at a small distance on the left, the majestic Montserrat; and gradually approaches a mountain chain proceding from its northern extremity, which declines as it stretches towards Manresa. This chain consists of similar materials to Montserrat; viz. of vast beds of farcilite, composed of rounded masses of quartz, with angular pieces of siliceous slate, and fragments of clay slate united by a basis containing calcareous earth. The fragments of this farcilite become smaller as we go northward, and at last bear t striking resemblance to coarse greywacké; to which formation I am inclined to assign the pudding stone of Montserrat, and the chain of which it forms a part.[3]

On descending the rugged mountains of pudding stone into the valley of the Lobregat, before coming to Manresa, we observe strata of a bluish grey rock with interposed layers of a softer material of the same colour, which crumbles into sandy clay by exposure to the weather. Those strata have some resemblance to sandstone-flag; but an attentive consideration convinced me that they ought to be considered. as stratified greywacké approaching to greywacké slate. Above these we again find the farcilite, which is the prevailing rock about Manresa. All the rocks hitherto mentioned effervesce slightly with acids; a circumstance which connects them in some measure with the extensive limestone country to the south-west of Montserrat; and they all shew a tendency to split vertically into columnar masses. Beyond Manresa the farcilite occurs till the traveller crosses the ford of the Cardonero, when it is succeeded by s limestone of a dirty iron brown colour, and dull, almost earthy, fracture. Beyond the village of Suria, a sandstone, which slightly effervesces with acids, makes its appearance. This rock constitutes the sides of the valley which contain the fossil salt.

The immediate vicinity of the salt mines shews no other rock than a yellowish grey sandstone much charged with scales of mica.

We find thus that the salt rock of Cardona is accompanied by clay and sandstone, like our Cheshire salt formation. Limestone also is found near it; but the usual concomitant gypsum appears to be wanting, as well as foetid limestone. The great compactness and purity of this salt merits examination.

Though the country around Cardona is mountainous and rugged, it is inferior in elevation to the districts between it and the Mediterranean; as well as to those which bound it on the north. Immediately behind Cardona the mountains begin to ascend with increasing boldness until they unite with the grand chain of the Pyrenees.

I relinquish to others the difficult task of giving a probable explanation of the formation of rock salt; contented if my observations on the mine of Cardona can add any thing to the mass of facts which should guide us in the obscure but captivating speculations of geology.

  1. Introduccion A la Historia Natural y à la Geografia Fisica de Espana, por Don Guillermo Bowles.—Madrid, 1775.—Dillon, who translates him. Laborde, Itineraire descriptif, &c.
  2. This may be considered as liberal wages where the accessories of life, with the exception of bread, are cheap; at Cardona, mutton and beef costs 1 real vell. per 12 oz. Bread of the best quality costs 1 real vell. per 12 oz, Wine of the country (a very good red sort) is retailed at 6 quartos per bottle, or about two pence sterling.
  3. It may not be improper here to remark, that the common descriptions of Montserrat, are in several respects erroneous. It is not an insulated mountain, as generally represented; but is the highest point of a considerable chain. Its insular appearance, as seen from the high road between Igualada and Martorel, has deceived those who have never examined its north-eastern side. The touchstone, mentioned by Bowles and others, as entering into the composition of its pudding stone, appears by its fracture to he only a dark coloured common siliceous slate.