[from Descriptions of the Western Isles, 1819]
METALLIFEROUS veins are found in different parts of this island. They vary much in importance in the several places where they occur ; and the smaller, which have been observed at different times, have, as might be expected, fallen into such oblivion, that it is scarcely possible to procure accurate information about their situations. A few of these are still remembered by the old miners who were formerly employed in the works that were carried on in the larger veins ; and among them two or three were pointed out to me in Port Erin. It is unnecessary to take further notice of them than merely to say that they contain the same substances as the larger veins, and that they lie in the same direction. This direction is, in all the veins, from north to south, or nearly so ; the variations among them . exceeding two points. They are all nearly erect, and contain the same substances disposed in a similar manner.
The three principal veins which have been wrought, are at Laxey, Brada head, and Foxdale : some workings have also been carried on at Ballacorkish, and at Glen sash [Glenchass], near Port la Marie. It is now some time since they were abandoned, nor is there at present any prospect of their renewal. The information with respect to them which is now to be procured from actual examination, is therefore very scanty ; the more so, that the remains of the workings at some of them, are scarcely in an accessible state. A description of the structure of the Laxey vein, will almost supersede the necessity of entering into details respecting the others.
This vein comes to light at a short distance from the town of Laxey, in a small and narrow glen which affords passage to a mountain stream. It has been wrought by a drift opened on the course of the vein itself with an air-shaft from the surface. Another opening upon its course lower down the stream, is now filled up with rubbish, and therefore inaccessible. The course of the vein is N. N. E. and it varies near its entrance, from two to six feet in breadth, dipping towards the east in an angle which appears to amount to five or six degrees. In the miners report it is stated at sixteen or eighteen. The vein lies in the ordinary clay slate already described, which in this place is generally of a smooth texture and silky lustre ; but varieties of the finer graywacké composition, and of the quartzose and granular kinds, are also found in the immediate vicinity mixed with it. Fragments of all these substances, of different sizes, united into a breccia by an imperfectly crystallized quartz, form the vein stone. In the cavities, the quartz is sometimes crystallized, and the same happens in the other veins, at Brada head and at Foxdale ; from the latter which very splendid specimens have been obtained. In all these places the quartz crystal presents the same forms, namely, that of a short prism terminated by a pyramid at each end, and consequently attached by its side, or else that of the pyramidal termination only.
The metallic substances, consisting of lead, zinc, copper, and iron, are irregularly dispersed and mixed with the vein stone. Both the lead and copper have been wrought. The lead is found in the form of ordinary galena, mixed with the steel grained variety, and has therefore, when the latter has appeared sufficiently abundant, been subjected to the process of cupellation. Carbonate of lead has been said to have occurred with it, but I saw no specimens of that substance : the galena is never crystallized.
The copper is in the form of the yellow sulphuret, and, like the lead, was always found massive. It does not appear to have been attended by any other ore ; the carbonate of copper now found among the workings being the result of the present action of the air and the rains.
The blende, which is the only ore of zinc, is brown, and is frequently crystallized ; but in so confused a manner as not to permit the modifications to be ascertained. It is in considerable abundance, and is attended by some insignificant lumps of compact calamine.
Iron appears only in the shape of calcareous ore, and is. either massive, or crystallized in its most common form, namely, a part of the primitive rhomb with curved surfaces. Its nature was unknown to the miners, and consequently no attempt was made to apply it to use. It is here, as in the other veins, abundant.
The vein at Brada head is supposed to have been formerly wrought by the Scandinavian possessors of this island. The more recent workings have been now abandoned for about twenty years.
This vein lies due north, and, after intersecting the high promontory in which it is found, grazes the cliffs of one still further to the north ; appearing also in the high land on the southern side of Port Erin. It has been wrought at till the former points, by driving directly on the body of the vein, but the principal working has been on the northern boundary of this small bay. The position of the vein is erect, and appears, like that at nearly vertical, as far as any judgment can be formed from above. Its breadth is irregular, and where I measured it, varies from six to nine feet.
The circumstances which attend the Brada vein, are in every respect so like those at Laxey, that : it would be superfluous to describe them : I need only add that the greatest proportion of copper was found near its southern end, and that of lead near its northern one. The quartz crystals are also here occasionally encrusted by a deposit of chalcedony.
The history of the mine at Foxdale appears so precisely similar to those already described, with the exception of the granite formerly mentioned, that it is equally superfluous to dwell on it. The direction, dip, and composition of this vein, were in every respect the same. The only circumstance in which it differed, namely, the presence of the granite, is now incapable of being examined, from the demolished state of the workings.
It is also unnecessary to notice the two other veins which were mentioned. Neither of them was very productive, and as far as the reports of the miners go, they bore a precise resemblance to the rest.
Having thus detailed the little information which I was able to procure, either from personal observation, or recorded history, relating to the mines of this island, it only remains to enumerate the independent mineral substances which are found in it, having already described those which are evidently of foreign origin, in the account of the alluvia of the country and of the shore.
Quartz, as it is the most conspicuous of these, so it is the most various in aspect. It is found scattered, often in very large blocks, over every part of the surface. Its origin is easily traced to the schist, in which it is also frequently seen, forming detached irregular nodules or veins, of greater or less extent and intricacy. It is most generally of a pure. white, with a lustre approaching to the oily ; sometimes, of a grey and dirty hue. Occasionally it is found of a dove colour, and all these specimens assume at times a certain degree of transparency. In the vicinity of Laxey I observed fragments of white quartz stained irregularly with black ; the black matter appearing to be uncrystallized tourmalin, since crystals of this mineral were found shooting from it through the quartz.
In several places chlorite was found imbedded in small cavities in the quartz, and, as is very common, entangled in its substance.
Talc also occurs in the quartz in several situations. It is generally found in small scales, or in a more continuous form, in the rifts of that substance. In the metallic vein of Laxey it may also be seen in larger concretions, Consisting of minute particles aggregated in pulverulent or scaly lumps, and of a pearly brilliancy.
Mica is occasionally found in the quartz in similar circumstances, being readily distinguishable from the talc by the well known characters of both. A less common variety of this mineral, of a bright gold colour amid of a highly metallic lustre, occurs also in the clay slate, a rock with which it is rarely associated in a form so conspicuous. It forms irregular lumps of no great size, imbedded in the schist, and consisting of distinct plates confusedly entangled together.
A few metallic substances, independent of those enumerated in the description of the mines, have been found in the island, but two of them have not been traced to their native places.
Wolfram is most conspicuous of these. This was found in detached pieces, connected with quartz, in the vicinity of Foxdale mine ; but the attempts which were made to trace it to its source in the hill, did not succeed. The specimens still preserved, are of considerable magnitude.
It is asserted that manganese has also been found, but I was unable to procure any specimens I have no reason however to doubt the truth of the assertion. Hepatic iron ore occurs in Laxey mine, at Spanish head, and in other places, in small quantities ; and being sometimes minutely crystallized, has been mistaken for garnets. Specimens of it were brought to me under this title.
Common clay ironstone is found sparingly among the beds of clay, in the neighbourhood of Castletown and elsewhere ; but it is not entitled to any further notice.
Bog iron ore is also to be observed on the surface of the alluvial soil in several places, but, like the former, it requires no further description.
I have already mentioned that a red argillaceous iron-stone is seen in the neighbourhood of the sandstone near Peel ; and I may add to this, that yellow ochre has been found in sufficient quantity in some of the mineral veins, to have become at one time a matter of export. It is further probable that this ochre was at times mixed with a considerable proportion of decomposed sulphate of copper, since it appears by the mining reports, that copper was obtained in the furnaces from a brown powder which wasfound in considerable abundance. The mines having long since ceased to be wrought, no specimens of this substance can now be procured so as to permit its true nature to be ascertained.
Such is the list of the detached or independent minerals appertaining to this island, which either fell under my own observation, or concerning which I could procure authentic evidence ; and with that list I shall now close this account of the geology of Man.
J. MOYES, GREVILLE STREET, LONDON.