Transactions of the Geological Society, 1st series, vol. 2/Mineralogical Account of the Isle of Man
By J. F. Berger, M.D, M.G.S.
That the name of the Isle of Man should be owing to its situation, does not appear at all improbable. Such is the conjecture of the learned Bishop Wilson in his short but valuable “History of the Isle of Man.”
The appellation of the island, says that respectable prelate, is probably derived from "the Saxon word Mang, among, as lying almost at an equal distance between the kingdoms of England, Scotland, Ireland and Wales.”
With the exception of the work just mentioned, we scarcely find in the tours that have since been published any information directly bearing on the mineralogy and physical structure of this island till we come to the late publication of Mr. Geo. Woods, where indeed these topics are more fully detailed than is usually the case in general topographical descriptions.
In enlarging upon the same subject, I hope that I shall not occupy in vain the time and attention of the Geological Society; for a minute investigation both of the rocks and simple minerals had never been yet instituted, and the arrangement and examination of the high land, the most conspicuous and extensive part of the isle, till remained a field quite unexplored.
The grotesque and unfaithful attempt of Fannin to lay down the mountains in his map of the island published in 1789, can hardly be considered as an improvement upon the much earlier and rough sketches of Collins, Durham and Speed.
From the materials and documents which I collected when in the Isle of Man, I have since my return from Ireland constructed a map chiefly expressive of the features and appearances of the mountainous tract, which I now present to the Society; acknowledging at the same time the able and kind assistance afforded me by Mr. Webster, draughtsman to the Society.
The height of Snei-feldt was a long time ago determined by means of the barometer, by Bishop Wilson, and it has been since along with that of North Bor-roilva, in the trigonometrical survey of England by Lieut. Col. Mudge. But with these exceptions, no other elevations in the island were ascertained. A barometical measurement which I have made of nearly all the mountains and other remarkable places, has amongst other advantages, enabled me to give a vertical section of the chain throughout its whole extent, which agrees very well with a profile view of the island, taken by Murdoch McKenzie from the Mull of Galloway. The spelling of the Manx names along with their pronunciation and signification has been furnished me by several persons in the isle, well versed in the knowledge of their native language, but I am particularly indebted for it to the Revds. H. Stowell, To Howard, and Wm. Fitz-Simmons.
The length of the island is computed at upwards of thirty English miles, of which about five-sixths are occupied by a large body of mountains stretching from North-East to South-West; its breadth varies from fifteen to eight miles.
The chain spreads or swells out to the northward contracting itself to the southward into the Calf or Barrow of Man, which latter is rather less than six hundred acres in superficial extent, offering thus a gradual slope of fifteen hundred and forty feet from the top of Snei-feldt down to Burchet's house on the southern cliff of the Calf, that is to say, a depression of nearly a quarter of a mile in twenty-one miles taken in a straight direction, or, on a mean average, of about seventy-three feet per mile.
Estimating the mean breadth of the mountainous belt at four miles and a half, and its length at twenty-five, we should have for its superficial extent one hundred and twelve square miles and a half, which when referred to the whole area of the island, on the supposition of its being on a mean average, eleven miles and three quarters broad, by thirty miles long, or three hundred and fifty-two square miles and a half, would give one third, by approximation, for the ratio of the moory and uncultivated land to the land that is under tillage; there can be no doubt however, but a considerable proportion of the former is susceptible of being reclaimed.
Parallel to each other, but at a distance respectively different, and nearly vertical to the main direction of the chain, there are three transverse vallies, the bottom of which, if not on a dead level with the sea, comes at least very near to it. The first of these is situated in the middle part of the chain, and the road leading from Douglass to Peel town passes through it. Its watershed is one hundred and twenty-six feet above the level of the sea, from which on the northern side rises a steep slope of 1352 feet to the top of the North-Greebah, and on the southern side a nearly vertical precipice of 609 feet to the top of the North Slieau-Aalyn above the hamlet of Mullin-y-Chlea, which stands 93 feet only above the sea.
The second transverse valley is about ten miles in a direct line to the south of the first, between Purl-Keill-Moirrey and Port Erin. Its watershed is 81 feet above the level of the sea, and is a low ridge of land, formed by the gradual slope of Slieau-y-Carnane and the high land of Spanish head.
Two miles farther to the south, the narrow channel of the Calf, about two furlongs in breadth, forms the last transverse valley. The small Isle of Kitterland lies in the middle of the Strait, connected by shelving rocks discernable only at low water, both with the main of the Isle of Man, and with the Calf itself.
It is a remarkable fact that the trifling elevation of these three sections decreases southwards, down to the last which is below the level of the sea.
A fourth flat, more considerable indeed than any already spoken of, may be said to exist on the outskirt of the chain northwards, occupying that fenny plain anciently called “The Curragh,” and now transformed into one of the most fertile tracts of the whole island.
The chain of mountains that forms the middle part of the Isle of Man, considered in itself, might perhaps with more propriety be denominated a group than a chain. It is a rising “en masse” of the land, a common broad basis or foundation on which rest several mountains otherwise unconnected with each other, though disposed in some regular order.
The narrow Glen of Mullin-y-Chlea, may serve to distinguish the mountainous group into two divisions, the one north, the other south. In the northern district of the group, two extensive lines of mountains and a central one, may be traced without difficulty. The latter having Snei-feldt almost in the centre, comprehends the highest ground and the mountains of North Bor-roilva, Gob-y-Scioot, little and big Snei-feldt, Bein-y-phot, Kanaghyn and North-Greebah.
A boggy and elevated table-land lies on both sides of the central line of mountains, separating it from the two exterior ones. The summits of the extensive mountains do not all of them greatly surpass the elevation of the intervening table-land itself.
In the southern district of the group, the two exterior and skirting lines of mountains do not exist, but the eastern side of the mountains is rather scooped out and smoothed into a gentle and gradual declivity; whereas the western side constitutes a range of cliffs abrupt in most of its extent.
The steepness of the exterior mountains is nearly the same on each side. The northern boundary of the group terminates almost abruptly, and beyond the Curragh, lie the Balla-chyrrim hills, a low range formed of loose sand and gravel, facing the northern escarpment of the group, and then passing southwards in a parallel direction between the coast and the western exterior line of mountains.
A little to the north of the Balla-chyrrim hills, is a shingly beach, insensibly declining towards the sea, and formed of water-worn pebbles and sea-sand. The latter is hardened and binds the pebbles strongly together. It is the opinion of several persons in the isle, that the land in this quarter is gaining sensibly upon the sea. Some go so far as to say that the increase is not less than two yards in a year.
There are but few water-courses of any magnitude and extent in the Isle of Man. Sulby River the largest of all, irrigates the Curragh, and from the village of Sulby to Ramsey where it empties itself into the sea has but a very inconsiderable fall. From Crammag-bridge down to Sulby the stream runs at the rate of 452 feet within three miles; from thence higher up near to its source no computation of the kind can be made, as it is no longer one regular body of water but an assemblage of many little rivulets flowing down from the slopes of the mountains in every direction, particularly from the mountainous pasturage called Mount-Pellier.
The watershed of the elevated and boggy table-land that separates Mullach-Oure from the central line of mountains, gives rise to two other water courses, which from their common origin run in a contrary direction. The Bright-river after it has watered the Baldwin-valley empties itself into the sea at Douglass. The Laxey river flows through the valley of that name. Allowance being made for the windings of the Bright-river, it falls at the rate of 1395 feet within six miles, a fall rather considerable.
Both the Black-water and the Peel-river that issue from the watershed between Douglass and Peel-town are inconsiderable streams.
From the southern group of mountains come out two or three rivers, Glen-Moy, Cass-ny-Hawin and Castle-town rivers; the two latter flowing into the eastern part of the Irish Channel, and the first into the western.
The vale that is irrigated by the Moy river (Muigh a Druid) is extremely picturesque, the windings, which are short and frequent, expose unexpectedly to the traveller's eye, scattered cottages along the sides of the river. Cass-ny-Hawin and Castle-town rivers have a course much more open, owing to the character of the country which they traverse. Several other streams indent the coast of the island, which from the shortness of their course and the diminutive quantity of water they discharge into the sea, do not seem entitled to any farther notice. I shall speak first of the Compound Rocks, and secondly of some Simple Minerals, as they occur loose or in situ, mentioning besides in each division under a particular head the primitive rocks, and those that belong either to the class of Transition, or to that of the Flœtz-Rocks.
(a) Primitive Rocks.
Very little of the oldest member of the primitive class of Rocks is to be seen in the Isle of Man in Situ, nor is it the genuine old granite. Some doubts therefore may be entertained whether in the places where it occurs it does not lie in beds, rather than forming the universal foundation of the Isle.
Along the slope of Dun How, on the road from Laxey to Ramsay, and in the middle feeder of a stream that runs into the sea, occurs a small grained granite much decomposed, the quartz bearing but a very small proportion to that of the felspar: when breathed upon, the rock emits a strong argillaceous smell.
The same small granite, but in a sound state, is to be seen at Dun-bridge.
The spot where it comes to the surface may be three or four hundred feet above the level of the sea, but I have made no observation that enables me to determine accurately.
Another small grained granite was found in the working of a lead mine at Foxdale, a place situated nearly in the middle of the island, and 346 feet high.
If the information I received from an old English miner who had been employed the whole time the works were carried on be correct, they came to the primitive rock in sinking a shaft forty yards deep. There the granite was found to form the north side of the vein, the galena adhering to it, while the south side was a stratified rock, which I shall hereafter mention. Whatever may be the depth at which the primitive rock was first remarked, there can be no doubt as to its existence, from the multiplicity of pieces of all sizes I found among the rubbish of the mine, and which were pointed out to me as such by the miner himself.
The rock is of a coarse grained texture, somewhat loosened, chiefly composed of quartz concretions, with reddish and decayed felspar along with some plates of white mica.
The mean specific gravity of the different sorts of granite above mentioned, is 2,81. From the granite above described, we come at once to the clay slate formation. The subsequent or intermediate members to granite in the series of the primitive rocks, viz. gneiss and mica slate, being either wanting absolutely, or if they exist at all, having escaped my attention, or being for the present concealed from our sight.
The clay slate formation in the Isle of Man does not appear to belong to the oldest kind of Werner. It is almost limited to the high ground occupying Snei-feldt, Bein-y-phot, South Borroilva, and Cronk-ne-liry-Lhaa. It also occurs at Mount Pellier as hone stone; at Peel-hill and Balla-Gawn, as roofing slate; and as a reddish half-decomposed slate along the mountainous road that runs from Ramsay to Douglass, between Slieau-Lhearn and little Snei-feldt.
The clay-slate of Snei-feldt has a close texture. Its basis is remarkably fine, the gloss not very resplendent: it fuses into a brownish enamel, and is traversed by slender veins of granular and whitish quartz.
The clay slate of Bein-y-phot has a dull black-brown colour, while that of Cronk-ne-liry-Lhaa is sometimes so glossy as to resemble plumbago, is soapy to the feel, fusible into a yellowish and bubbly enamel, the fracture is foliated, with some minute specks of white mica.
On the slope of South Bor-roilva the clay slate assumes a more flinty character, the grain is also very close. At Peel-hill, in a situation still lower than on the slope of South Bor-roilva, we come to another flinty clay slate, in the basis of which are distributed extremely minute specks of mica; it fuses into an olive brown enamel. The rock is quarried, but the beds that are used for roofing alternate with two others of a different nature. The one is a greyish compact felspar, the structure of which is rather thick slaty, with a close texture, the fracture is short scaly, it contains dispersed specks of mica, and fuses into a white frothy enamel. The strata run nearly East and West, dipping at an angle from 75° to 90°. The other bed alternating with the roof slate is called the Knobby Side, and forms the wall of the quarry itself. It has a silky lustre, and the planes of the strata, which are nearly vertical, instead of being even, offer little cavities smoothened and adapted for the reception of prominent parts similar in dimensions that exist on the contiguous bed. There is another roof slate at Balla-Gawn of a dark grey colour, rising by flags and of a fissile texture.
The clay slate of Mount Pellier has a structure rather thin slaty, it is ferruginous on the joints, but the colour of the basis is greenish grey, of a very fine grain, and full of cubic iron pyrites. It is a fact worth noticing, that the parts of the rock contiguous to the pyrites are whitish and earthy.
The last sort of clay slate mentioned as occurring between Slieau-y-Carnane and little Snei-feldt, has a violet reddish tinge. The structure is fine slaty, the texture more clayey; talcose linings impart to the spontaneous joints a glossy character. Its readier decomposition makes it a better support for vegetation. The mean specific gravity of the different sorts of clay slate enumerated here, is 2,757.
We pass from the clay slate formation to transition rocks through the most insensible gradations, and in this instance it is to be remarked, that it is the grey-wacke and not the limestone which forms the oldest member of the series.
In the Isle of Man this rock, as far as my observation has gone, never contains organic remains. It is farther to be observed that the tract of land occupied by the grey-wacke is less elevated generally speaking, than that appertaining to the clay slate. We can trace the grey-wacke all along the contour of the island, and, except those places where it slopes down gradually, and is outskirted by the flœtz-limestone receding into the sea, it forms a range of bold cliffs; at Maughold-head, Banks-how, Douglas'-head, Walberry-how, Spanish-head, the Calf of Man, Brada-head, Dauby-point, and in the intervening space between Peel-town and Kirk-michael.
Cronk-dhoo is the highest place where I have observed the grey-wacke. The shade indeed that seems to discriminate it from the clay-slate is so delicate, that were I to speak decidedly it would be rather unphilosophical. It has a grey colour inclining to a greenish hue, the joints ferruginous; it possesses a silky lustre which it seems to derive from talc intimately blended or interwoven with the basis itself, but there are besides a good many small specks of mica.
At Banks-how the grey-wacke has a much more decided character. It is rather thick slaty and of a granular texture, traversed by veins of white quartz standing out in relief. The basis has a greenish tinge approaching to grey, contains no spangles of mica and comes near to quartz sandstone. When disintegrated it forms but a meagre soil, fit for little else than oats.
Large tabular masses distinguish the grey-wacke of Clay-head. The fracture in the small is granular-scaly, the colour greenish grey, passing to ferruginous on the natural joints, it does not fuse unless where there are spangles of mica.
Near Laxey there is a grey-wacke-slate used as flags for flooring houses, it is scarcely fusible but for the mica there is in it, thin coatings of an ash-grey colour over-run the surface.
The following beds of grey-wacke-slate, alternating with each other, appear on the south quay of Douglass.
First variety. Texture earthy, of a dirty grey colour, contains spangles of mica, fuses into a whitish enamel.
Second variety. Striated, of an hard and dry aspect, infusible, or merely glazed from the mica that enters sparingly into its composition. The colour varies from greyish to olive-grey.
Third variety. Granular quartz forms the basis of it, in which are interspersed some small grains or nodules of transparent quartz, and some specks of white mica.
The Fourth and last variety, is a granular quartz over-run by veins of the same substance. There are in it but a few specks of mica.
The grey-wacke of St. Ann's-head is distinctly stratified, the planes of the strata being quite even, a mode of structure which originates from an accumulation of specks of mica, which render the rock readily fusible into a brown-greyish enamel, while it is infusible in those parts where the mica is wanting.
Along the shore between Kirk-michael and Peel-town, the grey-wacke is rather thick-slaty, traversed by slender and parallel veins of white quartz, coeval with the rock itself since they occur along the seams of stratification. The mean specific gravity of seven specimens of grey-wacke is 2.702.
C. Flœtz Rocks.
It would seem as if the appearance of the limestone was connected with the absence of the exterior line of mountains on the eastern side of the South Group. We trace it from Cass-ny-Hawin River to Purl-Keill-Moirrey (Langness-point excepted) but it never reaches to any elevation on the slope of the mountains; it is confined to the shore or its vicinity.
It lies conformably over the most superficial of the produced strata of grey-wacke, but the dip becomes less as the strata retreat farther back from the land into the sea. It may be comprehended between 10° and 20°.
This secondary limestone is accompanied by the magnesian limestone, but I cannot say that the one overlies the other. They rather seem to occur by separate beds, or sometimes by patches, the one within the other. The magnesian limestone does not put on that regular stratified appearance which is so conspicuous in the other, nor have I observed in it any organic remains but in one single instance, and they are similar in their composition to the stone itself
Mr. Parkinson has most obligingly furnished me with a list of the organic remains contained in the limestone of the Isle of Man, and he farther remarks, that the whole much resemble those found in Westmoreland, Cumberland, Durham, and, as far as he can judge, those of Kilkenny in Ireland.
The following are the organic bodies contained in the specimens that were submitted to his examination.
A large madrepore from two to three inches in diameter with distinct branches, a small madrepore with distinct branches, minute madrepores and entrochitæ, large trochitæ and terebratulæ, the latter varying from two inches to half an inch in diameter, large entrochi, small fragments of minute trochitæ.
The limestone of Castle-town, Scarlet, Pool-vash, and Ball-Fhallack is of a grey, or more generally of a dark grey colour: the texture compact with some lamellar concretions. It is traversed by slender veins of calcareous spar, and the dip-joints are coated with crystallized calc spar. As the texture becomes more compact it gets harder and of a more intense colour, approaching to black; the fracture at the same time approaching to conchoidal. Iron pyrites dispersed through the mass is not uncommon, and when scratched the smell of sulphuretted hydrogen is rendered sensible: it burns very white, a circumstance which shows that the colouring matter, being volatile, is of an animal or vegetable origin. In diluted muriatic acid it makes a rapid and brisk effervescence, leaving rather a considerable residuum. The mean specific gravity, as resulting from eight specimens, I found 2,704.
I am not aware that the dark marble-limestone of Pool-vash contains organic remains; I have seen stripes or veins of lamellar and greyish limestone full of petrifactions alternating with the darker variety that remained quite freed from those exuviæ.
Thin and crumbling strata intervene between the solid strata of limestone. They are called Soles in the Isle of Man, but generally Partings among the miners.
The magnesia limestone in the places where it occurs, differs enough in itself to induce me to give a particular description of it. At Cass-ny-Hawin it is either finely granular or in lamellar and well determined crystals. In the latter case it abounds with small cavities filled with crystallized rhomb spar, the crystals of which turn quite brown before the blowpipe, The texture of the lamellar variety is not so close as that of the other. The specific variety of the latter is 2.777, and that of the first 2.820.
The magnesia limestone that appears along Castle-town river from Ball-Fhallack towards Athol-bridge, is remarkable for a circumstance that has not as far as I can remember been yet noticed. I mean the occurrence of quartz-nodules, sometimes above the size of a pea and even of a bean. The quartz is quite glassy, and the concretions perfectly distinct, as if they had been water-worn and subsequently imbedded in the limestone itself. This is not however a conclusion I should adopt, as it seems to me that their existence may be better accounted for by way of crystallization. The colour of this magnesia limestone varies from bluish-grey to dirty-yellow; it makes a very slow effervescence with diluted muriatic acid, contains rhomb spar either in lumps or on the seams of stratification, and sometimes sparry iron ore; the latter before the blowpipe assumes the character of a slag, which acts sensibly on the magnet, whereas the bitterspath, though it turns brown, is not attractable. The powder of the sparry iron ore of a brown colour effervesces briskly with diluted muriatic acid. The specific gravity from three specimens is 2.81.
At Scarlet point the magnesia limestone has a yellowish-grey colour, and is close in its texture. Patches of compact greyish lime-stone are imbedded in it.
A dyke occurs in the limestone formation at Scarlet point, upon which I shall say no more for the present, as it is a subject which I intend at some future period to bring before the attention of the Society.In the little bay of Purl-Keill-Moirrey, the limestone on account of its low retreating strata, imitates a sort of causeway, ending towards the high land of Spanish head.
Kaal-Farane and Cromwell' walk, two places that separate Scarlet point from the entrance of Pool-vash bay, present an unstratified bed of amygdaloid that overlies the limestone itself.
The basis of the amygdaloid is a wacke of an earthy texture, dull and of a greenish-grey colour, emitting a strong argillaceous smell when breathed upon. There are in the powder a few particles that effervesce with acids; the rock however fuses readily into a dark olive bead that is attracted by the magnet. There are in the basis nodules of lamellar calcareous spar, lined on their periphery with iron pyrites: the cavities they are imbedded in are smooth. When by the action of external agents the more tender nodules have been washed away, the rock partakes of the appearance of a slag, inasmuch as the basis is itself of a dirty red brown colour. The mean specific gravity from three specimens is 2.592.
It occurs both under the form of fine granular and of conglomerate, of a red and grey-white colour, a little to the north of Peel town on the shore, and also on Langness isthmus. In the first place the strata run south-west and north-east, dipping north-west at 39°. At Langness, as we approach towards the south point of the isthmus, the conglomerate strata get higher and more thick-slaty. The materials entering into its composition are of a large size and much loosened. Along the Castle-town River, the sandstone overlies the limestone.
II. Compound Rocks not in Situ.
(a) Primitive Rocks.
I am aware but of two modes of explaining the existence of loose blocks of rocks that are spread over the face of a country, whatever may be the nature of the blocks themselves, either to suppose they are extraneous to the places where they now lie, or that, howsoever unconnected they may appear to be with the materials that surround them, they are nevertheless in their birth-place, and have been disintegrated in situ, covering and resting upon solid and continuous strata similar to themselves.
The only criterion perhaps applicable to the determination of this important question is the following. When by farther investigations we have found that the hidden and continuous rocks are similar to the blocks themselves, we may safely venture to say that the latter are indigenous.
I am inclined to think that several of the loose blocks I am going to describe; whenever they occur in any number, are in their birth-places.
On the beach towards Aire-point there are innumerable loose blocks of granite, one of which, rather large in its dimensions, I observed on Aire head at the elevation of 271 feet. They all in theircharacters differ but little the one from the other. The rock is a small-grained granite, composed of white felspar, quartz and black mica, with a few incidental plates of the latter that are white. In one of the specimens I collected, there is a rectangular piece one inch in length by half an inch broad, of very minutely grained granite with a predominance of mica.
On the slope both of South Bor-roilva and Cronk-ne-liry-Lhaa, in the southern part of the group of mountains, occur abundant blocks of rather decayed granite, composed of yellowish and white felspar turning to a state of earth, and disseminated plates of white mica. The texture is loosened to such a degree that large fragments often yield under the pressure of the hand.
I traced blocks of the same granite in Glen-Moy, though the bed of the stream is hollowed out in the grey-wacke formation.
The central stone of a Druidical barrow in Kirk Ballaugh, is a small grained granite of white felspar, quartz, mica, and a great deal of hornblende.
A vast number of blocks of mica-slate exist on the slope of Slieau-y-Carnane, another hill in the southern district of the group. The quartz is finely granular, and has a silky lustre, which it probably derives from a superficial covering of talc. The plates of mica are white and sparingly dispersed, sometimes crystallized.
I met at the village of Craig-neash with a large settled block of mica-slate. The quartz is of a dirty-grey colour. The plates of mica very few and falling into decay.
Very numerous blocks of this rock occur on the beach at Aire-point. The basis is compact felspar of a flesh-red colour, turning yellowish and earthy when going to decay. There is some hornblende disseminated throughout the mass: a few crystals of lamellar and transparent felspar are also imbedded in the basis. The rock acts strongly on the magnet. It emits when breathed upon a sensible argillaceous smell.
I noticed but one block forming part of the Druidical barrow already spoken of. The texture is unusually close. The two ingredients are crystallized and intimately blended together. The felspar fuses, but not readily, into a transparent enamel which is not frothy. There are besides in the mass some very minute crystals, of an yellowish colour with a vitreous lustre. (Qu. garnets?) Specific gravity 2.932.
Several blocks of white and greasy quartz, some of which contain yellowish talc, form one of the circles of the Druidical barrow in Kirk Ballaugh. Sp. gr. 2.536.
†††††† Garnet Rock.
This rock, of an unusual occurrence I believe, I found under the form of water-worn pebbles on the shore at Kirk-michael, and as this is no place for vessels to lie at anchor, I have no reason to think they could have been taken as ballast and thrown away where I remarked them. The rock is highly magnetic, very hard and tough. The mean specific gravity 2.967, the extremes being 3.085 and 2.846. The mass is of a liver-brown colour, with many crystals of an orange or reddish-brown cast imbedded in it. Their fracture is vitreous, but sometimes displays a sort of lamellar texture. The crystallized garnets are much less fusible than the basis or massive garnet: the latter passes into a brownish bead. There are besides in one of the specimens some nodules of radiated zeolite or mesotype. In another the mass of garnet is blended with white felspar.
At B. Wodden I noticed a large block of granular quartz with garnets? and hornblende. The rock has a greenish-grey colour. The fracture in the small is granular scaly. Another rock, related to the preceding, is amongst the Druidical stones of Kirk Ballaugh.
(b). Transition-rocks not in Situ.
Between Ramsay and Aire-Point I saw in some heaps of stones a number of pieces and blocks of greywacke, passing from large grained into a small grained texture. The basis is greyish, the imbedded fragments are mostly nodules of white quartz with scraps of a dull and black sort of slate, fusible into a whitish enamel, and abraded plates or broad spangles of mica. The cavities that receive the nodules of quartz when freed from them, appear smooth and even. The pieces of slate turn sometimes clayey, micaceous, and of a brown ferruginous colour.
I shall merely speak here of some water-worn limestone pebbles found in great plenty from Kirk-michael to Jurby point, though no solid strata of this kind can be seen in situ. They are picked up and burnt for lime, which I was informed is preferred by the northern farmers to the Castletown lime for manuring the land. The colour of these pebbles is smoke-grey, the texture granular with lamellar crystals; they are soluble with a brisk effervescence in acids, leaving behind only an inconsiderable residuum. They contain organic remains.
III. Simple Minerals in Situ.
† Lead Glance or Galena.
Lead glance or galena is the most conspicuous of all the simple minerals I have to mention here. It forms three limited repositories, one at Laxey, the other at Foxdale, and the other at Brada head.
No workings are carried on at present.
As to the precise time those mines were first opened there is, I think, some uncertainty. It would appear from the following passage taken from Bishop Wilson's History of the Isle of Man, that there had been mines wrought at an early period; “ Mines of coal there are none, though several attempts have been made to find them. But of lead, copper, and iron, there are several, and some of them have been wrought to good advantage, particularly the lead; of which many hundred tons have of late been smelted, and exported. As for the copper and iron-ores, they are certainly better than at present they are thought to be; having been often tried and approved of by men skilled in those matters. However, through the ignorance of the undertakers or by the unfaithfulness of the workmen, or some other cause, no great matter has as yet been made of them.”
These three repositories of lead lie in a grey-wacke formation, with the exception before mentioned, when speaking of a small grained granite found in the sinking of a shaft at Foxdale.
From the direction of the metallic veins, they seem to intersect at a greater or lesser angle the greywacke-strata. The direction of the metallic vein at Laxey is West South West, and East North East; at Brada head, the shafts have been opened in a line that keeps nearly the same direction.The inclination of the metallic vein with respect to the horizon, both at Laxey and Foxdale, is two yards in six.
The breadth of the main metallic vein at Foxdale, the partings being included, was computed to be full six yards.
In all the three places the vein appears adherent to the contiguous rock, whether it be greywacke or small grained granite.
At Foxdale a cross metallic vein of lead also was found running a few points from the North and South, that is to say, intersecting the main vein at a great angle; at the junction or counter, the ore grew richer, and many knockings, shods, or balls occurred. The cross course was as fertile as the main vein itself, if the information I received be correct. Its inclination likewise, with respect to the horizon, was fully as considerable.
According to Mr. Wood's statement, it would appear that the ore at Brada-head was chiefly sulphuret of copper.
I shall now enter into a more minute examination of the several substances which accompany the lead-ore at those three places.
The galena of Laxey, when pure, is possessed of the lustre characteristic of common lead-ore. Its specific gravity is 7.652.
Sex octagonal carbonat of lead, along with efflorescent and fibrous carbonat of copper, are the various minerals attending the lead-ore. A button of copper may be easily obtained by exposing the carbonat of copper with borax to the heat of the blowpipe.
The vein-stone or Rider, is a greywacke breccia, composed of pieces of silky-greywacke, quartz, and bitters path, with much brown blende. The walls of the vein are formed of silky greywacke with pieces of bitterspath, and a few flesh-red and lamellar crystals of calc spar.
The specific gravity of a rather impure specimen of lead-ore, I found 6.095.
Amongst the stony substances that fill up the vein, I remarked the following varieties:
A semitransparent and bluish chalcedony passing to white; it is zoned, but the zones are not apparent without the assistance of a magnifying glass; common galena and some iron pyrites are disseminated throughout the mass.
Sometimes the chalcedony verges into white quartz, blended with sparry iron-ore scarcely effervescent with nitric acid, turning almost black before the blowpipe and acting very powerfully on the magnet. It is likewise accompanied by iron-pyrites.
The sparry iron-ore in larger lamellar crystals appears of a dark colour, and contains so much of iron as to act by itself on the magnet. Galena adheres to it.
The greywacke that forms the South side or cheek of the vein, is of a greyish colour with a silky lustre; the common lead-ore adheres to it. In a granular and drusy quartz filling up the vein, I noticed a few garnets.
The specific gravity of a less impure specimen of lead-ore than that of Foxdale, was 6,622.The principal vein-stone through which the ore is disseminated, is a yellowish granular quartz that includes iron pyrites.
On the part of Dun How where the granite appears at the surface, and in a natural excavation, but which I believe has been enlarged by art, there is a brown sort of powder, said to be used by the inhabitants for the cleaning of plate. It feels rather soft to the touch; does not effervesce with acids; fuses per se, but not readily, into a greyish enamel.
All over the curragh, and on the beach also at Kirk-michael, a substratum of marl several feet deep, underlies a light and sandy soil.
Calcareous marl of a light flesh colour, soft enough to be cut with a spade, feels almost greasy to the touch, basis extremely fine, texture dull and earthy; no other discernible particles in the mass but very small spangles of white mica; adheres to the tongue strongly, is soluble with a brisk effervescence in diluted muriatic acid, leaving a considerable residue readily fusible into a slightly magnetic olive enamel.
Calcareous marl of a grey-reddish colour, not so soft as the preceding, owing to some sandy particles immersed in the basis; leaves in diluted muriatic acid a more abundant residue, not so easily fusible; the enamel of an olive-green colour.There is another variety of calcareous marl in the same place of an ash-grey or of a dun colour.
One hundred and fifty tons of marl are computed to be necessary for an acre of land. The expenses, supposing the carriage not to exceed a mile, will amount to six pounds sterling. The cost of liming, a practice chiefly used in the southern part of the isle, is nearly the same. Ninety bushels of lime is the quantity allowed for covering an acre of lands. Sea weeds previously made into a compost, are also much used in the south district of the island. The marl by lying at the surface sometimes becomes considerably lighten When dung mixed with hot lime is put upon a marled ground, the fermentation that ensues produces a very surprizing effect.
It is unfortunately more as a warning against the delusive accounts that have circulated abroad with respect to the discovery of coals in the Isle of Man, that the present topic is introduced here, than to prove their real existence. To preclude however, farther investigations and observations on the score that coals cannot possibly be discovered, would be presumptuous and imprudent, but nobody has yet, that I am aware of, substantiated their existence, The only serious attempt I believe to find coals in the isle, was made at Derby-haven, many years ago by a speculator from Cumberland. After having gone to a certain depth, not finding traces of them, he gave up the search as fruitless.
While I was in the isle (June 1811), two or three spots in the north-western part, were particularly pointed out to me as places where coals did actually appear, or were cropping out. But when the matter was strictly enquired, the reports turned out unfounded. While on the subject of coals, I shall beg leave to present here an account of the coals imported into the Isle of Man from Whitehaven in the county of Cumberland, arranged under the form of two series; the one comprehending ten years from 1781 to 1790, the other including twelve years from 1798 down to 1809. Both statements may be relied on, the first was inserted in a scarce book, the second in a late and though local, most respectable publication often already referred to.
The increased consumption of coals in the Isle of Man will not so much show an increase of population as an increase of comforts amongst the inhabitants at large, the consequence of a more extensive system of cultivation, and the diminishing number of fishing boats that used to take out in the months of harvest upwards of 2000 of the most active inhabitants of the labouring class.
|An account of the coals imported into the Isle of Man for ten years, ending the 5th January 1791.||An account of the coals imported into the Isle of Man within twelve years; viz. from the 5th January 1798, to the 5th July 1810.|
As to the great advantage the inhabitants would derive, were coals to be discovered on their isle, I should entertain some doubt, when I consider that the inhabitants of the city of Dublin have their coals put into their cellars at less expence than the persons who live in the County of Cumberland, twelve miles distant from the coal-pits of Whitehaven. In the present state of affairs in the Isle of Man, any thing, I should apprehend, that would have a tendency to diminish the number of hands that may be employed in extending the culture of the land, would rather operate as a check on the farther improvement of the island itself.
It is very doubtful whether the minerals mentioned here, do really belong to the Isle of Man. They made part of a collection that was in the possession of the late Lord Henry Murray, and were obligingly communicated to me by Mr. Wm. Scott, the Collector of the Custom-house at Douglass. Many of them had no labels affixed to them. The informations I received concerning them, I shall here communicate.
Wolfram, either in detached pieces or fragments, or adherent to quartz: supposed to have been found in loose pieces at the surface of the ground, on the slope of South Bor-roilva, two miles from the mines of Foxdale.
Tin-Stone. Great doubts may be entertained as to its occurrence in the Isle of Man.
Earthy talc. Said to have been found on Mount Murray.
Could we depend on the locality of the earthy talc here, its occurrence would rather favour the possibility of that of tin, as the two substances often accompany each other.
I consider myself warranted to deduce the two following conclusions.
1. That it appears extremely probable that at some period or other, a subsidence to the south of the whole chain “en masse” took place, which caused the three dislocations referred to in the course of this paper, and which are nearly at right angles with the direction of the chain itself.2. That the same subsidence may be supposed to have produced the general dip of the stratified rocks to the southwards.
|Names.||Elevation in feet above
the level of the Sea.
of the Springs.
|Farane-y-phing; pronounced Faraan-e-fing||1264 feet||45° ⅓||Fahr.|
|On S. Bor-roilva slope||undetermined||45° ½|
|Near to the top of Slieau-y-Garnane||960 by approximation||46°|
|Cass-ny-hawin, Head of the river||422||46° ⅓|
|St. Patrick's well; Kirk Lonan||undetermined||47° ½|
|Spring between Glen-Roy and Glen-Laxey||undetermined||47° ½|
|South-Quay Douglass||0||48° ½|
|Pigeon-Spring, on Walberry How||undetermined||48° ½|
|Vinch's well, Douglass-bay||0||49° ¾|
|Kirk St. Ann' Glebe||235||50°|
|Fleshick bay||0||50° ¼|
|Kirk Lonan's Glebe||365||50° ⅓|
|Burchet's well, Calf of Man||undetermined||50° ½|
|Cregga well||undetermined||50° ½|
|Mill-town spring||undetermined||51° ¼|
|South-quay, Douglass||0||51° ½|
|Langness spring||0||51° ½|
|Ball-Fhallack spring, pronounced Balla-Salley, the royal residence||undetermined||51° ½|
|Balla cregga' How||undetermined||52°|
|Douglass-bridge, on the road to Castletown||0||52° ¼|
|Flax-mill Spring||undetermined||52° ½|
|Purl-Keill-Moirrey, Port-le-Murray||0||52° ⅔|
|Mr. Gurley's well; Calf of Man||206||53°|
If we rate at 50° Fahr. the mean annual heat in the Isle of Man, we shall have it differing from that of London merely by 1° for a difference of 2°,41′ of north latitude. Comparing the same annual heat of the Isle of Man with that of Edinburgh, we shall find it surpassing the latter by 2°,2′ Fahr. though the latitude of the Isle of Man be only 1°,45′ more to the south than that of Edinburgh.
The mean temperature of the month of June, 1811, in the Isle of Man, deduced from 128 thermometrical observations, I found to be 55°,81′ Fahr. but as most of the observations were made on the tops of mountains, the mean must be lower than it would have been had the observations been made in the plain. Thus I find that thirty-nine thermometrical observations (out of the series of 128) made by the sea side give for the mean 57°,37′, which when compared to the mean of 22 thermometrical observations made at the apartments of the Royal Society on corresponding days, is deficient by 4°,35′. The London mean being 61°,72′, and that of the Isle of Man 57°.37′. At Belfast the mean is 64°,90′ Fahr. The mean height of the barometer for the same month of June, 1811, is as follows.
|Isle of Man||30.11895|
The frosts are short in the Isle of Man, and the Snow does not lie long on the ground, especially near to the sea. I was informed by the Rev. Mr. William Fitz Simmons, that on the top of Sneifeldt it does not remain longer than two or three weeks, from Christmas generally, to the second or third week of January.
|Names and Situation.||Signification.||Number
|Elevation in feet
above the level
of the sea.
|Baldwin Valley head||1395|
|Balla-cragga how||Rocky farm||44||412|
|Balla-chirrym; about the middle of the range||Dry farm||177½|
|Balla-gawn; about ¾ of a mile south of Kirk-Michael|
|Balla-wodden; about ½ mile south of Kirk-Andrew|
|Beary mountain||Beiree, tops of hills?||27||900|
|Bein-y-phot||The Pot mountain||20||1750|
|Bool-benney; highest ridge on the road from Castletown to Douglass, between the 6th and 7th mile-stone||a place where furze grows||39||538|
|Bor-roilva, Baroil, Barroole, or Bourrul; North||Wild mountain||12||1850|
|Brada-head; high point||47||767|
|Burchets' Hermitage; highest spot in the Calf of Man||49||461|
|Calf of Man; Mr. Gurley's house||206
|Caran-hill||Crown of the head||10||984|
|Cass-ny-hawin; taken a the head of the river||The foot of the river||422|
|Clay-head is the hill that lies N.E. of Banks how|
|Cloven-stone; a Druidical monument, ½ from Laxey, on the Douglass road|
|Corrin's tower; highest point of Peel-hill||34||675|
|Crammag-bridge on Sulby river||452|
|Cregneish or Craig-neash||Neash, rock||520|
|Cronk-ne-liry-Lhaa, or Cronk-ny-irrea-Laa||Break of day hill||37||1445|
|Watershed, between Cronk-ne-liry-Lhaa and S. Borroilva on the road from Castletown to Peeltown||982½|
|Six mile-stone between Castletown and Peeltown; lower limit of the Turbary in that part of the island||692|
|Cronk-Ouyr, or Cronk Owre||Ouyr dun colour
|Cronk-Shamrock, or Primrose hill||hill of tents||5||273½|
|Dun-bridge; at the foot of Dun-how|
|Foxdale or Foxtal mines, central part||32||346|
|Glen-roy, at the Rev. W. Fitz Simmons' house; one of the highest habitations in the island||493
|Gob-y-Scioot, or Gub-y-Scioot||Ghub is point, Water-spouts are called Ghub-ny-spoots?||22||1820|
|Gob-y-vullea, Gub-y-vulley or vollee||Gob, a beak
vully, a height
|Greebah or Greebey, North||Grie, grey||28||1478|
|Hampton House, about 2½ miles from Douglass, on the Castletown road||407|
|Karraghyn, or Karaghan||31||1520|
|Kione Gogan; the hill N.W. of Spanish head|
|Kirk Lonan; Kirk Leonard in the map||365|
|Kirk St. Anne; Kirk St. Agnes in the map||235|
|Laxey-valley-head||Lax-waay or waag
|Middle hill, about 1½ mile from Douglass, on the Castletown road||282|
|Mount Murray; the hill between K. Braddan and K. Marrown||Black hill||742½|
|Mullach Oure; Southern part of||23||1540|
|── Northern part of it and lower limit of the Turbary||23||1378|
|Mullin-y-chlea||The concealed mill|
|Mullin-y-chleigh||the mill on the Boundaries||28|
|Mullin-e-Cleii||the playing mill||
|Peel-Hill, high point||34||675|
|Slieau-Aalyn, or Slieau-Chaillin||Aalyn, beautiful
The Witches mountain
|Slieau-Chiarn||The Lord's mountain||9||1068|
|Slieau-dhoo||the black mountain||18||1215|
|Slieau-Lhearn||the broad mountain||21||1533|
|Slieau-y-Carnane, or Slieau-y-Carnaane||38||990|
|Head of Land, or overhanging cliff between Slieau-y-Carnane and Cronk-ne-Liry-Lhaa||877½|
|Snei-feldt, Snioghtey, or Snawble; great||Snow-field||16||2010
|Boggy Table-land, N.W. of Sneifeldt||1154|
|Upper limit of the arable land, between Little Snei-feldt and Slieau-Lhearn||937½|
|St. Anne's head; low point||43||126½|
|St. John's chapel; the Tinnwald||130|
|Watershed between Peeltown and Douglass||126½|
|Watershed between Purl-keil-Moirrey and Port-Erin||The harbour of St. Mary's church, Irish port||81½|
- Bishop Wilson's Works—Second Edition—Two Vol. fol. Lond. 1782. Vol. I. p. 449.
- An Account of the Isle of Man, by George Woods, London 1811.
- This map however is neither complete nor as perfect as I wish I had been able to execute it. Mr. Wm. Geneste (a gentleman of Douglass, to whom I am much indebted) has had the complaisance to undertake last Summer at my request, a trigonometrical survey of the Isle of Man, conjointly with Mr. James Kewley, a person who has formerly practised as a Surveyor. But I fear the result of their labours, which Mr. W. G. intended with a great liberality to put at my disposal, will not be ready to be published in this volume of the Transactions of the Geological Society.
- The height of Snafield (says the Bishop) as taken by an exact barometer, is about live hundred and eighty yards, the mercury subsiding two inches and one tenth. Vol. I. p. 449.
This is very probably the first application that was made of the barometer in Great Britain to determine the elevation of a mountain. The original experiment pointed out by Pascal, was performed by Perier (his brother in-law) on the “ Puy de Dome,” 19th Sept. 1648. Bishop Wilson came over to the Isle of Man in April 1698, where during his long residence, he made the experiment that led him to the elevation of Snei-feldt.
- According to Mr. J. C. Curwen's calculations, the Isle of Man contains 245,760 Acres. viz.
100,400 of mountain 69,045 for grazing 30,158 in oats 15,079 under barley 14,761 under green crop, 710 of which may be considered as potatoes 9,047 in wheat 7,270 in roads, rivers, houses ────── Total 245,760 Acres
Report of the Agricultural Society in the Isle of Man.—Workington, 1810.
- Very large trees of oak and fir have been found buried in the peat of the Curragh, some two feet and half in diameter, and 40 feet long. The oaks and firs do not lie promiscuously, but where there is plenty of one sort, there are generally few or none of the other.—Wilson's History of the Isle of Man.
Mr. J. C. Curwen seems to think that the area of the flat country comprehended between Ramsay and Kirk-MichaeI, Jurby-point and Aire-point, may be rated at 40,000 acres, that is to say, according to his above referred to calculations, to a little less than 1-6th part of the whole area of the island.
Agricultural Report, p. 158.—Workington, 1810.
- Roms-wazy-wide or roomy bay.
- The miner from whom I received my information is a Yorkshire man, and used the technical word cheek instead of that of side; an expression which I understand is likewise employed amongst the Derbyshire miners.
- This is an expression I beg leave to introduce, and refer to the judgement of Geologists. All the stratified rocks, but particularly those that have been deposited in a rather horizontal situation, are divided by rents perpendicular to their direction, corresponding therefore with their dip, into solids of dimensions more or less regular, and usually similar in the same individual strata. Thus if the structure of a rock be middle thick-slaty, it will divide itself spontaneously into rectangular solids. When the thickness of the strata bears a more equal proportion to the length or respective distance of the dip-joints, the natural divisions will come to a cubical form. If on the contrary, the structure be thin-slaty, the rocks will rise spontaneously under the form either of flags or slates. Whatever may be the shape of these natural blocks, their two contiguous sides are constantly coated with the predominating ingredient of the rock itself in its present state. Thus if the rock be quartzose, the coatings of the dip-joints will be veins of pure white quartz; if it be calcareous, the coatings will be crystallized calcareous spar, but unless we cause artificially the splitting of the rocks to take place, seeing but a vertical or a horizontal section of the coatings, we arc apt to adopt the wong opinion they are veins instead of layers.
- All the Runic or Danish monuments so frequent in the Isle of Man, are (as far as my observation has gone) of greywacke, without one single exception. The inscriptions they bear are said to be written in the old Norwegian language: they are placed on the edges of the stones, whereas the earrings are on their flat surfaces. The latter appeared to me to bear some resemblance to the form of a snake.
- Page 449. Vol. I.
Since the above was written, a letter which I received from Mr. William Geneste of Douglass, answering some inquiries I made, contains the following more precise information on this subject.
“Mr. Fitz. Simmons, who is preparing to publish an extensive work on the ancient History of the Isle of Man, states, that mention is made of the mines of the Isle, in the time of Sir Stanley* 1st and 2d. Those at Brada, he believes, were first wrought; whether those at Foxdale were then opened may be doubted; those at Laxey were opened and wrought by a mining company of Cumberland, about the commencement of the last century.”
“Mr. William Scott of Douglass conjectures, that the mines at Brada were wrought previous to the discovery of gunpowder, from Feather-wedges (a contrivance for breaking asunder rocks, which is now performed by gunpowder) having been found in those mines.”
Mr. William Geneste informs me farther, that he lately found in some books (titled Charge of the Revenue) in the Duke's office, in Douglass (called the Seneschal's office) “ that the last Earl of Derby had the mines wrought, paying the workmen at the rate of £ 3 manx‡; per ton, for the ore (lead) raised. In the year 1709, he paid the miners for about 70 tons; from the year 1709 to 1713, about 30 tons yearly. A new melting house was built in the year 1717. The working of the mines was totally suspended about three years ago.”
* The first Sir Stanley appointed King of Man, was by grant from King Henry 4th, in the year 1407.
‡ The manx money is to the British in the proportion of seven to six.
- An Account of the Isle of Man, by George Woods, London, 1811.
- The Bishop of Landaff states the produce in silver on some Manks ore, to have amounted to 20 ounces in a ton of lead. By some of the workmen it is asserted that the quantity of silver has occasionally amounted to 35 ounces in the ton. Watson's Chem. Essays, Vol. 3. p. 328. 7th Edit.
- Mr. Wood's account of the Isle of Man.
- Mr. Curwen's Agr. Report, p. 153.
- In Mr. Thomas Quayle's “ General View of the Agriculture of the Isle of Man,” it is said that from 1807 to 1811, 84,992 barrels of lime have been sold from the several kilns fitted up for that purpose in the south-eastern part of the island.
- Mr. Curwen's Agr. Report, p. 112.
- During the whole of my excursion through the isle of Man, I had the pleasure of being accompanied by Mr. Thomas Scott, brother to the much celebrated Scotch Poet of that name. Mr. Wm. Geneste, a well informed gentleman, and a native of the isle, joined our party while we were examining the southern part of the isle. From the two above mentioned gentlemen, and generally from all those to whom I was introduced in that island, I received the most ready and kind attentions as well as much information.
- The Report of the Commissioners of Inquiry for the Isle of Man, 1792
- Mr. Curwen's Report of the Agricultural Society.
- The Census of 1792, returned 28,000 inhabitants nearly, but Mr. Curwen observes that all the estimates of the population of the Isle of Man published at different periods, have been much overated. He hardly thinks it can exceed 23,000 or even so much, viz. 6000 inhabitants at Douglass, 2000 at Castle-town, 2000 at Peel, and 1500 at Ramsay, besides 11,000 spread over the islands, considering how few villages there are, and how small their sizes are.
- A chaldron is a measure of 36 bushels.
- Jameson's Mineralogy. Vol. 1. p. 431.
- At Spanish head, on the spot called Kione-Gogan, (a head resembling a noggin) the strata have been rent asunder in two contrary directions. The contiguous sides being now several yards distant the one from the other. The principal rent runs north and south, the transverse one east and west, presenting an assemblage of four large square compartments.
Is this referable to the great subsiding pointed out above? or more likely, to the cause that gave origin to the metallic veins, and particularly to the cross course at Foxdale?
The grey-wacke slate of Spanish head splits naturally into long beams 12 or 15 feet long, it for mantle-trees, and strong enough to bear the weight of the highest stack of chimnies.─Wilson's History of the Isle of Man.
- For the calculation of these heights I have made use of Professor Leslie's Sliding Scale.
- In the trigonometrical Survey, North-Berule, 1804 feet.
- Snea-fell, from the trigonometrical Survey, 2004
Snàfield, from Bishop Wilson, 1740
- Tinnwald from the Danish word Ting, a court of justice, and wald, fenced. It is held on an artificial mount, near the middle of the island, in the open air.