[from Descriptions of the Western Isles, 1819]
* See the Map.
THE general position and dimensions of this island are sufficiently known to render unnecessary any further information on this subject than that which is to be procured by inspection of the map ; the more so, as it remains one of the most imperfect parts of British geography, and a minute detail of particulars would therefore be merely a pretence to an accuracy which is unattainable. Fortunately, its geological details are so simple, and the limits of the rocks which compose it are so easily assigned with that degree of precision which is sufficient for an account of this nature, that, as far as the present objects are concerned, there is no reason to regret the imperfections of the present Map.
The Isle of Man is naturally divided into two distinct portions, as dissimilar in their general appearance as in their structure ; the southern, and by far the larger part, consisting of an irregular group of mountainous land, and the northern, presenting an alluvial tract, for the most part flat, and in many places so level as to admit with difficulty of a sufficient drainage for the purposes of agriculture. The characters of the shores correspond, as might be expected, with that of the surface ; being smooth and even where they bound the northern division, and rocky and indented, with few exceptions, throughout the whole of the larger southe district. Some variety nevertheless occurs, even in the shores of the northern division ; since they terminate abruptly on the west side of the island by earthy cliffs while on the east and north, they descend more gently to the gravelly beach which surrounds them. These distinct characters have doubtless been produced by some difference in the present and former action of the tides on those shores, which it would neither be very easy, nor perhaps very useful, to ascertain. The natural consequence of such a varying action is a variation of the sea-line boundary, which appears however to be of little moment ; while, at the same time, it is far too common a phenomenon in similar cases to require particular notice. From Ramsey to Douglas the eastern shore is rocky, with no exception but that of the sandy tract in Douglas bay. The cliffs are generally high and abrupt, and the sea in most instances skirts their bases, seldom allowing. access to the shore for boats, except in the few places where creeks are found at the mouths of the small streams that flow down the eastern declivity of the mountain land. The valley of Laxey presents the largest sinuosity in this tract, forming a safe and convenient harbour for the boats employed in the herring fishery for which this island is so noted. The forms of the cliffs are determined by the direction of the beds, or at least by that of the fracture of the schist which constitutes them ; and as their inclinations vary, so do their general effect and picturesque appearance, although these are seldom such as to render them interesting to the eye of a painter : they do not appear often to exceed 200 feet in elevation. The same character continues to Derby haven with little variety or interest ; but at this point a sudden change takes place; the shores, although still rocky, becoming flat, and maintaining that character, with some variation from sandy beaches and rocks more or less elevated, as far as the southern side of Port la Marie point, where they again become abrupt and high, as on the eastern side of the island. Near Spanish head, the sections of the cliffs are vertical, and as they attain an altitude apparently not less than 300 feet, they assume considerable grandeur of character ; the breadth and simplicity of fracture which they present, materially enhancing that effect, for reasons which need not be suggested to those conversant in the principles of art. Here also a circumstance occurs, of some interest to the geological as the general traveller.
Large portions of the land have been separated by vertical fissures extending from the surface almost to the level of the shore beneath, so deep and so dark that the eye does not penetrate to the bottom. The principal masses have thus slid into new positions, while many smaller fragments appear still suspended in very act of falling ; even the larger, seeming to be often so nicely poised that the hand would almost be thought sufficient to push them from their present situation into the sea that rolls below. The spectator who does not walk with fear over these chasms, must at least walk with caution ; and will not perhaps at first easily divest himself of the sense of insecurity with which he traverses ground that appears in the act of escaping beneath his footsteps. In a physical view, the phenomenon is however much too common to require any explanation ; while it is obviously a slide of no very distant origin, geologically considered. As an historical occurrence, it is of considerable antiquity ; and although the distance in point of time cannot be ascertained, its lowest limit is recorded by the existence of a Druidical structure on one of the moved fragments ; a chronological index, at least very remote, if not exactly to be assigned.; The narrow and rocky channel which separates the Calf from the main island, with the boisterous tide that runs through it, and the high rocky shores that extend from this point to Brada head, will present much interesting scenery to those who may examine them from below although from above, the points of sight are seldom picturesqiue Hence to Peel, the same character, but with less grandeur, is preserved ; after which, lower and less striking rocks, of different aspects, continue with some interruption to skirt the shore till the mountain land terminates in the alluvial tract already described. The castle of Peel, more conspicuous for the extent and variety of its outline, than for the magnitude and style of its buildings, with the picturesque situation of its harbour and town, and the life produced by its shipping, forms an interesting object wherever it is visible in following this line of coast.
The general aspect of the interior of the island, is consonant to that of the coast now described. The northern alluvial tract is, throughout a great part, flat, while it is also in a high state of cultivation. One irregular range of low hills, formed of gravel, sand, and other similar matters, extends in a curved line along its northern and western edges ; and I need scarcely add that, as it possesses but little wood, it offers no beauty to the travellers eye beyond that which arises from the aspect of fertility, and from that of a scattered, and apparently wealthy, rural population. This indeed is a circumstance which will forcibly strike the English observer, who is accustomed to see large tracts, even when in high cultivation, occupied by a few opulent tenants whose houses are scarcely visible in the agricultural waste : it displays the remains of a system not yet conformed to that which is now fast establishing itself through the most improved parts of the British dominions. The features, whether of the mountainous or of the hilly tracts which form the elevated and southern part of the island, are various ; but the two are in general readily distinguishable by the presence or absence of cultivation ; although that has been here extended as far, perhaps in some instances further, than prudence would have dictated, or profit will ultimately justify. From the summit of Snaefell, which is the principal elevation of the Isle of Man, a tolerably accurate idea may be formed of the general distribution of the mountains, and of the relations of the several parts of the group. This mountain, as it has been ascertained by trigonometrical observations, is 2004 feet high, and is accompanied by numerous other elevations gradually declining from that of North Barrule, the height of which is 200 feet less, down to the shores on each side of the principal group.
Notwithstanding the apparent division above alluded to, I must remark, that no real distinction exists between the hilly and the mountain land, since the latter declines into the former without break or interruption, by a succession of undulations becoming gradually lower as they approach the shores of the island. The forms of the mountains are invariably rounded and tame, as is most frequently the case in the schistose districts of Wales and Cumberland, and the rock is very rarely seen protruding so as to form abrupt faces ; never in such a way as to give a rugged outline on the sky. No difference worthy of notice can be traced in the relative rapidity of the declivities on any of the hills which constitute the group ; nor do the few broken faces which are to be seen, appear to respect one point of the compass rather than another.
On the north-eastern side of the island, the descent appears indeed more rapid than on the other parts of the group ; and the difference is very remarkable if we compare the declivity which lies between Laxey and Ramsey, and includes St. Maugholds head, with that which descends towards Douglas, Peel, or Castle Town. But this. circumstance does not affect the validity of the preceding remark ; since it merely arises from the truncation of the group, (if it may so be called,) by the sea at this end of the island, being nearer to the highest elevations, and consequently from the, absence of those lower hilly tracts which, on the other sides, skirt the, principal mountainous district. In consequence of the gentle slope of this elevated land, the mountains are, as might be expected, wet and boggy ; a covering of peat, amounting on an average to two feet in depth, appearing to invest most parts of the elevated region. Except the Lycopodiurn alpinuin and selaginoides, it produces no Alpine plants, and with the exception of Ophrys cordifolia, not a rare one to gratify the botanists curiosity and vary the dreary uniformity of the surface.
The view from the summit of Snaefell is remarked for including the several parts of the British dominions; the ranges of Snowdon and of Cumberland being visible to the eastward and southward, the mountains of Morne, and Fairhead appearing on the west side, and the Mull of Galloway with the elevation of Criffel rising in the northern horizon. A distinct view of the island itself is also obtained ; although the shores are in several directions excluded by the height of those hills which approach in elevation to the parent mountain. It is more interesting to the geologist to trace from this point the relations of the different hills to each other. Although the whole southern division of the island constitutes one group, it is evident that the several elevations are disposed in a linear direction, lying from the N. E. to the S. W. and thus forming a principal chain, with one inferior ridge on each side declining from the central line Of the accuracy of this line the eye is not a competent judge, but it appears to extend in a very even manner between the points named. Hereafter, it is to be hoped, the construction of an accurate map will enable us to determine more precisely, that which can now be only described in a general manner. The positions and directions of hills, and more particularly of those which consist of stratified rocks, whether primary or secondary, and the relations which these bear in their several parts to the original positions of the strata, form an important question in physical geography.
The three main elevations which determine the position of the central chain are, Snaefell, North Barrule, and South Barrule. Ben y pot, North Greebah, South Greebah, Carraghan, Sartyl, and others, all lying between 1600 and 1300 feet of elevation, and more or less accurately in the same line, appertain to the same elevated and central range, which declines gradually, at the north-eastern end, in Cronk dhu, and at the south-western, in Slieu y carnan. The summits of these several hills do not however rise materially above the ridge itself which connects them. The inferior ridges which on each side decline from this leading one, are prolonged in directions tolerably parallel to it, with such deviations as might be expected, until they terminate, like that, in the shore or in the flatter tract of Castle Rushen division. Mullachoure and Slieu learn, each of them reaching to 1500 feet, or upwards, are the most elevated points of the south-eastern of these ranges, while Carden, Slieu dhu, and Caran form the chief prominencies on the north-wesern side. Neither of these ridges however is strongly distinguished from the central one ; each being connected with the principal by high land, in the same way as the predominant summits in all the three ridges are by the intermediate parts. The transition from these higher elevations to the hilly land beneath, is gradual and imperceptible as I have before remarked ; no criterion being present to distinguish them, except the very irregular one formed by the boundary of agricultural improvement. The lower undulations are numerous and irregular, reaching the sea on all sides, except that which is bounded by the northern alluvial tract, and that where the flattish country forming Castle Rushen division intervenes. Scarcely a level spot of any extent is to be found throughout the whole of this range ; the undulation of the ground being uninterrupted and the hills succeeding each other with only small valleys interposed, the predominant tendency of which is at angles to the leading ridge. This part of the the country is covered with inclosures, with scattered farm houses, and with cultivation ; which, cramped as it must always be in a certain degree wherever small farms constitute a principal portion of the allotment of the land, is in every respect on a par with its state in those districts of England where a similar division exists. The few trees which are to be found in the island, are to be seen chiefly in these valleys ; and, thus sheltered, they thrive as well as in other similar situations on the western coasts of England. Whatever defects in this respect the island displays, have arisen from the neglect to which that branch of rural economy has been subjected almost every where throughout the British dominions until a recent period ; and, here as elsewhere, they will be in time removed by the exertions which are making to restore this important part of the management of land to its due rank in rural affairs. Pleasing scenes, rarely such as can be styled picturesque, occur every where in these sheltered valleys ; and when, in the progress of time, wood shall become more predominant, the Isle of Man will, yield little in beauty to those parts of England or Scotland which are not characterized by the striking features of Cumberland and the Highland districts, or the extended magnificence of Kent and Somersetshire.
The valleys thus described, are not prolonged in their courses, and make no remarkable intersections in the mountain group. But there is one long valley between Douglas and Peel by which it is completely intersected, being at the same time divided nearly in the middle, and at right angles to the direction of the chain. The rivers of Peel and Douglas, collected in this valley, run to the sea in opposite directions. It is almost every where very narrow, the sides rising somewhat suddenly on each hand to the mountainous or hilly land by which it is bounded. At Peel, and still more remarkably at Douglas, it terminates in the sea by a narrow valley, producing at the former a prolonged basin which, by the erection of a parallel pier, has been converted into an excellent harbour for small vessels : at the latter is erected a double pier inclosing one of the best dry harbours in the Irish, channel.
From this disposition of the land, the rivers of.the Isle of Man are, as might be expected, rather numerous than extensive in their courses. Every small valley produces some stream, discharging itself into the sea or increasing the strength of some neighbouring river. Many of them are consequently too small to require notice, although from the prevailing moisture of the climate, they are rarely dried up. The altitude of the mountain land is sufficient to intercept the track of the clouds during the greater part of the year ; while its western position and insular situation ensure an almost constant supply of rain. The principal river of the island rises by numerous branches from the declivities which surround Snaefell, and passing in a tortuous course by Sulby, is discharged into the sea at Ramsey. The Bright river, which joins the Blackwater to form the inlet at Douglas, the rivers of Castletown, of Peel, of Laxey, and the Santon,1 which marks the boundary of the limestone district on the eastern side, are the next most remarkable streams ; but like the smaller, which it is unnecessary indeed even to enumerate, they require no particular description.
There is no reason to imagine that the form of the land has been any where materially modified by these rivers. If there is any one, the corrosive action of which might be suspected, from the depth and perpendicularity of the rocks which bound it near the termination, it is the Santon. But even this ravine may with equal facility have been determined by the position of the schist, in the same way as the irregular and undulating surface of the land has been. The rivers of this island have little power, and do not appear to have been concerned in effecting the present irregularities, which are more easily referred to the same distant but unknown operations by which the mountains themselves assumed their existing disposition. In a few instances, and perhaps most remarkably at Laxey, from the steepness of the declivity and the rapidity of the water, a quantity of rubbish, forming a beach of rounded pebbles, has been accumulated at the mouths of the streams : but it is generally insignificant in extent ; making no permanent addition to the land, and producing no effect in changing the forms of the shores at the exits of the water. The operations of the mountain streams in some situations, and among others in the higher parts of Baldwin valley, upon the mountain alluvia, is rather more remarkable ; since they are in these places skirted by the flat terraces of rubbish which so often accompany the course of a river that cuts its way through these accurnulations of loose materials.
These alluvia are found on the lower parts of the slopes of the hills and in the bottoms of the valleys, all over the island. Their origin cannot apparently be traced, either to the present or former action of rivers ; since they are equally deep and predominant even where water could never have flowed. Nor is there much evidence of a diluvian origin, a cause, the operations of which are so frequently to be traced in the mountainous parts of Scotland as well as on the great plains of England ; and which may perhaps have given rise to another deposit in this island that will be immediately described. Such however may, at least in some degree, have been the origin of many of these and similar alluvia ; for which, the gradual wearing and descent of the surfaces and summits of the hills towards the valleys, offer but an inadequate explanation. Without such a general cause, it is impossible to explain the existence of granite boulders ; nor indeed of the rounded materials which enter into the alluvial .deposits together with the angular fragments that appear to have undergone but a limited transportation ; which latter, from their similarity of texture to the neighbouring rocks, appear to lie nearly in the places where they were formed. But I must leave this difficult question undetermined, and turn to another of the conspicuous parts of the island where the operation of such a cause seems far less doubtful, nay, even probable.
This is the northern flat district already noticed in the general description, including the Curragh and the Balla chyrrim hills, and terminating on all sides in a shore of pebbles, or in an abrupt face of clay, sand, marle, and similar loose materials. There can be no question that such deposits have been formed from the ruin of solid rocks at some distant period ; and nothing that is visible in the present structure of the land, nor any thing that can be imagined of its former shape, will justify us in supposing that the deposit in questioii has been produced by rivers formerly flowing from the summits of the present hills, or of any hills occupying their position. The presence of granite and porphyry in this alluvium, substances scarcely existing in the island, prove that they have been brought from distant points. If even any imaginary former altitude of the present mountains be assumed, the well known laws which predominate with respect to the relative positions of rocks, do not permit us to assign a place for the granite whence the granitic fragments should be derived, had they resulted from the decomposition of former mountains existing in the island. It will hereafter be seen, that the low position and small extent of the granite in this island, prevent it from offering an exception to the conclusion here drawn.
It is more probable that the alluvium in question has been the result of a general diluvian action, directed from the south towards the north, nearly in the present line of the channel which separates England from Ireland. Thus the deposit has been formed under the shelter of the hills ; having been subsequently modified, in all probability, by various causes of more tedious operation ; namely, by the effects of the tides, by the action of the currents as their position becomes gradually altered in consequence of their owli attacks on the yielding materials of the bottom, and by the usual waste and change which result from atmospheric actions and the gradual corrosion ofrivers. At the present moment there is proof that the actions of the tides or currents are changing the form of the bottom. Sensible alterations are now taking place in the submarine banks which occupy the western channel between this island and England ; and as a new one appears to be in the act of forming, according to the reports of those who navigate these seas, similar actions may have changed the general shape and outline of this alluvial tract from what it originally was, and may hereafter effect in it further alterations.2 It was with a view to the position of this alluvium, indicating a current to the north-wards, that a doubt was expressed respecting the diluvian origin of the deposits which occupy the interior valleys. They should in this case have respected the general current, and predominated in the same manner on those parts of the hills, which, as far as that current was concerned, maybe called their lee sides. The observations are not easy to make, perhaps they have been ill made, and it is therefore possible that the intricacy in the arrangements of the hills and valleys, may have prevented this tendency from being conspicuous, while posterior waste may also have obliterated the small traces of them which once existed.
The substances which form the tract now under review, consist of marie, clay, sand, and gravel ; neither of which are so interesting, either in their positions or details, as to require any very particular notice. The former is successfully used in agriculture ; consisting of a mixture of clay with calcareous earth, and in some cases with frag ments oflimestone as well as of sand and mica, the ruins of those primary rocks which furnished the argillaceous ingredient. Shell marie does not appear to exist, and, in every case, the calcareous ingredient seems to have arisen, like the others, from the destruction of limestone rocks. The position of this calcareous ingredient, particularly where it occurs in fragments in the clay, is in some cases remarkable, and equally with the transported granite, points to a foreign origin. This is the case, among other places, in the alluvia in the vicinity of Douglas, where fragments of limestone are found imbedded in a position superior to that of the calcareous beds which occupy a tract on the southern side of the island. From this cause, among others, the clay of the Isle of Man, forming the basis of the soil which predominates in the cultivated districts, derives its excellence, and for the same reason it is generally rendered inapplicable to the purposes even of the coarsest pottery ; the bricks formed from it cracking in the fire, in consequence of the calcination of the limestone.
The larger boulder stones, which are dispersed over the Isle of Man in various places, undoubtedly owe their origin to the general cause already stated, which they tend at the same time to confirm. Granite is the predo minant substance among these, the different blocks pre senting different varieties in composition. They are not often of very large size, but are cut by the inhabitants for millstones and for pillars, wherever they are of sufficient magnitude and in accessible positions. Between Lay and Ramsey, in the neighbourhood of the Doon river, they appear to have resulted from the ruin of the granite which is there found in situ, since they possess an absolute identity of composition with it, and differ from those which are scattered over other parts of the island. As they lie on the face of the hill above the present visible part of the fixed rock, it is probable that this granite extends to a much greater hcight in the mountains than can now be ascertained ; and that some portions of it might be found higher up, uninvested with the schistose rock, if it were possible to rewove the dense mass of alluvial matter by which it is covered.
Besides the granite, a few blocks of micaceous schist may be seen in one or two places ; but of such a nature that they may possibly be portions of the hills on which they lie, since the intermixture of clay slate and micaceous schist is by no means uncommon, as may be deduced from several parts of the preceding descrip tions.
Such are the most interesting phenomena which relate to the alluvial matters found in the Isle of Man, and such the very slender train of reaspning towards the establishment of general results, which may be deduced from them. But various other extraneous and transported substances occur in different parts of the island ; and as the account of them is too little interesting to require a separate section, it will be preferable to make cursory mention of them here. Whether such substances, gene-rally found on the shores, have been brought among the ballast of ships, or thrown up by the wash of the sea, froiti distant rocks, is almost equally indifferent for the purposes of geology.
The scattered masses of different porphyries which are seen in considerable abundance on the north end of the island, must perhaps be referred to the general cause which deposited the alluvia ; since they are also found, although very sparingly dispersed, in different parts of the interior. Several modifications of hornblende schist, and of argillaceous schist with distinctly imbedded crystals of hornblende, occur also in similar situations. It is even possible that the numerous ~ substances, which are now only to be seen on the shores where the tide washes them up, are the remains of the general alluvial deposit, thus brought from their submarine habitations, like the jaspers and agates which abound on the eastern coasts of Scot-land. The greatest variety of these rolled pebbles is to be observed on the western shore, and they abound in the vicinity of Peel. Jaspers of various colours, quartz, porphyries, and granites, are the predominant substances. Pebbles of chalcedony, similar to those formed in trap rocks, are also to be seen, and these are collected by the natives for the purposes of ornament.
1 A corruption of St. Ann.
2 While on the subject of those changes which the action of the sea appears to have produced on the outline of this island, it is necessary to mention the discovery of a submerged wood in Pool vash bay. This was observed after a violent gale froìn the south, which, by removing the sand, disclosed the remains of a forest lying in a horizontal position, the trees having fallen towards the shore. Their nature could not be ascertamed, as the texture of the wood was nearly destroyed; but it was said to resemble cedar in colour and softness. It might have been some harder wood which had undergone this change by the progress of decoinposition. The phenomenon itself is not of uncommon occurrence, and, if its existence here cannot be satisfactorily explained, we must recollect that it has in other situations been attended by equal difficulties. I need not remind geologists of the other cases which have been recorded, nor of the speculations which have been resorted to for explaining some of the most obscure examples.