CHAPTER XI. GEOLOGY AND MINERALOGY OF THE CHANNEL ISLANDS. MODERN DESTRUCTION AND RENOVATION. THE magnificent scenery, so much admired on the coast of all the Channel Islands; the wild desolation that reigns when the receding tide lays bare needle points, or exhibits alternate floors and walls of granite, in places where a few hours ago the water presented a smooth, but treacherous surface; the broken cliffs, detached headlands, natural arches and recesses, and gloomy caverns; the grotesque rocks, some prominently jutting out, some fallen from above and angular, some rounded and smooth; -all these are the results of an action of wind and water that is going on every year, winter and summer, and that is always tending to reproduce, with little essential variety, the very forms and outlines it is constantly destroying. Scenery representing these picturesque appearances, is pictured with great accuracy in many of the illustrations in this volume.* Such * See more especially the following views:-Cliff and Roche Pendante in Alderney, Chapter I. Gouliot Rock in Sark, Chapter II. Various views of Jersey in Chapter III. The Corbiere in Guernsey, Chapter X. chapter. The Burons, Chapter XII. The rocks in the The views in the present Chapter XIII. St. Catherine's Bay, Jersey, Chapter XVIII.; and the Coast Scene in Guernsey, Chapter XIX. These have all been selected and drawn with a special view to illustrate the wild coast scenery of the principal islands. SUBTERRANEAN FORCES. 277 representations are not the less valuable because in a few years they must refer to things of the past, for there will still be in the same, or some near place, a similar specimen of rock scenery, produced on similar material by identical causes. To understand the secret history of the picturesque in these islands, it was necessary that the nature and origin of the rocks should be in some measure learnt, and in the last chapter it has been attempted to give a brief outline of these. It remains now to consider the modern changes, the forces now at work, and the result of their combined agency in our own, or very recent times. In all this, however, we must speak in geological language. What is meant by modern and recent, is very old in comparison with human records, and dates back to a time, when, if men existed, they belonged to races long extinct; races, whose only remains hitherto found are fragments of broken flint or harp stone, wherewith savages might perform those few actions that proclaim their human intellect. The modern influences we allude to in this chapter are several ; they include subterranean movements, producing slow upheaval or depression of large tracts; the destroying and reproducing action of the waves in breaking up hard rocks, and accumulating the debris at a distant point; the action of rain and changing temperature; and the action of organic life, modifying in various ways the inorganic forces. That there are forces of the kind just mentioned, the reader, not accustomed to geological investigations, must take for granted. Proofs of them exist in abundance; but it would involve explanations not justified in a work of this kind, to present them to the reader. They are readily found and all the results mentioned are every day events in nature. Assuming then that the syenites and porphyrics of the Channel Islands, covered, perhaps, at one time, with numerous and thick deposits, have been slowly brought into their present position, the sea all the time acting on the uprising mass, and clearing away the softer matter, so as to bare and denude the surface, we may imagine a time when the various operations were less advanced than at present, when the lands were larger, and when they were more nearly connected with the continent. The first class of changes we have mentioned, includes those resulting from subterranean movements of elevation or depression. One of the most familiar illustrations of the existence of such forces is seen in the earthquake, a phenomenon common enough in various parts of Europe, and not unknown in these islands. Many have been recorded within the last thousand years, and many more of smaller magnitude have certainly taken place. In the History of Guernsey, by Mr. F. B. Tupper, it is stated that an earthquake of serious magnitude, producing great destruction, took place in the month of March, 709, and another, or rather a series of movements, between the 22nd and 29th October, 842. On the latter occasion, there was throughout the north of Gaul an accompanying subterranean noise, lasting seven days, recurring several times a day. Afterwards, in the year 1091, very severe and disastrous shocks were felt in the islands, and at Angers, on the Loire, stones were thrown from the arches of the windows of the large tower of the church. Two years before there had been serious concussions in England, and in 1161, the whole shore of the Cotentin was disturbed, the islands being also greatly affected. There are no records of disturbances in the islands from that time till 1843; but, for several centuries, shocks were so frequent, and the mischief done by them so notorious in England and in France, that there can be little doubt the intermediate sea-bottom must have been affected.* At the There is a curious notice in a MS. in the British Museum, apparently referring to a severe earthquake shock in the sea off Sark, that must have occurred at the close of the seventeenth century. The year 1691 was remarkable for severe earthquake action in the Atlantic. EARTHQUAKE ACTION. 279 close of the year last mentioned (22nd December, 1843), a vibration was felt in Guernsey, lasting four seconds, shaking buildings, and ringing the bells of the churches.* Ten years afterwards, in 1853, on the first of April, there was a distinct shock, not injuring property, but causing great alarm. It is evident, then, that there are causes capable of producing elevation or depression, producing their effects from time to time beneath these islands. Their effects must be sought for in distinct phenomena, involving movement of this kind. The earthquake action that has continued at intervals for more than a thousand years, is not likely to have commenced at the beginning of this period. On the other hand, it may have been much more active in former times than it is now. A beach, consisting of rolled pebbles, arranged as beaches are now arranged, placed at the foot of a cliff, but now at an elevation many yards above the highest point to which the tide ever now reaches-is called a raised beach, and is a standing proof of subterranean action of the nature of elevation. Indications of raised beaches in all the islands are numerous, The following description of this shock is extracted from a Guernsey local paper, published at the time, and preserved by Dr. Hoskins, to whom the author is indebted for the reference. "The shock was felt in all parts of the island, and everywhere appears to have produced the same effects. Persons out of doors felt the earth heave under them; in some cases so violently, as to oblige them to lay hold of the nearest object for support. The banks and hedges of the fields were seen to be in motion, and in the houses the furniture and goods were rocked and shaken. Buildings of all kinds were distinctly seen to heave and shake, as well as the pier walls, the iron railings at the south-west corner of the quay, and the massive quay at St. Sampson's harbour. The vane of the town church was violently agitated, and the bell struck twice. The shock was felt in all the other islands at the same time as at Guernsey." The shock was also felt by vessels in the roads, and by a fishing boat at anchor, half a mile to the south of Guernsey. This earthquake was preceded by a very remarkable meteor, and the appearance of the sky is said to have been very unusual. A brief notice of this earthquake, communicated by Dr. Hoskins, is published in the Abstracts of Papers read before the Royal Society, Vol. V., p. 498. but it will be sufficient to describe some about which there can be no question. One such was discovered while cutting a deep trench through the granite in constructing the works at Fort Regent, in Jersey. It is in all respects clear and satisfactory. About thirty feet above the present mean level of the sea, there are the remains of a beach, precisely identical with beaches now at the sea-side. These include a thickness of some yards of well-rounded granite boulders, some of large size and considerable weight, reposing on a smooth surface of rock. The beach gradually thins out towards the sea. Any one may see the state of the case, as a good section made by a road cutting is within the town of St. Heliers, but it will probably be obliterated before many years are past. In Guernsey there is a similar, but less perfect beach, in the Island of Lihou. A remarkable instance of ancient beach, mixed up with modern detritus, occurs in Moulin Huet, where a crevice conducting to a cavern is partly filled, and the walls are plastered over by numerous fragments of raised beach, consisting of rolled pebbles and large angular rocks, mixed with smaller rocks and mud, fallen in from a height of at least thirty or forty feet above the present high water mark. Still nearer the town of St. Peter's Port, near the cliffs of Havelet, there are rolled pebbles with angular rocks under similar circumstances. In the island of Brechou, between Sark and Guernsey, on the side of the road leading up from the only landing place to the farm, the road-side cutting has laid bare a particularly clear example of true raised beach, with rounded pebbles. Here, also, the elevation is about thirty feet; but as the quantity of material is limited by the narrowness of the space, it will not be retained long, now that it is exposed to the action of the weather. On the north-western side of Alderney there is a considerable talus of angular fragments, some part of which, perhaps, is merely the decomposed surface of the granite itself, unmoved; but the rest, no doubt, consists of similar fragments fallen down, |
