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of man convulsions on record capable of producing effects infinitely more stupendous than those required for the comparatively insignificant purpose of the case before us.

Let us suppose, then, that at a certain time some great convulsion occurred (as the bursting of a lake, violent rains or waterspouts) causing an irruption of waters far exceeding the last, so copious as to raise the level of the descending stream some feet higher than the caves, and at the same time impregnate it with those fine particles of loamy mud which we find deposited in the cave. In fact, a catastrophe, similar to that of modern date, which occurred near St Lucido in Calabria, when the ground is described as having been dissolved, so that large torrents of mud inundated all the low grounds like lava, the swampy soil in two ravines being filled with calcareous matter. We may conceive this moving mass acting with inconceivable pressure on the rocky limestone barrier between it and the plains below, till at length forcing a passage through some weaker part, its concentrating volume burst forth with inconceivable violence, and finally tore up every opposing obstacle. Such was the effect of the pressure of water on a barrier something similar in the valley de Bagne in Switzerland, which I had an opportunity of inspecting a few days after the catastrophe, productive of such disastrous effects for upwards of twenty miles below; and when we bear in mind that limestone ranges are frequently honey-combed, if I may so speak, with fissures and chasms connected with cavernous chambers within, instances of which occur in the very rocks adjacent to the caves before as *; we are not making suppositions unsupported by facts. The consequence of this irruption would naturally be, not only the probable removal of the rocky barrier, but, by powerful erosion, the excavation of the bed of the valley itself, till it had scooped out its course to the level at which it now runs. Whether such an inundation of mud and diluvial detritus in its progress towards the sea may have caused the wide extent of low alluvial land, forming what is now called Rhyddlan Marsh, may be matter for future inquiry;

* At the base of the cliff of Galltfaenan, a stream gushes out from a subterraneous channel, through which it is supposed to be conveyed from a considerable distance.

VOL. XIV. NO. XXVII.-JANUARY 1833.

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at all events, local appearances render such a conjecture by no means improbable. On the final erosion of the former bed of the river now running at the bottom of a still deeper valley, the present upper caves would thus be left high on the façade of the cliffs as we now behold them. It may be argued, that, on the retreat of the waters, the mud injected into the recesses of the cave would have been removed. But two reasons may be urged why this should not have happened: 1st, That in consequence of the very peculiar character of the earthy particles, the laminous sediment would have been deposited in a few hours in so compact and adhesive a state, as to defy any ordinary means for its removal. The particles are indeed so extremely fine, and impalpable and unctuous, that it is almost impossible to separate them sufficiently for the purpose of microscopic observation. Consequently when, in addition to this, the adhesive character of such loamy argillaceous atoms is taken into consideration, it may be well conceived that a very compact deposit is easily formed. So minute indeed are the particles, that 20 grains in two ounces of water, gave the liquid as deep an ochrey colour as a mixture of the liquid and the powder in equal parts, with all the appearance at the same time of being in a state of chemical solution. In two or three hours, however, they subsided, leaving the water nearly colourless, and this, when poured off, left the deposit in the form of a strong adhesive paste. Very few hours, therefore, and still more, if we allow a duration of days, would have effectually choked up the interior of the cave with the compact mass now existing, more particularly, when we further take into consideration that the water admitted within the recesses would have been in a state of comparative quiescence and stagnation, little if at all affected by the agitation of the external stream. 2dly, On reference to the ground-plan, Fig. 1, Pl. II., it will be perceived that whereas the course of the river is at the cave from about N. to S., the portion of the cave entirely blocked up commenced at the north-east corner of the great opening, about 20 feet within, and that its course is to the northward; so that the descending waters would naturally be drained gradually from the injected mud, by no means acting upon it as a disturbing force, probably, moreover, forcing its way and clearing out an upward channel by pressure through the orifices before

mentioned, existing on the southern side of the main opening vault, till it spouted forth at the aperture on the south-eastern side of the cliff, which may account for the trifling appearance of loamy deposition in these passages. I am aware, however, that, on high authority, to which I feel inclined to pay the greatest deference, it has been urged that this loamy stratum is to be attributed not to inundation, but to filtration of earthy calcareous matter through the rocky roof, In answer to this, I would merely remark, that the solid mass of superincumbent rock from 40 to 50 feet in thickness strongly militates against this view, and further, that it receives little support on inspection. For on examination it will be seen, that the upper surface of the deposit has every appearance of having originally formed a compact mass, completely filling up every cranny and fissure to the very roof, though at present there is a void space, varying from 8 inches to a foot between the surface of the diluvium and the roof. Now, if the sediment had entered by filtration, this surface must have followed the laws of gravity, and formed a line parallel to the present horizontal strata observable in the mass of the deposit; but instead of so doing, it follows the irregular sloping of the roof, which dips to the north at a small angle, as if the upper portion of the mud had gradually and uniformly collapsed into its present inclined position, just as the muddy deposit near Laureana, quoted by Mr Lyell, vol. i. p. 427, is said to have collapsed to the extent of 10 palms. It would be presumptuous to express any positive opinion as to the probable origin of these caverns, so frequent in the limestone ranges, in the face of the many ingenious conjectures of more experienced geologists. It is, however, worthy of remark, and will be easily seen on reference to the sketches, that although the general character of the whole upper line of stratification in the cliffs from its southern extremity at Cefn to its northward termination, are horizontal, yet, at the level of this cave, and near its aperture, the beds of limestone have a visible curve upwards, as if some sort of pressure had dislocated or bent the weaker joints of the cliff, and thereby enlarged, if not actually caused, the cave under consideration.

For the information of those who may be induced to visit this spot, as attractive to the artist from its picturesque beauty, as

it is interesting to the lover of science, from the circumstances I have endeavoured to detail, I shall add a few directions which may be found useful. I have mentioned the bluff of Galltfaenan as forming a striking feature in the pleasure grounds of Col. Salusbury, on the crest of which has been erected a summer house, commanding in front a bird's eye view of the whole valley through which the river Elwy runs, affording at the same time on the left, a partial view of the narrow gorge confining the brook Meirchion, and on the right, the progress of their streams through the aperture supposed to have been formed by the removal of a continued line of rock, connecting this with the opposite cliff of Cefn. From this point, the main opening of the upper cave is not seen, being concealed by the projecting portion of the cliff, by the base of which, the road passes the perforated rock forming the lower cave; but the aperture alluded to as communicating by subterraneous channels with the main vault of the upper cave, appears immediately in front. features are represented in Fig. 2. of Plate I.

These

From Galltfaenan, the real distance, as the crow flies, cannot much exceed a quarter of a mile; but on account of the river intervening, which is not at all times fordable, it is necessary to take a circuitous route, either by returning to the main road from St Asaph, down a very steep carriage-road, or by descending a winding path cut by Col. Salusbury, leading to the foot of his cliff near to the mouth of the subterraneous stream, alluded to in note p. 49, which bursts up with a plentiful supply of water, not certainly equal in degree, but similar in other respects, to the reappearance of the river Mole near Dovedale in Derbyshire. This path leads to a small bridge called Trap-bridge, over the brook Meirchion, on the high road above mentioned, which runs parallel to the Elwy, and immediately opposite to the west front of the Cefn cliffs, commanding an admirable view of the whole line of stratification, as well as the apertures of the upper and lower caves. The river is crossed at the small village of Pont Newydd, so named from its bridge built by Inigo Jones, whose family it is said came originally from this neighbourhood. This road, after crossing the bridge, diverges to the right and left, the latter leading towards the great turnpike-road from St Asaph to Abergele, while the other branch turns towards the lower

or perforated cave-rock. A winding path, however, meets this part of the road, by which there is an easy ascent to the upper cave. A new road is also now forming by Mr Lloyd, with great taste and judgment, along the side of the cliff, near to which, and at no great distance above it, and about half a mile from the upper cave, another excavation in the rock presents itself, which, on examination, I found to be entirely blocked up with soil, and has clearly never been open to human observation. But I have no doubt, from its appearance and character, that it will prove closely analogous to this which has been the subject of the present communication, and will therefore, there is every reason to believe, exhibit as rich a prospect, whenever its recesses may be explored, in search of those organic remains of animals now unknown in the temperate zɔnes. These roads and the situation of the caves shewn in Fig. 1. of Plate I.

On the Silicification of Organic Bodies *. With a Plate. By Baron LEOPOLD VON BUCH.

FROM the lively intercourse of naturalists with one another, it has happened that a number of minute observations have become far spread and well known, before any public mention has been made of them. Every communication of such observations, when made by persons of ability, will assume another form. Either one has to add other facts to those originally discovered, or knows how to place these same under other points of view; and thus give a new, more comprehensive, and detailed account of them, from the observations which they suggested. Then it is often difficult, perhaps impossible, to trace back to their origin the individual facts and observations, which at length afford rich and fruitful results. The priority as to the original discovery becomes lost, the more easily, that in general it cannot be at all foreseen what may arise out of an apparently trifling discovery in other hands, or whither it may lead. But true naturalists have never cared much about priority of discovery such a feeling would disturb every sort of fellowship. It would be easy to imagine that the germ of important discoveries

* Read in the Academy of Sciences (of Berlin) upon the 28th of February 1828, and translated from the German original by George F. Hay, Esq.

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