At the defile of Niscle, that is to say, at the height of two thousand five hundred and sixteen metres, or one thousand two hundred and ninety-one toises, the surface is covered with verdure; and the potentilla lupinoides, of Willdenow, and the ranunculus montanus, of the same author, are both found in abundance here. These two plants are constantly Alpine in the Pyrenees; the first particularly so perhaps, if it is really different from the potentilla valderia. At one hundred and fifty or two hundred metres higher, appeared the ranunculus parnassiafolius; this rare species is very common here. I remarked that I met with it but three times in the Upper Pyrenees, and then always in situations of precisely the same elevation. Above this station, and until you reach the upper terrace, all is permanent or moveable wrecks of snows; but at the terrace vegetation re-appears: and there are even some grasses, and common saxifrages to be met with. A check however is once more given to vegetation by the great glacier; yet upon rocks under the shelter of the peak, hard and naked as they are, you discover a species of turf of saxifraga groenlandica et androsacea, and some tufts of the artemisia rupestris of La Marck; these plants are small but vigorous; after all, I have gathered round the peak a cerastium, considered by many botanists as the alpinum of Linnæus, and the aretia alpina with rose flowers, drawn by Jacquin; they were both in their highest bloom, and never did I behold the latter in so much vigour and beauty. These latter plants grew so near the summit, that one cannot doubt but they would establish themselves there but for the moving fragments, which invincibly, as it were, repulse them; the lichens even will scarcely fasten to these fragments, and I could but distinguish a few of those of the nature of crustaceous lithophages, which every where have a disposition to fasten on stones of this species. However the most perfect plants which take growth at the greatest height and under the same latitude are those which I have just particularised. The platform and its immense clefts were now what remained for me to explore. I reached Gavarnie on the 20th August, and on the following day passed the port, the less elevated, the easiest and most frequented passage over this part of the Pyrenees, notwithstanding it is found to be, by the measurement of some engineers, one thousand one hundred and ninety-six toises high, and the mean of two barometrical observations, varying but little from each other, fixes it at two thousand three hundred and twenty-three metres, which is not more than seven metres less; hence it is evident this defile as much exceeds St. Gothard in elevation, as the Port de Pinede does St. Bernard; and in fact the great mass of the Upper Pyrenees, exceed in height that of the higher Alps, although the elevations of the peaks which command them, are much less. I now descended to the Spanish Hospital of Boucharo, in elevation corresponding with that of Gavarnie, viz. one thousand four hundred and forty-four metres or seven hundred and forty-one toises. Here I found the platform which rose upon my left absolutely inaccessible, and consequently found it necessary to range the valley of Broto, to discover if possible an entrance into some of the clefts; in our search we arrived at Torla, a considerable village at about a league and a half distance from Boucharo; here I perceived to the east an opening into a large valley, which penetrated into the platform, and which is known by the name of the Val d'Ordesa, and entirely uninhabited, I made my way to it by fording the Ara, and was presently satisfied I had entered one of the clefts I had contemplated from Mont Perdu. Its aperture is at the summit of Torla, which by my barometrical observations I found to be one thousand and eighty-one 5 м 2 * metres, or five hundred and fifty-six toises. I rambled in this cleft for four hours, : always under the shade of a thick stately forest, and inclosed between vertical walls of dreadful elevation. The day was drawing towards its close when we reached the extremity of the cleft; the platform was still above our heads, surrounded with those walls. so impossible to climb, which determined us to pass the night under the shelter of a rock overspread with tufts of the gonista lusitanica a very rare shrub, which we cut to light and feed our fire. We found the height of this station to be nine hundred and twenty-five toises. At the break of the following day we proceeded to reconnoitre the walls, which after two unsuccessful attempts and not without imminent danger, we scaled with our hands and feet. Having attained the platform, the face of every thing seemed changed around us, and in such a manner that we hardly knew where we were. Mont Perdu, the cylinder, its walls and clefts, were before us, but we were enabled to single them out from amidst the chaos of rocks so piled upon each other; it was necessary then I should traverse the platform to adjust my observations with those I had made on the summit. After more than once consulting the barometer on different situations of the platform, its mean elevation I found to be two thousand four hundred and thirty metres, or something more than one thousand two hundred toises. This height, compared with those I had taken at the bottom of the valley, gives an advantage over its upper extremity of five hundred and thirty-six metres, and is one thousand two hundred and fifty-seven metres above its mouth, so that the mean depth of the cleft will be eight hundred and ninety-six metres, or four hundred and fifty-nine toises. Having now ranged in two directions the meridional side of this shell-composed chain, I will in a few words give the result of my observations. With respect to the general disposition of the surface or ground, it is certain that the steeps are much more precipitous on the south than north; the mountains too sink faster, and the valleys are deeper, though at the same time this side of the chain has less transversal breadth than the other, and the surface of this part of Spain is higher than the corresponding surface of France. As to the nature of these mountains, they are all secondary; the last primitive materials I noticed were in the Port of Gavarnie: here at its utmost elevation we find granite, and we afterwards leave to the north limestone, and afterwards large very inclining shelves of grauwakke, alternating with flakes of grauwacken-schieffer, the latter is very much intermixed with wrecks of aquatic monocotyledones plants, whose forms are frequently spread with a pyritous varnish; it is, we know, in this species of rock that the most ancient remains of organised beings are to be met with, beyond all is composed in some sort, of two elements; gravel more or less coarse, and fetid limestone, more or less polluted with clay, both mixed in all proportions, from the pudding and the freestone, where the union is hardly discernible, to the compact limestone in which the sand is with dificulty recognised; but with this difference, that the beds wherein flint and sand predominate constitute the greatest portion of the mountains, and compact limestone is seldom found there but in small, irregular, and shelving beds; finally marine bodies are chiefly discovered in beds composed of sand of a moderate fineness, and in mean proportion, few are met with in freestone of gross quality, and fewer yet in marbles, and among the number of fossils, the species in which they most prevail is that of the lenticulares numismales, and here they are so abundant as to strike minds the most accustomed to the contemplation of the destruction of nature. I have met with them of three dimensions, and they appear to constitute as many distinct species; the diameter of the smallest rarely exceeds two millimetres, and is frequently much less; the first is found upon the summit of Mont Perdu, and appears to have suffered from transportation, and its exterior forms are greatly defaced; the second is found along the Val de Broto even to the deepest part of the Val d'Ordesa, it takes its residence in the inferior or lower beds, and discovers itself evidently enough by the tubercles on its surface, and internal spires: its diameter attains to about half an inch; the third is about an inch and a half in diameter, and is found in the lowest beds, below Torla, towards the plain. Further respecting the disposition of all their materials, it is too wonderful in the history of secondary mountains to be passed over, particularly the range of Marbore and Mont Perdu, the beds of which are arranged in such a manner as very frequently to take a vertical situation, and the most elevated summits of this mineralogical parallel are formed of beds thus disposed; but we scarcely find ourselves in the Val de Broto, when the beds become horizontal, without a possibility of discovering their relative positions, or where the change begins. The horizontal beds are very precipitous, like those which are vertical, and like them are vertically divided by fissures crossing from one side to the other. We might in more than one place be easily deceived, and take these trenches for beds, if we were not particular in noticing the order of the upper position of their materials. It is this disposition to divide itself vertically, however constructed its beds, which in a very eminent degree characterises the chain of Mont Perdu and all its dependances; and it arises from the spontaneous division of its beds into small solids, the form of which tends more or less to a rectangular parallelopiped, and there is even in the sand which incorporates itself in these beds, an apparent tendency to a similar division, which has been remarked frequently in the freestones of other parts of Europe. But what in other places would be considered a phenomenon of no magnitude, and comprehended by a very cursory view, takes here a character for grandeur so prodigious, that even the acknowledged proceedings of nature appear at first incompetent to the explanation of such uncommon forms. Further in no part were these forms so imposing as in those great clefts I had just explored. Their surface is a succession of steps perfectly horizontal, and formed by beds of freestone, with which we observed intermixed the red freestone, considered by geologists as the most ancient of the globe. Here the torrents are so regular in their fall, that the whole passage they make to themselves seems to be the work of man. The positions too of these immense fissures, disposed into stories of prodigious elevation, and on every side of us lost to our sight, their perpendicular materials, colour, and joinings, so much recal to our minds structures raised by the hand of man, that we imagine ourselves contemplating the ruins of some immense edifice. The pudding stone and freestone constitute the largest portion of these walls; but the compact limestone separates them here and there in large strata; upon the higher landings these are particularly observed in small beds, not difficult to be distinguished, and always horizontal in their position. The first beds I noticed upon the platform were yet horizontal, and are composed of a pudding stone, in which the flints and sand form in the calcareous sand very irregular undulating veins. But at the approach of the peak the position of the beds are entirely changed. At the base of Mont Perdu I found the shell-composed beds varying themselves to the south, and dipping to the north on an angle of 45° an inclination the very opposite to that of similar beds which constitute the northern base of the same peak. It is therefore certain that the beds of this mountain are, as it were, an open fan, the vertical rays of which constitute its summit; a very singular disposition, and an inversion of that which a rise. or burst* could have produced. It is further certain, that the beds arranged towards the peaks are precisely the shortest, the most irregular, and intertwined; and that there is a coherency and regularity in those beds very proportional to their approach to a perfect horizontal position. We cannot doubt that the latter are in their natural and original position, and that they owe their regularity to the soil upon which they have been deposited. Besides the waters by which they were collected being turbulent, have by turns thrown up calcareous slime, sands, and heavy flints, and mixed their various materials with an effort, the signs of which cannot be mistaken. I have already in another place attempted to establish the fact, that the course of these waters was rapidly impelled in a direction from the south-west to the north-east, and this is strongly here evinced by the position of the different masses and the situation of the steeps. The force then of these currents, upon the southern face of the primitive chain, would naturally lodge the matter they accumulated very irregularly upon its sides, not less on account of the inclination and ruggedness of the surface which received it, as by reason of the agitation, whirlpools, and swelling of the waves, by which it was impelled along. The irregular beds which these tumultuary impulsions occasioned, being at first unstably lodged upon very oblique planes, have removed from them, as soon as they had received a considerable addition to their bulk and weight; and it is natural to imagine that the most inclined of these beds must have fallen upon the regular deposits beneath, and that several of them have maintained an hold upon the lower trenches. A movement of this nature is more easily imagined than an eruption, the causes of which must be looked for in some vague hypothesis, and whose natural effect would be rather to lift up the beds in shifts, upon each other, than spread them out like a fan. In the mean time one of the greatest difficulties yet remains unaccounted for; it is not easy to comprehend how such masses, evidently as it were, turned upside down, have taken their stations several hundred metres above the summits of the mountains, from whence we might believe them to have been thrown down. Has it then arisen from the sinkings that have lowered, as there are many circumstances to induce a belief, the northern mountains? or have their summits been subjected to a more rapid waste, as other facts authorise us to imagine? Let us however confess, there is nothing clearly to be depended upon, excepting that some extraordinary convulsion of nature has subjected the higher beds of Mont Perdu to a change of position. Another circumstance is also clear, and that is, that this convulsion has originated beneath the waters, as is evident from those upper disposed shelves, on the summit of the overturned beds; which upper deposites may have occupied many vacuities, enlarged many ridges, and strongly cemented the crumbling masses with the compressed ones. The first vallies, the vestiges of which are sufficiently distinguishable, have been formed upon these mountains by the retiring of the waters, and these waters, having once found their natural level, have left these masses to disiccation, and their natural weight; the general or partial sinkings too of these masses, have occasioned the great southern clefts; and probably the deep vallies to the north and west, which divide by diverging, having always Mont Perdu for their centre. Doubtless these clefts have at first been no other than narrow fissures, and by degrees, since enlarged by the fall of their walls; the varied position of the beds to the north of Mont Perdu, and the diversity of the matter seated upon them, has determined irregularly this enlargement; and the vallies have expanded themselves from their bottoms to their edges in a multitude of different angles: to the south on the contrary, the tendency of the beds in every way vertically to divide themselves, never fails to leave behind their fallen surfaces perpendicular craggs; and the destruction acting always in the same manner, upon substances always similar, has increased the fissures by sections parallel to their first line, insomuch that their projecting and returning angles have every where retained their original correspondence. * Soulevement. I will not extend these reflections farther; what I have already said is sufficient for the singularities of one mountain; but this mountain is not only the highest of the Pyrenees, it is also the most elevated point of our hemisphere whereon organic wrecks have been discovered; it is, in a word, of all the known mountains, the last labours of the sea, in its volume the most considerable, and the most extraordinary from its structure. A ground like this is classical for the study of secondary mountains, and the history of the last revolutions of the globe. It will afford a reiterated exercise to the sagacity of the interpreters of nature; and, from what I have myself advanced regarding it, it will be evident I am very far from having exhausted its geology. > 1 END OF THE FOURTH VOLUME. |