Part 4 (1/2)
On Friday, the 17th of July, we commenced our measurements. Through the kindness of Sir Roderick Murchison, I found myself in the possession of an excellent five-inch theodolite, an instrument with the use of which both my friend Hirst and myself were perfectly familiar. We worked in concert for a few days to familiarize our a.s.sistant with the mode of proceeding, but afterwards it was my custom to simply determine the position where a measurement was to be made, and to leave the execution of it entirely to Mr. Hirst and our guide.
On the 20th of July I made a long excursion up the glacier, examining the moraines, the creva.s.ses, the structure, the moulins, and the disintegration of the surface. I was accompanied by a boy named Edouard Balmat,[A] and found him so good an iceman that I was induced to take him with me on the following day also.
[Sidenote: THE CLEFT STATION. 1857.]
Looking upwards from the Montanvert to the left of the Aiguille de Charmoz, a singular gap is observed in the rocky mountain wall, in the centre of which stands a detached column of granite. Both cleft and pillar are shown in the frontispiece, to the right. The eminence to the left of this gap is signalised by Professor Forbes as one of the best stations from which to view the Mer de Glace, and this point, which I shall refer to hereafter as the _Cleft Station_, it was now my desire to attain. From the Montanvert side a steep gully leads to the cleft; up this couloir we proposed to try the ascent. At a considerable height above the Mer de Glace, and closely hugging the base of the Aiguille de Charmoz, is the small Glacier de Tendue, shown in the frontispiece, and from which a steep slope stretches down to the Mer de Glace. This Tendue is the most _talkative_ glacier I have ever known; the clatter of the small stones which fall from it is incessant. Huge ma.s.ses of granite also frequently fall upon the glacier from the cliffs above it, and, being slowly borne downwards by the moving ice, are at length seen toppling above the terminal face of the glacier. The ice which supports them being gradually melted, they are at length undermined, and sent bounding down the slope with peal and rattle, according as the ma.s.ses among which they move are large or small. The s.p.a.ce beneath the glacier is c.u.mbered with blocks thus sent down; some of them of enormous size.
[Sidenote: ROUGH ASCENT. 1857.]
The danger arising from this intermittent cannonade, though in reality small, has caused the guides to swerve from the path which formerly led across the slope to the promontory of Trelaporte. I say ”small,”
because, even should a rock choose the precise moment at which a traveller is pa.s.sing to leap down, the boulders at hand are so large and so capable of bearing a shock that the least presence of mind would be sufficient to place him in safety. But presence of mind is not to be calculated on under such circ.u.mstances, and hence the guides were right to abandon the path.
Reaching the mouth of our gully after a rough ascent, we took to the snow, instead of climbing the adjacent rocks. It was moist and soft, in fact in a condition altogether favourable for the ”regelation” of its granules. As the foot pressed upon it the particles became cemented together. A portion of the pressure was transmitted laterally, which produced attachments beyond the boundary of the foot; thus as the latter sank, it pressed upon a surface which became continually wider and more rigid, and at length sufficiently strong to bear the entire weight of the body; the pressed snow formed in fact a virtual _camel's foot_, which soon placed a limit to the sinking. It is this same principle of regelation which enables men to cross snow bridges in safety. By gentle cautious pressure the loose granules of the substance are cemented into a continuous ma.s.s, all sudden shocks which might cause the frozen surfaces to snap asunder being avoided. In this way an arch of snow fifteen or twenty inches in thickness may be rendered so firm that a man will cross it, although it may span a chasm one hundred feet in depth.
As we ascended, the incline became very steep, and once or twice we diverged from the snow to the adjacent rocks; these were disintegrated, and the slightest disturbance was sufficient to bring them down; some fell, and from one of them I found it a little difficult to escape; for it grazed my leg, inflicting a slight wound as it pa.s.sed. Just before reaching the cleft at which we aimed, the snow for a short distance was exceedingly steep, but we surmounted it; and I sat for a time beside the granite pillar, pleased to find that I could permit my legs to dangle over a precipice without prejudice to my head.
[Sidenote: CHAMOIS ON THE MOUNTAINS. 1857.]
While we remained here a chamois made its appearance upon the rocks above us. Deeming itself too near, it climbed higher, and then turned round to watch us. It was soon joined by a second, and the two formed a very pretty picture: their att.i.tudes frequently changed, but they were always graceful; with head erect and horns curved back, a light limb thrown forward upon a ledge of rock, looking towards us with wild and earnest gaze, each seemed a type of freedom and agility. Turning now to the left, we attacked the granite tower, from which we purposed to scan the glacier, and were soon upon its top. My companion was greatly pleased--he was ”tres-content” to have reached the place--he felt a.s.sured that many old guides would have retreated from that ugly gully, with its s.h.i.+fting s.h.i.+ngle and debris, and his elation reached its climax in the declaration that, if I resolved to ascend Mont Blanc without a guide, he was willing to accompany me.
[Sidenote: SCENE FROM THE STATION. 1857.]
From the position which we had attained, the prospect was exceedingly fine, both of the glaciers and of the mountains. Beside us was the Aiguille de Charmoz, piercing with its spikes of granite the clear air.
To my mind it is one of the finest of the Aiguilles, n.o.ble in ma.s.s, with its summits singularly cleft and splintered. In some atmospheric colourings it has the exact appearance of a mountain of cast copper, and the manner in which some of its highest pinnacles are bent, suggesting the idea of ductility, gives strength to the illusion that the ma.s.s is metallic. At the opposite side of the glacier was the Aiguille Verte, with a cloud poised upon its point: it has long been the ambition of climbers to scale this peak, and on this day it was attempted by a young French count with a long retinue of guides. He had not fair play, for before we quitted our position we heard the rumble of thunder upon the mountain, which indicated the presence of a foe more terrible than the avalanches themselves. Higher to the right, and also at the opposite side of the glacier, rose the Aiguille du Moine; and beyond was the basin of the Talefre, the ice cascade issuing from which appeared, from our position, like the foam of a waterfall. Then came the Aiguille de Lechaud, the Pet.i.te Jora.s.se, the Grande Jora.s.se, and the Mont Tacul; all of which form a cradle for the Glacier de Lechaud. Mont Mallet, the Periades, and the Aiguille Noire, came next, and then the singular obelisk of the Aiguille du Geant, from which a serrated edge of cliff descends to the summit of the ”Col.”
[Sidenote: SeRACS OF THE COL DU GeANT. 1857.]
Over the slopes of the Col du Geant was spread a coverlet of s.h.i.+ning snow, at some places apparently as smooth as polished marble, at others broken so as to form precipices, on the pale blue faces of which the horizontal lines of bedding were beautifully drawn. As the eye approaches the line which stretches from the Rognon to the Aiguille Noire, the repose of the _neve_ becomes more and more disturbed. Vast chasms are formed, which however are still merely indicative of the trouble in advance. If the glacier were lifted off we should probably see that the line just referred to would lie along the summit of a steep gorge; over this summit the glacier is pushed, and has its back periodically broken, thus forming vast transverse ridges which follow each other in succession down the slope. At the summit these ridges are often cleft by fissures transverse to them, thus forming detached towers of ice of the most picturesque and imposing character.[B] These towers often fall; and while some are caught upon the platforms of the cascade, others struggle with the slow energy of a behemoth through the debris which opposes them, reach the edges of the precipices which rise in succession along the fall, leap over, and, amid ice-smoke and thunder-peals, fight their way downwards.
[Sidenote: GLACIER MOTION. 1857.]
A great number of secondary glaciers were in sight hanging on the steep slopes of the mountains, and from them streams sped downwards, falling over the rocks, and filling the valley with a low rich music. In front of me, for example, was the Glacier du Moine, and I could not help feeling as I looked at it, that the arguments drawn from the deportment of such glaciers against the ”sliding theory,” and which are still repeated in works upon the Alps, militate just as strongly against the ”viscous theory.” ”How,” demands the antagonist of the sliding theory, ”can a secondary glacier exist upon so steep a slope? why does it not slide down as an avalanche?” ”But how,” the person addressed may retort, ”can a ma.s.s which you a.s.sume to be viscous exist under similar conditions? If it be viscous, what prevents it from rolling down?” The sliding theory a.s.sumes the lubrication of the bed of the glacier, but on this cold height the quant.i.ty melted is too small to lubricate the bed, and hence the slow motion of these glaciers. Thus a sliding-theory man might reason, and, if the external deportment of secondary glaciers were to decide the question, De Saussure might perhaps have the best of the argument.
And with regard to the current idea, originated by M. de Charpentier, and adopted by Professor Forbes, that if a glacier slides it must slide as an avalanche, it may be simply retorted that, in part, _it does so_; but if it be a.s.serted that an _accelerated motion_ is the necessary motion of an avalanche, the statement needs qualification. An avalanche on pa.s.sing through a rough couloir soon attains a uniform velocity--its motion being accelerated only up to the point when the sum of the resistances acting upon it is equal to the force drawing it downwards.
These resistances are furnished by the numberless asperities which the ma.s.s encounters, and which incessantly check its descent, and render an acc.u.mulation of motion impossible. The motion of a man walking down stairs may be on the whole uniform, but it is really made up of an aggregate of small motions, each of which is accelerated; and it is easy to conceive how a glacier moving over an uneven bed, when released from one opposing obstacle will be checked by another, and its motion thus rendered sensibly uniform.
[Sidenote: MORAINES. 1857.]
[Sidenote: TRIBUTARIES OF THE MER DE GLACE. 1857.]
[Ill.u.s.tration: Fig. 7. Tributaries of the Mer de Glace.]
From the Aiguille du Geant and Les Periades a glacier descended, which was separated by the promontory of La Noire from the glacier proceeding from the Col du Geant. A small moraine was formed between them, which is marked _a_ upon the diagram, Fig. 7. The great ma.s.s of the glacier descending from the Col du Geant came next, and this was bounded on the side nearest to Trelaporte by a small moraine _b_, the origin of which I could not see, its upper portion being shut out by a mountain promontory. Between the moraine _b_ and the actual side of the valley was another little glacier, derived from some of the lateral tributaries. It was, however, between the moraines _a_ and _b_ that the great ma.s.s of the Glacier du Geant really lay. At the promontory of the Tacul the lateral moraines of the Glacier des Periades and of the Glacier de Lechaud united to form the medial moraine _c_ of the Mer de Glace. Carrying the eye across the Lechaud, we had the moraine _d_ formed by the union of the lateral moraines of the Lechaud and Talefre; further to the left was the moraine _e_, which came from the Jardin, and beyond it was the second lateral moraine of the Talefre. The Mer de Glace is formed by the confluence of the whole of the glaciers here named; being forced at Trelaporte through a pa.s.sage, the width of which appears considerably less than that of the single tributary, the Glacier du Geant.
In the ice near Trelaporte the blue veins of the glacier are beautifully shown; but they vary in distinctness according to the manner in which they are looked at. When regarded obliquely their colour is not so p.r.o.nounced as when the vision plunges deeply into them. The weathered ice of the surface near Trelaporte could be cloven with great facility; I could with ease obtain plates of it a quarter of an inch thick, and possessing two square feet of surface. On the 28th of July I followed the veins several times from side to side across the Geant portion of the Mer de Glace; starting from one side, and walking along the veins, my route was directed obliquely downwards towards the axis of the tributary. At the axis I was forced to turn, in order to keep along the veins, and now ascended along a line which formed nearly the same angle with the axis at the other side. Thus the veins led me as it were along the two sides of a triangle, the vertex of which was near the centre of the glacier. The vertex was, however, in reality rounded off, and the figure rather resembled a hyperbola, which tended to coincidence with its asymptotes. This observation corroborates those of Professor Forbes with regard to the position of the veins, and, like him, I found that at the centre the veining, whose normal direction would be transverse to the glacier, was contorted and confused.