The terminal moraine is about 500 feet high, quite barren, and thrown obliquely across the valley, from north-east to south-west, completely hiding the glacier. From its top successive smaller parallel ridges (indicating the periodic retirements of the glacier) lead down to the ice, which must have sunk several hundred feet. This glacier descends from Kinchinjhow, the huge cliff of whose eastern extremity dips into it. The surface, less than half a mile wide, is exceedingly undulated, and covered with large pools of water, ninety feet deep, and beds of snow, and is deeply corroded; gigantic blocks are perched on pinnacles of ice on its surface, and the gravel cones* [For a description of this curious phenomenon, which has been illustrated by Agassiz, see "Forbes's Alps," p. 26 and 347.] are often twenty feet high. The crevassing so conspicuous on the Swiss glaciers is not so regular on this, and the surface appears more like a troubled ocean; due, no doubt, to the copious rain and snow-falls throughout the summer, and the corroding power of wet fogs. The substance of the ice is ribboned, dirt-bands are seen from above to form long loops on some parts, and the lateral moraines, like the terminal, are high above the surface. These notes, made previous to reading Professor Forbes's travels in the Alps, sufficiently show that perpetual snow, whether as ice or glacier, obeys the same laws in India as in Europe; and I have no remarks to offer on the structure of glaciers, that are not well illustrated and explained in the abovementioned admirable work.
Its average slope for a mile above the terminal moraines was less than 5 degrees, and the height of its surface above the sea 16,500 feet by boiling-point; the thickness of its ice probably 400 feet. Between the moraine and the west flank of the valley is a large lake, with terraced banks, whose bottom (covered with fine felspathic silt) is several hundred feet above that of the valley; it is half a mile long, and a quarter broad, and fed partly by glaciers of the second order on Chango-khang and Sebolah, and partly by filtration through the lateral moraine.
Illustration—GNEISS-BLOCK WITH GRANITE BANDS, ON THE KINCHINJHOW
GLACIER.
CHAPTER XXIII.
Donkia glaciers — Moraines — Dome of ice — Honey-combed surface —
Rocks of Donkia — Metamorphic action of granite veins — Accident to
instruments — Sebolah pass — Bees, and May-flies — View —
Temperature — Pulses of party — Lamas and travellers at Momay —
Weather and climate — Dr. Campbell leaves Dorjiling for Sikkim —
Leave Momay — Yeumtong — Lachoong — Retardation of vegetation at
low elevations — Choongtam — Landslips and debacle — Meet Dr.
Campbell — Motives for his journey — Second visit to Lachen valley
— Autumnal tints — Red currants — Lachen Phipun — Tungu —
Scenery — Animals — Poisonous rhododendrons — Fire-wood — Palung
— Elevations — Sitong — Kongra Lama — Tibetans — Enter Tibet —
Desolate scenery — Plants — Animals — Geology — Cholamoo lakes —
Antelopes — Return to Yeumtso — Dr. Campbell lost — Extreme cold
— Headaches — Tibetan Dingpun and guard — Arms and accoutrements
— Temperature of Yeumtso — Migratory birds — Visit of Dingpun —
Yeumtso lakes.
On the 20th of September I ascended to the great Donkia glaciers, east of Momay; the valley is much longer than that leading to the Kinchinjhow glacier, and at 16,000 or 17,000 feet elevation, containing four marshes or lakes, alternating with as many transverse moraines that have dammed the river. These moraines seem in some cases to have been deposited where rocks in the bed of the valley obstructed the downward progress of the ancient glacier; hence, when this latter finally retired, it rested at these obstructions, and accumulated there great deposits, which do not cross the valley, but project from each side obliquely into it. The rocks in situ on the floor of the valley are all moutonneed and polished on the top, sides, and face looking up the valley, but are rugged on that looking down it: gigantic blocks are poised on some. The lowest of the ancient moraines completely crosses the river, which finds, its way between the boulders.
Under the red cliff of Forked Donkia the valley becomes very broad, bare, and gravelly, with a confusion of moraines, and turns more northwards. At the angle, the present terminal moraine rises like a mountain (I assumed it to be about 800 feet high),* [This is the largest and longest terminal moraine backed by an existing glacier that I examined with care: I doubt its being so high as the moraine of the Allalein glacier below the Mat-maark sea in the Sachs valley (Valais, Switzerland); but it is impossible to compare such objects from memory: the Donkia one was much the most uniform in height.] and crosses the valley from N.N.E. to S.S.W. From the summit, which rises above the level of the glacier, and from which I assume its present retirement, a most striking scene opened. The ice filling an immense basin, several miles broad and long, formed a low dome,* [This convexity of the ice is particularly alluded to by Forbes ("Travels in the Alps," p.386), as the "renflement" of Rendu and "surface bombee" of Agassiz, and is attributed to the effects of hydrostatic pressure tending to press the lower layers of ice upwards to the surface. My own impression at the time was, that the convexity of the surface of the Donkia glacier was due to a subjacent mountain spur running south from Donkia itself. I know, however, far too little of the topography of this glacier to advance such a conjecture with any confidence. In this case, as in all similar ones, broad expanses being covered to an enormous depth with ice, the surface of the latter must in some degree be modified by the ridges and valleys it conceals. The typical "surface bombee," which is conspicuous in the Himalaya glaciers, I was wont (in my ignorance of the mechanical laws of glaciers) to attribute to the more rapid melting of the edges of the glacier by the radiated heat of its lateral moraines and of the flanks of the valley that it occupies.] with Forked Donkia on the west, and a serried range of rusty-red scarped mountains, 20,000 feet high on the north and east, separating large tributary glaciers. Other still loftier tops of Donkia appeared behind these, upwards of 22,000 feet high, but I could not recognise the true summit (23,176 feet). The surface was very rugged, and so deeply honey-combed that the foot often sank from six to eight inches in crisp wet ice. I proceeded a mile on it, with much more difficulty than on any Swiss glacier: this was owing to the elevation, and the corrosion of the surface into pits and pools of water; the crevasses being but few and distant. I saw no dirt-bands on looking down upon it from a point I attained under the red cliff of Forked Donkia, at an elevation of 18,307 feet by barometer, and 18,597 by boiling-point. The weather was very cold, the thermometer fell from 41 degrees to 34 degrees, and it snowed heavily after 3 p.m.
The strike of all the rocks (gneiss with granite veins) seemed to be north-east, and dip north-west 30 degrees. Such also were the strike and dip on another spur from Donkia, north of this, which I ascended to 19,000 feet, on the 26th of September: it abutted on the scarped precipices, 3000 feet high, of that mountain. I had been attracted to the spot by its bright orange-red colour, which I found to be caused by peroxide of iron. The highly crystalline nature of the rocks, at these great elevations, is due to the action of veins of fine-grained granite, which sometimes alter the gneiss to such an extent that it appears as if fused into a fine granite, with distinct crystals of quartz and felspar; the most quartzy layers are then roughly crystallized into prisms, or their particles are aggregated into spheres composed of concentric layers of radiating crystals, as is often seen in agates. The rearrangement of the mineral constituents by heat goes on here just as in trap, cavities filled with crystals being formed in rocks exposed to great heat and pressure. Where mica abounds, it becomes black and metallic; and the aluminous matter is crystallised in the form of garnets.
Illustration—SUMMIT OF FORKED DONKIA, AND "GOA" ANTELOPES.
At these great heights the weather was never fine for more than an hour at a time, and a driving sleet followed by thick snow drove me down on both these occasions. Another time I ascended a third spur from this great mountain, and was overtaken by a heavy gale and thunderstorm, the latter is a rare phenomenon: it blew down my tripod and instruments which I had thought securely Propped with stones, and the thermometers were broken, but fortunately not the barometer. On picking up the latter, which lay with its top down the hill, a large bubble of air appeared, which I passed up and down the tube, and then allowed to escape; when I heard a rattling of broken glass in the cistern. Having another barometer* [This barometer (one of Newman's portable instruments) I have now at Kew: it was compared with the Royal Society's standard before leaving England; and varied according to comparisons made with the Calcutta standard 0.012 during its travels; on leaving Calcutta its error was 0; and on arriving in England, by the standard of the Royal Society, +.004. I have given in the Appendix some remarks on the use of these barometers, which (though they have obvious defects), are less liable to derangement, far more portable, and stand much heavier shocks than those of any other construction with which I am familiar.] at my tent, I hastened to ascertain by comparison whether the instrument which had travelled with me from England, and taken so many thousand observations, was seriously damaged: to my delight an error of 0.020 was all I could detect at Momay and all other lower stations. On my return to Dorjiling in December, I took it to pieces, and found the lower part of the bulb of the attached thermometer broken off, and floating on the mercury. Having quite expected this, I always checked the observations of the attached thermometer by another, but—how, it is not easy to say—the broken one invariably gave a correct temperature.