Western Himalaya and Tibet Part 31

Wherever I have seen glaciers in Tibet or the mountains of India, I have been able to trace their moraines to a level very considerably lower than their present termination; and when I find in those ranges of the Himalaya which do not at present attain a sufficient elevation to be covered with perpetual snow, series of angular blocks, evidently transported, because different from the rocks which occur _in situ_, and, so far as I can judge, exactly a.n.a.logous in position to the moraines of present glaciers, I feel myself warranted in concluding that they are of glacial origin, and find it necessary to look about for causes which should render it probable that the snow-level should have formerly been lower than it is at present. In the rainy districts of the Himalaya, where forest covers the slopes of the hills, it is difficult to fix the lowest limits at which evident moraines occur, but in many places I have seen them at least three thousand feet lower than the terminations of the present glaciers. In the valley of the Indus, acc.u.mulations of boulders, which I believe to be moraines, occur in Rondu as low as 6000 feet.

Glaciers, as is well known, terminate inferiorly at the point where the waste by melting in any given time begins to exceed in amount the ma.s.s of solid ice which is in the same s.p.a.ce of time pushed forward by the _vis a tergo_. In the mountains of Tibet the elevation of this point is very different in different places. It seems to depend princ.i.p.ally on the ma.s.s of the glacier, as large glaciers invariably descend much lower than those of smaller size; the inclination of the bed has perhaps also some influence in determining the matter.

In comparing the glaciers of the Tibetan Himalaya with those on the Indian face of the same mountains, it will be found that, _caeteris paribus_, glaciers descend much lower on the Indian side, or in a moist climate, than in the dry and arid Tibetan climate. It is indeed impossible to ascertain with certainty that any two glaciers are of equal size, but it appears to me sufficiently accurate to compare the main glaciers on the opposite sides of the same pa.s.s. In the Umasi pa.s.s, which is situated in the main chain of the trans-Sutlej Himalaya, all the circ.u.mstances seem favourable for comparison. On the south side of this pa.s.s the princ.i.p.al glacier terminates at about 11,500 feet, while on the north side a much more ma.s.sive glacier comes to an end abruptly at 14,000 feet. The difference then, on opposite sides of the same pa.s.s, where the pa.s.s coincides with the line of transition of climate, amounts to 2500 feet.

That I am justified in ascribing the cause of this difference to the change of climate appears from the fact, that in the interior of Tibet, where no such change is observed in crossing even very lofty pa.s.ses, there is frequently a glacier on the north declivity when none exists on the south. This is the case, for instance, on the Parang pa.s.s, and on the pa.s.s immediately north of Le. It may therefore be inferred, that when glaciers occur on both sides of a pa.s.s, that on the northern exposure will, unless there be a marked alteration of climate, invariably descend lower than that on the south side. I have not had an opportunity of seeing glaciers on both sides of any pa.s.s in the most external ranges of the Himalaya, but I have been informed that in the range south of the Chenab river, glaciers frequently occur on the north sides of the pa.s.ses, while none exist towards the south.

If this were to be found universally the case, it would be an additional proof that the lower descent of glaciers on the south or Indian side of the mountain chain is an exceptional occurrence.

[Sidenote: GLACIERS OF KOUENLUN.]

The glaciers of the southern slope of the Kouenlun appear, from the descriptions of travellers, to be on a still more gigantic scale than those of the Himalaya. Five mountain ranges of great height, separated from one another by rivers of great size, descend from the axis of that chain towards the Indus and Shayuk, and attain so great an elevation, that, with scarcely an exception, there is no pa.s.sage from one of these lateral valleys to another. All these ranges rise far above the line of perpetual snow, and in their valleys enormous glaciers descend to a level which is gradually lower as we advance westward in the direction of the source of the rain- and snow-fall.

The range east of the Shayuk has comparatively few and small glaciers, but to the west of that river the glaciers of Sa.s.sar terminate at about 15,000 feet. A little further west, a glacier, overhanging the valley of Nubra, terminates at 14,700 feet, and the great glacier of Nubra was found, by Captain Strachey, to terminate at 13,000 feet. In the range between Nubra and the Machulu again there are vast glaciers, but their height has not been determined, nor do we know precisely to what level those of the Shigar valley descend; though it is evident, from their proximity to the main valley, and their small distance from Shigar, which is not more than 7200 feet above the level of the sea, that they must descend very low, perhaps to 10,000 feet. In the valley of Gilgit, I am informed by Mr. Winterbottom, the glaciers descend as low as 8000 feet.

[Sidenote: LEVEL OF PERPETUAL SNOW.]

In the mountains further east than the Shayuk it would appear that the snow-fall is so very small that the level of perpetual snow recedes to an enormous height. This has been found to be the case on the pa.s.ses north of the Pangong lake, many of which were crossed by Captain H.

Strachey. The great height of the mountains without snow, east of the Karakoram pa.s.s, confirms the fact; and it is probable, so rapidly does the snow-level rise in advancing eastward, that if we could penetrate a very short distance beyond the eastern extremity of the Pangong lake, an absolutely dry country might be reached, in which rain or snow never falls.

So much error has unfortunately taken place regarding the height above which the mountains of North-west India are covered with perpetual snow, that it appears necessary that travellers should put upon record the results of their observations, however limited. It is for this reason, and not because I expect to throw much additional light on the subject, that the following remarks are hazarded. The recent paper of Captain R. Strachey[39] has furnished facts which had hitherto been wanting, while the theoretical considerations which have been laid down by Humboldt are so accurate and comprehensive, that the undoubted mistake into which he has fallen is the more to be regretted.

The Indian and Tibetan Himalaya, west of Nipal, lies entirely within the temperate zone, and from that circ.u.mstance has its year divided into summer and winter. The periodical rains, which it is well known are princ.i.p.ally confined to the outermost parts of the mountains, being derived from the Bay of Bengal, are excessive in the easternmost part of the chain, and gradually diminish as we advance westward; there is no reason, however, to believe that the winter monsoon, which is particularly dwelt upon by Captain Strachey in the valuable paper to which I have had occasion to refer, is so. Probably indeed it is the reverse, though I have no detailed observations to refer to in corroboration of this opinion; I may however recall to mind, that the winter is the season of heavy snow, and the spring of heavy rain, throughout the north of Affghanistan, and that in the Punjab frequent cloudy weather and rain occurs during the cold season, while in the plains of India the weather seems to become at that period less unsettled as we advance eastward.

The quant.i.ty of rain which falls during the summer in the outer Himalaya has necessarily a very material influence on the sun's action during the time in which he has most power, and therefore on the mean temperature of the summer months, which at corresponding elevations, notwithstanding the northing of the chain as we advance from east to west, must be higher to the westward. In the interior or Tibetan portion of the Himalaya, this difference is not observed, the climate being the same, or nearly so, from east to west of the region under consideration.

[Sidenote: WINTER, THE SEASON OF SNOW.]

In the most western part of the Himalaya, in Kashmir and Balti, the winter's fall of snow commences about the beginning of December, and continues on the highest ranges nearly to the beginning of May. The supply of moisture from which the snow is condensed is evidently derived from the Indian seas, and I suppose princ.i.p.ally from the south-west, that being the general direction from which I observed snow-storms to arrive at Iskardo. The fall of snow must therefore, equally with that of rain in the rainy season, be greatest in the outermost (snowy) ranges, and very much less in all those in the interior. In the lower parts of Tibet on the Indus the snow-fall during winter is very considerable, though during summer the climate is as dry as elsewhere in Tibet. This difference seems to be explained by the westerly point from which the winter's wind blows, and by the much greater moisture of the atmosphere at that season over Affghanistan and Sind, so that the south-west wind advances loaded with vapour up the valley of the Indus. The increase of elevation in the bed of that river of course causes all the excess of moisture to be deposited without penetrating to any great distance, so that the more eastern parts of the country are not affected by this cause.

The snowy season in the highest mountains is probably in every part of the range very much the same. On the low outer ranges, which do not attain the height of perpetual snow, it is gradually lessened in duration as the elevation diminishes, ceasing entirely, in average years, at about 4000 feet. When the winter is at an end, the influence of a powerful sun and gradually increasing temperature is at once brought to bear on the ma.s.s of snow which has fallen; on the inner ranges where the summer is dry, this action proceeds uninterruptedly till the commencement of the next winter, but on the outermost snowy ranges it is modified by the access of the rainy season.

[Sidenote: MELTING OF SNOW IN SUMMER.]

On the outer ranges of the Himalaya, the crests of which rise to between five and ten thousand feet, the powerful sun soon dissipates all snow. It is in the inner ranges, which rise nearly to the height of perpetual snow, and where the river-beds are from six to eight thousand feet above the level of the sea, that the snow remains for a great length of time. When the valleys are open, the plain on the banks of the stream becomes first of all bare of snow, then the banks which face the south, and lastly the northern slopes. It is not so, however, in the deep narrow valleys and ravines through which the Himalayan rivers generally flow. In these the bottom of the glen is so much sheltered from the sun that a dense ma.s.s of snow, the result of acc.u.mulation from the avalanches of the winter, remains for a very long time after both slopes are quite bare of snow. These _snow-beds_ have nothing of the nature of a glacier in them, but are simply firm, hard snow. I have, in the month of June, descended along one of them from 13,000 feet (above which height there was perhaps a glacier beneath), to 8500 feet, a distance of seven miles without a break. It was entirely confined to the bottom of the ravine, both banks being throughout all that distance free of snow, and often covered with a most luxuriant herbage.

[Sidenote: SNOW-BEDS IN RAVINES.]

Similar snow-beds are to be seen in every ravine which is not too wide to be choked up by snow in winter. Their occurrence so universally is probably in a great measure the reason why glaciers were not recognized in our Indian mountains till so recent a period. These beds being so clearly transitory in existence, it was a.s.sumed that all ma.s.ses of snow and ice were equally so. A visit to one of the great glaciers at the end of autumn would of course at once have indicated the dissimilarity.

In many narrow ravines remains of these snow-beds may be seen at surprisingly low elevations throughout the year, their permanence depending much more on the amount of the winter's fall of snow, and of the acc.u.mulation in that particular locality, than upon the mean or summer temperature of the place. At Baltal, in the upper part of the Sind valley in Kashmir, the little stream which descends from the Zoji pa.s.s was still arched over by a bed of snow several feet thick, in the end of September, at an elevation of not more than 9500 feet. This was not, as might have been expected, in a very shady spot, but fully exposed to the action of the sun; it was, however, in a place where the fall of snow during winter is very great.

The causes which are enumerated by Baron Humboldt as affecting the snow-level are numerous, but several are of only local effect. Two in addition to the lat.i.tude seem more important than the others, namely, the amount of fall during winter, and the amount of solar heat during summer. Captain R. Strachey regards the diminished amount of the winter's fall of snow as the main cause of the greater height of the snow-line in the interior of the Himalaya, but I feel disposed to believe that both causes co-operate equally to produce the effect.

[Sidenote: LEVEL OF PERPETUAL SNOW.]

Captain R. Strachey has estimated (from the mean of several observations) the snow-level on the southern slope of the cis-Sutlej Himalaya at 15,500 feet. This elevation is, no doubt, as near as possible correct. Captain Herbert, in his geological report, had fixed upon 15,000 feet, which is a little too low even in the district of Basehir, to which his estimate, I believe, refers. In the trans-Sutlej Himalaya, from the diminished amount of summer cloudy weather, the snow-level is probably a little higher, but we are not yet in possession of any accurate determinations of heights in that range in those parts which are in close contact with the plains of India. Two of its ramifications are extremely well adapted for determining the height of perpetual snow. First, the Chumba range, which, as has been pointed out to me by Major Cunningham, is barely snow-tipped throughout the year; and second, the Pir Panjal range south of Kashmir, the northern slopes of which have perpetual snow and glaciers, while on the south side the snow has entirely melted before the end of summer. The elevation of the Pir Panjal has not been determined with accuracy, the heights given by Baron Hugel and by Mr.

Vigne being estimated from their measurement of the pa.s.s over which they crossed[40].

[Sidenote: SNOW-LEVEL IN TIBET.]

In the interior of north-west Tibet every princ.i.p.al range attains the elevation of perpetual snow, but only a few peaks rise much above it.

There is therefore no very great ma.s.s of snow during the summer months to lower the temperature of the air, and consequently circ.u.mstances are the most favourable possible for the elevation of the snow-line to an extreme degree; a dry, stony, desert, treeless country, violent winds, clear sky, and powerful sun, being all combined. In the most central part of the country, the Lanak pa.s.s, near Hanle, and the Sabu pa.s.s, near Le, both elevated as nearly as possible 18,000 feet, are without perpetual snow, but the Parang pa.s.s, between 18,400 and 18,600 feet, has a glacier on its north face, and therefore exceeds in elevation the snow-line. The snow-level in central Tibet must therefore be sought between these heights, but nearer that of the Parang pa.s.s, which has no perpetual snow towards the south: it is, therefore, certainly not below 18,000 feet.

In the Kouenlun, on the northern border of Tibet, where the mountains are again much more elevated, the snow-level descends no lower. Even on the 19th and 20th of August, the ma.s.s of snow, which was on the northern face of its highest peaks continuous down from 20,000 feet and upwards, did not descend below 17,500 feet, and the open level plain of the upper Shayuk had at that height only trifling patches of snow. On the Karakoram pa.s.s (18,200 feet) there were only large patches of snow, the south face of the ridge being quite bare for some distance in both directions.

[Sidenote: LEVEL ON OPPOSITE SIDES OF Pa.s.sES.]

The _vexata quaestio_ of the difference of the level at which snow lies on the north and south slopes of the Himalaya, affords a singular instance of misconception. Enunciated originally in an obscure and somewhat incorrect form, when little was known of the structure of the inner part of the chain, the fact has been repeatedly contradicted by those who thought they found it contrary to their experience. Both parties were to a certain extent right. On each individual range the snow-level will at all times be found lower on the north face than on the south, except when the range which we are crossing happens to coincide with a very marked and abrupt change of climate, which will only be the case when it is extremely elevated. When this is the case, the proposition, otherwise true of the mountains _en ma.s.se_, or the inner ranges compared with the outer, becomes applicable to a particular range. This is probably the case in the very pa.s.s in Kamaon (I know not which it was) from which the law was first inferred. It is certainly so in the great pa.s.ses north of the Chenab, where, on the Indian face, I found in June snow at 11,500 feet, while on the north side, only twenty miles distant, it had already receded beyond 15,000 feet.

From the rapid nature of my journey, and the great number of objects to which I was obliged to devote my attention, the geological observations which I was enabled to make were much more imperfect than I could have wished. It appeared, however, desirable, hurried as they were, to enumerate them, for the purpose of drawing the attention of future travellers to the subject; and for the same reason I shall here recapitulate the general conclusions which appear to result from the facts observed.

[Sidenote: GEOLOGY OF TIBET.]

The greater part of Tibet consists of plutonic and metamorphic rocks; and from the gigantic scale on which the sections are exposed, and the general bareness of the mountains, which enables their structure to be seen, that country probably presents the finest field in which these cla.s.ses of rocks could be studied. Granite occurs in great abundance, sending immense veins in all directions into the metamorphic rocks, which are seen to be everywhere upheaved and dislocated by the injected ma.s.s. In the immediate vicinity of the plutonic ma.s.ses, all traces of the direction of the strata of the superposed rocks are lost; but elsewhere, with every variety of dip, it is very generally found that the stratified rocks strike in a direction which varies between north-west and south-east, and north-north-west and south-south-east. As all my observations were made roughly and unconnectedly, and without my discovering this ident.i.ty till after my return to India, the strike is probably very uniform throughout a great extent of country.

It is not a little remarkable that a belt twenty miles wide, in the direction of this line of strike, drawn from Iskardo to the Niti pa.s.s, would cover every place south of the Indus in which limestone has been observed in Tibet. It would pa.s.s through Molbil on the Pashkyum river, the limestone districts of Zanskar, and the Lachalang pa.s.s, where limestone was found by Gerard. It would also cover Piti, Hangarang, and Bekhar, all well-known limestone tracts. Of course the limestones of Nubra and the Karakoram on the one hand, and of Kashmir on the other, cannot in any way be connected with this line.

The sandstones, slates, and conglomerates, which so closely resemble in appearance those rocks which in Europe are chiefly members of the old red sandstone and greywacke series, appear to a.s.sume also the same direction. I bring forward these coincidences of direction only as a remarkable fact, worthy of investigation, without attaching any great weight to them, as more careful observation may show that they are merely accidental, and that rocks of very different ages exist among the limestones and a.s.sociated rocks of the northern Himalaya.

[Sidenote: ALLUVIAL AND LACUSTRINE DEPOSIT.]

The great extent and development of a very modern alluvium-like formation, composed of great ma.s.ses of clay with boulders, and occasionally of very fine laminated clay, const.i.tutes one of the most remarkable and striking features of Western Tibet. In every part through which I have travelled, and at all elevations, except on the highest pa.s.ses, I have found these deposits in greater or less quant.i.ty. In their most common state they consist of loose earthy or clayey unstratified ma.s.ses, containing boulders either angular or rounded. Very fine clay, distinctly and horizontally stratified, is also common; sandstone and hardened conglomerate are more rare, but also occur occasionally.

That some of these beds are of lacustrine origin, the occurrence of fresh-water sh.e.l.ls appears to prove very clearly; and though here and there small portions may be terrestrial and of glacial origin, it cannot, I think, be doubted that the great ma.s.s of the boulder clay was deposited under water.

In the structure of Scotland at the present day we have a state of circ.u.mstances which appears to me capable of throwing much light on the nature of these deposits. We find there a series of narrow arms of the sea, stretching far into the land, and separated by rugged and generally steep ranges of metamorphic or plutonic rocks. They are all more or less silted up by sedimentary matter, and near their mouths, especially where, as is often the case, they are much contracted, we generally find a bar, shallower than the remainder. At various elevations above the sea-level again there is a series of fresh-water lakes, differing little in aspect from the arms of the sea. We find also in many parts of the Highlands of Scotland long valleys, nearly level, which are filled with incoherent sedimentary deposits, and bounded like the lochs by steep mountains. If these were formerly arms of the sea, which by the elevation of the land have been converted into dry land, then the fresh-water lakes probably occupy those parts of the narrow channels which were originally deepest, or which, being wider than the rest, have remained unoccupied by sedimentary matter at the time of the elevation. In conformity with this view we find that at the lower end of these lakes the mountains generally approach very close to one another.

If we were to suppose the gradual elevation of Scotland to continue till the mountains attained an elevation equal to that of the Himalaya, it is evident that a continued series of marine sedimentary deposits would extend from the summit to the sea-level, unless removed by the action of streams or other ordinary causes. Some of the valleys would be of considerable width, and would contain marine fossils in great abundance; but in the narrower mountain valleys the gravel and boulders would be quite dest.i.tute of fossils. Here and there fresh-water formations of partial extent would occur, but they would be separated from one another by large tracts filled with marine beds. The gradual elevation of the land would bring to bear upon these incoherent strata the powerful action of running water, which would remove portion after portion, till at last deep valleys would be excavated, and small patches only of the gravel and clay would remain where the action of the streams was least powerful. Such I conceive to be the present state of Tibet, but a much more detailed investigation of that remarkable country would be necessary, before this view can be regarded in any other light than an hypothesis.

The causes by which the metamorphic rocks, which must have been brought into their present remarkable state at a great depth in the interior of the globe, acquired their present configuration of mountain and valley, form a question on which I am not now prepared to enter. One continued process of elevation seems inadequate to produce the observed effects; but however numerous the alternations of elevation and depression may have been, it is evident that the alluvial deposits at present existing must all be referable to the last period of elevation, as such incoherent strata could not withstand the continued action of the sea.

FOOTNOTES:

[28] Asie Centrale, vol. i. p. 14.

[29] Manasarawar and Rawan Rhad.

[30] Moorcroft's Travels, vol. ii. pp. 47-50.

[31] Journal of the Asiatic Society of Calcutta, 1842, No. 126.

Captain Herbert, who had travelled a great deal in the Himalaya, was the first to point out the impropriety of regarding these mountains as a single chain parallel to the plains of India. Jacquemont also arrived at the same conclusion, as will be seen from the following extract from his journal:--"Le langage de la geographie descriptive est theorique; c'est une grande faute si les theories qu'il rappelle sans cesse sont denuees de fondement. Ainsi l'on dit que le Setludje _coupe_ la chaine centrale de l'Himalaya, que sa vallee est creusee au travers, etc., etc., et l'on donne a penser par la que cette chaine auparavant etait continue et que c'est par un effort des eaux que s'y est faite cette large trouee, comme si les montagnes avaient d se former primitivement avec une continuite non interrompue" (vol. ii. p.

201); and again (at p. 269), "Le Setludje coule donc non au nord de l'Himalaya, mais entre deux chaines a peu pres egalement elevees."

[32] Captain R. Strachey, in his paper on the snow-level, proposes to call the more western part of the Cis-Sutlej Himalaya the Busehir range, a name which, though exceedingly appropriate to the portion to which he applies it, is not adapted for extension to the more eastern part.

[33] Travels in Kashmir, etc., vol. ii. p. 382.

[34] Travels, vol. i. p. 361.

[35] That Tibet is not an extensive plain, according to the usual idea, has already been pointed out by Humboldt (Asie Centrale, vol. i.