NOTES ON THE WESTERNMOST PLATEAUX OF TIBET*

(Maps at the end of volume.)

DR. EMIL TRINKLER.

DURING the expedition I undertook in 1927-28 I twice crossed the high mountains separating the upper Indus valley from the Tarim, Basin of Chinese Turkistan. As the ranges were crossed on two different lines we were able to study two different sections right across this part of Central Asia. This was very important for the geologist of my party, Dr. Hellmut de Terra, who consequently formed a good idea of the geological history of this part of our globe.

The main aim of my own researches was to investigate the former glaciation of these regions during the Ice-Age. Professor Dainelli, the geologist of De Filippi's Karakoram expedition, has proved that there was at one time extensive glaciation of the regions of the upper Indus valley and Baltistanf and the question that interested me was whether the westernmost Tibetan plateaux and the Kun-lun mountains had also been covered by ice and snow.

My expedition started from Leh, crossed the Chang La on the 16th July 1927, spent some days on the western shore of the Pangong Lake and arrived at Phobrang on the 28th July. This route has been described before, so I need say little about it. I may, however, call attention to a few observations of mine which tend to show that these regions were once completely buried by ice and snow during the Ice-Age. After crossing the Chang La, for instance, the traveller generally pitches his tents on the shore of the small lake of Tsultak. This lake has been dammed up by a moraine-wall which shows that a glacier, descending at some time from the Chang La, ended at this spot.

Again, I am convinced that the present form of the Pangong Lake itself owes its origin to glacial action, although the big longitudinal valley, in which the fjord-like basin of the lake is now embedded, is due to tectonic disturbances. My companion, Dr. de Terra, can show that two large faults run along the shores of the lake, one on either side.

A former higher water-level can be traced nearly everywhere. At the westernmost end of the lake there are clay deposits covered with moraine-debris, a fact which proves that these clays were laid down before the last glacial advance. Such a lake-period has been shown by Dainelli to have been in existence before the last glacial period in other parts of the upper Indus valley. The extensive stratified clay deposits in the Tankse-Drugub (or Durgu) valley also belong to this period.*

The enormous boulder-deposits which stretch between the western end of Pangong Lake and the small village of Phobrang are another point of interest. These can be nothing else than moraine- deposits which must have been brought down by glaciers descending the valleys from the Marsimik La and Keptung La, which no longer exist.

After leaving Phobrang we entered the absolutely uninhabited regions of the great plateau. Only very rarely do Changpas, the nomad herdsmen, lead their flocks of sheep and goats to the lonely grazing-grounds north of the Marsimik La. As we were likely to meet nobody for two or three months, we had taken all provisions for this period for ourselves, our ten Tibetan coolies and our two Indian servants. I knew that Captain Biddulph had crossed these high plateaux with sheep as transport-animals, and that sheep could stand the hardship of such a journey much better than ponies. My caravan therefore included 70 sheep besides 31 yaks and our riding ponies. "We next traversed the upper Chang-chenmo district, which is fairly often visited by sportsmen. Future travellers may be interested in the following notes about the geology and morphology of this region.

When traversing the big gravel-terraces to Chor-Kangma below the Marsimik La, near the junction of the Lungser valley with the Lunkur valley, the track leads along big moraine-deposits. The Lungser is a hanging valley, and on the slopes of the mountains, rising to the south of the Lunkur valley old valley-bottoms may be seen.

An interesting field for morphological study is the mountainous region lying south of the Chang-chenmo. I paid a visit to the Togum Tso, a small lake lying in the mountains due north of Phobrang. Like the Tsultak lake the Togum Tso has been dammed up by a moraine-wall. Beautifu hanging valleys can be studied in this region, while many mountains are capped by an absolutely flat plane of denudation, which in its first origin certainly dates from pre-glacial times. The country north of the Marsimik La also shows traces of its former glaciation. A trough-like valley can be seen above Spangung where the upper Eimdi river often flows in a deep gorge cut into the old valley bottom. Needless to say that in these regions, which were formerly much more glaciated than nowadays, large firn-reservoirs or 'cwms," can be seen everywhere.

The valleys here are also filled deeply with gravel-deposits, often cut into two terraces. In the area between the Rimdi river and the Chang-chenmo there rise some beautiful snowy peaks. The topography is not quite clear. On the old reconnaissance map of the Survey of India (No. 52J) there is marked a snowy peak (Pk 26/52J) * which, as far as I could make out, is identical with the one shown in the illustration.

From a geological point of view this region is interesting. Dr de Terra can prove that a big fault runs along the Chang-chenmo river.' Here the Paleozoic, Triassic and Jurassic rocks of the Karakoram are separated from older Paleozoic rocks by this big and important zone of rupture. The hot springs of Kyam are directly connected with this fault.

Further to the east we entered the hunting-grounds of Deasy and Rawling. The colours of the landscape were beautiful Especially remarkable are the deep red sandstone mountains, probably of Tertiary age, and the greenish crystalline schists and light red cliffs of Jurassic age. My plan was now to try and reach the Lmgzi-tang plain from a place called Shum on Deasy's map but we moved on until we reached the region that must be the Tomar of his map. Here we had a beautiful view of the marvellous glacier-crowned range bordering the large longitudinal valley which leads from the Lanak La (18,000 feet) to the east. The glacier-type here is extraordinary. The glaciers are creeping down from the mountains like big tongues, which often, but not always, enter the main valley. They show a type distinct from those of the Karakoram and of Turkistan. With great sheets of ice they bury the mountains, often having an inconsiderable area from which their ice is fed. The formation of such glaciers in a region which is said to have a more or less continental climate is rather a puzzle. Either the precipitation is greater than we suppose, or we can perhaps recognize in these big glaciers the last remnants of those of the Ice-Age.3 Only if we have more observations at our disposal will we be able to say more about the origin of the Tibetan glacier-type.

From this side the ascent of the Lingzi-tang was easy. Once having reached the edge of the plateau we had to wend our way for two days amongst red and greenish hills. We discovered there two small beautiful lakes and on the 21st August reached the absolutely flat clayey and sandy plain of the Lingzi-tang. The first Europeans who visited these desolate regions were the Schlagintweits (1857), Johnson (1864-5), and Hayward, as well as members of the Yarkand Mission, They discovered the easy passes leading from the Chang- chenmo valley to the plateau. These passes are known as the Chang- lung-barma and the Chang-lung-yogma ; both were used by the members of the Yarkand Mission, and lie some fifty miles or more to the west of our route. While the journeys of all these explorers led more or less from south to north, Crosby, Hedin and Dainelli crossed the northern rim of the plateau in an east-west direction. The Lokzung mountains separate the Lingzi-tang plains from the “Soda Plains" of Johnson, which are called the “Kuen Lun Plains" by Drew. To the north-east the Lingzi-tang is bordered by a range of reddish mountains, which separate it from the broad Kun-lun valley bearing in this region the name of Aksai-chin.

Generally speaking, the ranges and mountains rising here and there on the plateau consist of Jurassic and Cretaceous rocks. Especially the white hippurites limestone and the red Tertiary sandstone form bright steep-sided cliffs which are very characteristic. The big table-like surface of these plateaux is covered with sand, clay and salt deposits. Johnson has already pointed out that these thick layers of salt must be the last remnants of big lakes which have been desiccated, while Drew has given more details of these ancient lakes.

From Shum my caravan marched to the lake marked some twenty miles to the north-north-west and called Sarigh-Jilganing Kol on the Survey of India map. It is still a puzzle to me who invented this name, because before my expedition no European had ever visited it. Perhaps some members of the Yarkand Mission saw the large blue sheet of water in the distance. They may have been told by their followers that this was its name. It means " the Lake of the Yellow Valley," which is not inappropriate, for the old lake-deposits and beach-lines are of a deep yellow colour (see sketch-map at end of volume).

My explorations about this lake have absolutely proved that its waters must at one time have covered at least three or four times the area they do now. I did not visit its extreme westernmost end, but, from a high spur on the southern shore, I could clearly recognize the yellow clay deposits as far to the west as point 17,380 of the Survey map. I think the big Sarigh-Jilganing Kol must formerly have been connected with the salt-lake near Tso-tang, which we could see in the distance. To the east also the lake must have been much more extensive and was probably joined to the lakes situated on the Soumjiling plain. The beach-lines bordering this latter plain show that the Nopta Tso, the Tsaggar Tso and the Mangtza Tso formerly belonged to one large lake. The small threshold at the eastern end of the Sarigh-Jilganing is some 115 feet above the present surface of the lake.

I was also able to study the old lake-deposits. At the bottom of the sections that I examined I found a layer of dry water-plants. Similar deposits have been observed by Deasy on the shores of the Sagiiz Kol in the upper Keriva Darya district.* These layers of plants are covered by a big layer of stratified clay. It is therefore very probable that after a period of shrinkage the lake again expanded and buried the older deposits under newer layers of clay. The highest level of the lake is also marked by a distinct beach-line cut into the face of the rocky islands and promontories rising on the northern and southern shores. On the Survey Maps the lake is marked as " salt " ; this is not so, the water being only slightly brackish, and there were at the time of my visit many water-fowl on it. A lower terrace has been scooped out of the yellow clays. Great broad valleys, almost entirely dried up when we saw them, lead down to the lake from the west ""and from the south. In order that future explorers may be able to estimate any shrinkage or extension of the lake since 1927, we built a rock pyramid, height two metres, at a distance of exactly 150 metres from the southern shore.

We now have to consider the belt of rough mountains separating the Lingzi-tang from the Aksai-chin. These are called the Lokzung mountains. Drew gives the following description of this range :

" Its length is sixty miles, its width from fifteen to twenty miles. It is a region of rocky hills with flat stony valleys between them."4

This description fits that section of the mountains we had to cross between the Lingzi-tang and the Aksai-chin. I must confess that I have rarely seen such utterly barren and desolate mountains. There is practically no grass and the only vegetation available is for transport- animals is the occasional burtsa. I fixed on my plane-table a large number of peaks rising from this range, amongst which I must mention that very remarkable peak (Pk. 1/52 M), height 21,040 feet, reproduced in Drew's book on page 343. This peak visible from several points and I observed it again on my return journey via the Karakoram.

Amidst these Lokzung mountains there are broad gravel-filled valleys containing here and there small springs of fresh water. Disintegration is going on rapidly and the mountains are buried below the decomposed rocks. Huge fans and talus-slopes are to be observed everywhere. At several places the slopes show shoulder-like steps— certainly the remnants of ancient valley-bottoms. The big broad valley descending to the Aksai-chin from the snow-covered peaks north-east of Sarigh-Jilganing Kol was in its upper portion certainly glaciated during the Ice-Age. A section across its upper end shows the typical U-trough form, and old shoulders can be traced along the slopes of the mountains bordering the valley. Eight across it there has been at one spot a moraine-wall. These are certain indications but generally the rocks are so much disintegrated here that any trace of former glacial action has been destroyed.

There is no question to my mind that ice has covered these plateaux with one large sheet. Prinz has recently in his book on the glaciation of the Tien Shan and of the Kun-lun shown that the plateaux of the eastern Pamirs also were completely covered by ice during the Ice-Age.5 So also the great glaciers of the Tibetan mountains, whose tongues even to-day often reach the broad valley-like plains, were during the Ice-Age united into extensive ice-sheets covering those plains and plateaux. We need not be astonished that we do not discover on the Tibetan plateau, so far as it is without outlet, any typical through-shaped valleys which can be compared with those of the Alps. The pre-glacial dissection and erosion did not affect the Tibetan plateau very much, or if it really took place, the valleys were afterwards filled up with detritus and gravels. We know that those beautifully scooped-out glacial troughs, that we see elsewhere, can only be formed in regions where pre-glacial erosion had already excavated deep valleys. Therefore we meet these trough-valleys in the peripheral regions of the Tibet plateau.

I should like only to mention here the Pangong basin. In the form of big sheets the ice must have covered the great plateaux and mountains. After the ice had melted, few traces of the former glaciation were left in these central regions, because the strong insolation quickly destroys the rocks, and the detritus then fills the valleys. The traveller very seldom succeeds in finding glacial strise. Sven Hedin points out that probably even old moraine boulders may have been totally destroyed in these regions by insolation and corrasion. I have myself seen in the moraine deposits near Phobrang, as well as near Suget Karaul, big boulders from which only the outer crust was left. So it is not easy to discover traces of former glacial action in these regions. The best we can do is to look for moraine-deposits, the presence of hanging valleys and old shoulders, and for a broad concave form to the valleys themselves.

We made a comparatively long stay on the shores of the Aksai-chin lake. The mountains bordering the broad Kun-lun valley in the south are covered with grass, especially to the south of the Aksai-chin valley. This is contrary to what might be expected from Sir Aurel Stein's experience on the southern slopes of the Kun-lun, where he had the greatest difficulty in obtaining any grass at all for his pack- animals.6 A beautiful fresh-water spring, probably situated on a fault-line, yields plenty of clear water to the south of the lake. Like all the others of the Tibetan plateau, the bitter lake on the Aksai-chin is shrinking steadily. Old clay deposits give an idea of the former extension of the lake. The big Kun-lun valley running from the Yeshil Kol to Lake Lighten and the west follows a large fault. White quartz veins crop out here and there alongside the mountain-slopes, and silicious material is intruded along the zones of rupture. When skirting the Aksai-chin lake I discovered a considerable stream running into the lake from the east. On the slopes of the mountains bordering the Aksai-chin on the south old valley-bottoms occur ; corresponding terraces were seen on the southern slopes of the Kun-lun.

We crossed the mountains to the west of the Aksai-chin lake at a point south of Sir Aurel Stein's route. They are deeply disintegrated here and there is no water at all. The valley, from which the nullah leading to the Khitai Dawan is tributary, is dammed in its upper part by enormous moraine-boulders. Likewise this tributary leading to the Khitai Dawan and the one descending the other side of the pass to the west were formerly glaciated. This can be proved by the presence of old rounded shoulder-like terraces on both sides of the valleys. And further down, enormous deposits of morainic- boulders stretch across the upper Kara-kash valley near Haji Langar.

In order to reach the Tibetan plateau from the upper Kara-kash, it is not absolutely necessary to go by the Khitai Dawan. There is another fairly easy route which is covered by many salt lakes. Owing to considerable losses amongst our yaks I had to leave behind on the Aksai-chin a good deal of baggage and to send back a caravan from Suget Karaul to fetch it. This caravan took the alternative route, which I believe has been followed by no other European except Schlagintweit. The members of the Yarkand Mission crossed the Khitai Dawan. Drew's description of these Kun-lun plains is so good that I need say no more about them. He seems to me quite right in his statement that at one time they were covered by a large inland lake which has gradually grown smaller.

When wandering through the Kara-kash valley I was able to fix several peaks of the Kun-lun range. I could write much of this valley, but here I need only point out that at the lower ends of many of the tributary valleys there are terminal moraine accumulations. The polished rock-terraces with the appearance of roches moutonnees on the southern side of the valley tend to show that the combined ice- streams, fed from the snow-reservoirs of the Kun-lun in the north and from the plateaux-regions of the south, once united in a large glacier-stream which found its way by the Kara-kash valley downwards.

My explorations in the Kun-lun also indicate that this range was covered by big glaciers during the Ice-Age. At the maximum extension of the ice the glacier-tongues stretched down to 9200 feet on the northern slopes. I therefore conclude that it is highly probable that during the Ice-Age the whole mountainous region, from the Kun-lun mountains in the north to the Himalaya in the south, was buried under ice. It seems likely to me that during or perhaps after this glacial period a general uplift of mountainous Central Asia occurred, for everywhere in the peripheral regions, in the Kun-lun as well as in the Himalaya, the rivers, which frequently have cut for themselves deep gorges, show signs of heavy " working erosion " everywhere.

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