HIGH TRANSHIMALAYAN PASSES. 263
Ki-chu with its tributaries is the greatest of all. The Shang-chu is considerably shorter, and the Ta-nakbo-chu and Rung-chu still more so; the northern tributaries to the Raga-tsangpo are mere brooks. There is only one exception: the MU-chu. But this is quite natural, for the MU-chu is the only one of these rivers which is strong enough to pierce the Nien-chen-tang-la, just as, further west, the Chaktaktsangpo pierces the Kanchung-gangri range. The Ki-chu, Shang, Ta-nakpo and Rung have their sources on the southern side of the Nien-chen-tang-la, whereas the MU-chu comes from the southern side of the Pabla. The Bara-tsangpo and Ota-tsangpo certainly come from the northern side of the range which continues eastwards from Sela-la and which should be called Pabla in its whole length.
Regarding the whole profile from Ngangtse-tso to Ye the most striking thing is the insignificant difference between the altitudes of the different passes. We have: Pongchen-la 5 371, Sela-la 5 506, Shib-la 5 349, Chesang-la 5 474, Dangbä-la 5 250 and Ta-la 5 436 m. There is a difference of only 256 m between the highest and the lowest. La-rok should not be considered, as it belongs to the very front towards the Tsangpo where the great heights have ceased. The Pongchen-la belongs to a small range just south of Ngangtse-tso. South of lower Tagrak-tsangpo there is the range which I have called Ngangtse-range, for lack of a better name, and which probably, more or less uninterruptedly, continues eastwards to the Tengri-nor; if such be the case, it is pierced by Tagrak-tsangpo, Bara-tsangpo and Ota-tsangpo. The Sela-la is on the continental water-parting and therefore the most important of all, as well as the highest. The orographical rank of the Shib-la and Chesang-la is difficult to determine. We only know that they are situated on ridges which separate the tributaries of the MU-chu from each other; and probably these ridges are simply ramifications from a high swelling or mountain knot of the Pabla at about 881/2° E. long. Dangbä-la, as shown above, is most probably situated on the S.W. continuation of the Nien-chen-tang-la, and Ta-la on a southern ramification from the same. Such is also the case with the La-rok. It should be added that the Chesong-la may as well belong to a northern ramification from the Nien-chentang-la.
On account of the general evenness, the relative altitude of the mountains as compared with the valley decreases as we proceed upwards through the valley of the Tagrak-Naong-tsangpo. On the south side of the water-parting these relations cannot be noticed, as here we do not follow one valley down, but cross many valleys at right angles. Therefore the difference of altitude between every single pass and the valley below cannot be compared one with another. Taking the valleys south of the passes we find Camp 118 at 674 m below Sela-la, Camp 119 350 m below Shib-la, Camp 120 839 m below Chesang-la, Camp 122 J41 m. below Dangbä-la and Camp 123 at 1092 m below Ta-la. Only in the case of Sela-la, Chesang-la and Ta-la can an increasing relative altitude of the pass compared with the valley south of it be noticed, or 674, 839 and 1 092 m.
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