The principal geographical result of YOUNGHUSBAND's famous mission to Lhasa was the excellent map drawn of the Tsangpo valley. Of the tributaries only the Nyang-chu and Maryum-chu were completely surveyed as well as the lower part of the combined Ki-chu. Of the other tributaries not much more could be touched than had been seen by Nain Sing. But from their triangulation stations RYDER and his comrades had a much wider view than Nain Sing could get from the road. Thus, for instance, Raga-tsangpo has got a great number of northern tributaries and Amchok-tso is an important addition. The Chaktak-tsangpo and Tsa-chu-tsangpo have been enormously improved. Ryder's map of the Tsangpo and of the courses of its tributaries so far as they could be seen, will for ever remain a foundation for future exploration in these parts of Tibet. Thus his map has a greater fundamental and historical importance than any other in existence, only except the Chinese maps, which must be considered for a much greater area. As RAWLING's and Ryder's expedition was for a great part of the journey separated into two parties, it often carried out so much work as two ordinary expeditions would have done.
Ryder crossed three southern tributaries, two of them called Shap Chu and Sakyatrom Chu, and then followed the lowest part of the Chi Chu. South of Kura La ( i 7,900 feet) he touched the headwaters of Chi Chu. From Sheru La (i 7 ,600 feet) a very small tributary goes down to the Tsangpo. Between Chi Chu and the brook of Sheru the Tsangpo was found to run between rocky hills with snow-peaks on either side.
A short distance above Lhatse Captain WOOD found, on October 26th, a ford, by which the ponies were able to cross the Tsangpo. Wood says of the valley of the Raga-tsangpo : I that it is narrow, running almost due east and west, parallel to and about 3o miles to the north of the main river ... On November 5 we crossed the Ku La (16,70o feet),2 situated at the headwaters of the Raga Tsangpo, and by a steep descent dropped into the valley of a small stream draining into the Tsangpo». Near Saka-dsong Wood ascended a peak to the north (19,30o feet), ''from which he had a fine view north up the valley of the Charta Tsangpo.
I Exploration and survey with the Tibet frontier Commission, and from Gyangtse to Simla viâ Gartok. By Major C. H. D. Ryder. Geographical Journal, Vol. XXVI. October 1905, P• 385. 2 Identical with Nain Sing's Curia Pass.
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