国立情報学研究所 - ディジタル・シルクロード・プロジェクト
『東洋文庫所蔵』貴重書デジタルアーカイブ

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4 1a

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300

THE TSANGPO FROM KARU TO SI-JIGATSE.

quite near us; a little north branch of the river sweeps immediately along the foot of the rocks; the road is here laid with stones and protected by a low stone wall. The valley and mountain of Changri are left on our right.

We now come up on the hills of gravel and shingle, the foot of which is washed by the Tsangpo, making the slope very steep down to the river. It is on

the top of this terrace we again camp at Ta-nakpo. The brook Ta-nakpo-chu had now diminished considerably, to about 5 cub.m., which chiefly seems to depend on the irrigation canals, many of which now stood filled with water from the brook.

Both on my journey down to Shigatse and back to Ye the weather was very windy: hard, westerly wind especially from noon till late in the evening. Riding westward one had this wind straight in the face, and even with well protected eyes it was sometimes impossible to look up. From higher points, as Lamo-tang, the whole valley seemed to be filled with a compact yellow stream of drifting sand-clouds, rushing down over the river-bed to the east. No doubt this annual sand-loaded wind is one of the causes of the general barrenness of the valley. Sand-dunes are also a common phenomenon, and only occasionally does the meagre vegetation get time to bind them. The wind is a second agency assisting the river to work out the valley. The great difference of temperature between winter and summer, day and night, the capillar frost, the barrenness of the rocks, the rains, — everyone of these agencies accelerates the weathering and decomposition of the mountains. The finest detritus is carried away by the wind, and the corrosion of the drifting sand again attacks the hardest rocks. Sand-dunes are formed on the level bottom of the valley, and even between the river-branches. During the high-water season they are again carried away and form new sand-banks lower down the course. These sand-banks get transformed into new dunes. Thus there is a constant wandering of solid material down the valley under the action of wind and water, both tending eastwards. The air, the water, and the solid material, everything is wandering from west to east through this great furrow between the Himalaya and Transhimalaya. From the side-valleys much material is also brought down into the Tsangpo valley; but the tributaries are protected against the wind. The Tsangpo is the great common recipient for wind, water and detritus. In the side-valleys the action of the water is nearly at rest in winter, but in the Tsangpo valley the water always carries out its work, though, of course, on a much greater scale in summer than in winter.

At Karu, on March 3oth, I was told that the windy season would continue for another two months. About the middle of May the wheat and peas are sown, and the barley some I o days later. When the crop is about 3/4 foot high, the wind has ceased. At the end of June or in the beginning of July the rain sets in, and during the rainy season there is no wind. The amount of rain varies year by year, sometimes it falls in abundance, sometimes only in light showers, and much interrupted by clear weather. In the middle or end of September the harvest is brought in. Just now, or at the end of March, the frozen stretches of the river