516 THE DASH FOR LHASA.
of low hills separated from one another by gullies and small brooks. On the left we had a low range, on the right a flat, open plain, or sort of extensive cauldron valley, with regard to the real value of which I was unable to obtain any clear conception. While on the one hand it resembles an independent self-contained basin, it is more probable that it only forms part of the basin of the Satschu-tsangpo or the Selling-tso. In two small thresholds black argillaceous schist cropped out at 6o° S., while the loose pieces of rock consisted of a hard variety of rock, resembling light-coloured porphyry.
After that the country was very level, and were it not that the surface was so sodden and so disagreeably softened by the rain, the going would have been particularly good. By this we had descended nearly 1 oo m. below the pass I have mentioned. The grazing was miserably poor. The incredible amount of tame-yak dung proved that we were travelling along a much frequented road. Southwards the country appeared to be flat; in fact there were no higher mountain-ranges at all in that direction, only stretches of low rounded hills.
Beside a little spring, with grass all round it, we found a big Tibetan trading caravan resting. It consisted of 25 to 3o men, with 30o yaks, laden with tea sewn up in bales. They said they came from the neighbourhood of Kum-bum, and were bound for Taschi-lumpo. When actually marching the caravan was divided into several groups, and the men travelled on foot. They were journeying by night only, so as to give their animals an opportunity to graze by daylight, and were making only short stages.
At the next spring, just south of the road, we pitched our own tent, Camp LI, at an altitude of 4836 m. Thus we had now reached a somewhat lower part of the Tibetan plateau country; yet it was not until the following stage that we got down below the level of Mt. Blanc.
After a beautiful morning, the heat being almost oppressive, a violent thunderstorm burst over us in the afternoon, while the hail beat so furiously upon our tent that it almost threatened to flatten it level with the ground. This was followed by three hours of rain. Strange to say, the sky all round the horizon was clear; the heavy clouds, which were discharging their contents upon us, appeared to hang stationary above the cauldron valley in which we were encamped. The violent crashes of the thunder gave rise to a peculiar and unusual acoustic phenomenon, such as I had never experienced before. The thunder-clap, after vibrating for a long time and with dwindling force, died away at a great distance with a clear metallic echo like that of a church bell. This peculiarity may possibly be in some way dependent upon the general configuration of the country. At any rate that configuration affected the rather crisp south-easterly wind which during the night swept along the northern foot of the hills, driving before it dense masses of cloud, which seemed actually to follow a predetermined course, like water flowing down a river-bed. Although our camp stood quite close to the path of the wind, it remained in almost perfect quietude.
Aug. 4th. According to the men of the yak caravan, the district in which we then were is called Amdo-motschu. Thence they estimated it to be five days to Naktschu, and to the pass of Lani-la seven, though evidently short days.
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