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THE TSANGBO, OE BRAHMAPUTRA. 81
round their orifices crystal margins bristling with long stalagmites. Most of
the lakes in this district have either been filled with alluvia or exhausted through
their emissaries. Amongst the largest that still survive is the Yamdok, or Palti,
which is figured on D'Anville's and subsequent maps as almost ring-shaped, or like
a moat surrounding a citadel. The island, which is sometimes represented rather
as a peninsula, rises 2,250 feet above the surface of the lake, which is itself 13,350
feet above sea-level. According to Manning it is slightly brackish, although the
pundit who visited its northern shore found its water perfectly pure and sweet. It
is said to be very deep, but it is uncertain whether it forms a completely closed
basin or drains through a western outlet to the Tsangbo, from which it is separated
on the north by the lofty Khamba-la group.
North-east of Lake Palti the Tsangbo is joined by the Kichu, another " holy
stream " which waters the Lassa valley. Nain Singh, who visited the district in
1875, saw this valley stretching eastwards some 30 miles, and then disappearing
towards the south-east between the hills. But in 1877 another Hindu explorer,
instructed by Harman, was able to follow the course of the river for over 180 miles.
This explorer first followed the Tsangbo to the extremity of the valley seen by
Nain Singh from a distance, but was afterwards obliged to make a great detour in
order to avoid a deep gorge into which the river plunged. Nevertheless he came
upon it again some 20 miles from the point where he had left it, and then
ascertained that it made a bend northwards before resuming its normal course
towards the east and south-east. At the farthest point reached by him he saw a
fissure opening in the mountains in the same south-easterly direction, and was told
by the natives that the Tsangbo escaped through this fissure to traverse a tract inha-
bited by wild tribes -and a country beyond it belonging to the British Government.
At Chetang the Tsangbo valley is about 11,250 feet above sea-level. Yet at this
elevation the river, which already drains an area of 80,000 square miles, has a
volume equal to that of the Rhine or Rhone. When seen by Nain Singh its waters
were comparatively low, yet the breadth of from 1,000 to 1,500 feet assigned to it by
him, combined with its great depth and velocity, implies a volume at that season of
rather more than 28,000 cubic feet per second. But during the floods of June and
July the stream overflows its banks for several miles, and the discharge cannot then
be less, perhaps, than 700,000 cubic feet, assuming the rise to be no more than 16
feet, as the natives assert. Below Chetang, in East Tibet, the Tsangbo still receives
a large number of copious streams, and flows through one of the wettest regions on
the globe, so that it must carry an enormous quantity of water to the Indian Ocean.
Yet, to judge from the maps, it seems to lose itself, for its lower course remains still
uncertain, oscillating between the Brahmaputra and Irawady. Francis Gamier
even luggected that limestone rocks full of caverns, like those scon by him in many
parts of China and Further India, occupy the south-east portion of Tibet, and that
the Tsanglx) here flows partly underground and ramifies into several basins. But
what little is known of the geology of East Tibet seems opposed to this theory.
Limestones occur only on the Yunnan frontier, the rest of the country being com-
posed of crystalline rocks covered with glacial clays.