The ascent was steep and difficult, up a stony valley bounded by
precipices; in this the river flowed in a north-west direction, and
we were obliged to wade along it, though its waters were bitterly
cold, the temperature being 39 degrees. At 15,000 feet we passed from
great snowbeds to the surface of a glacier, partly an accumulation of
snow, increased by lateral glaciers: its slope was very gentle for
several miles; the surface was eroded by rain, and very rough, whilst
those of the lateral glaciers were ribboned, crevassed, and often
conspicuously marked with dirt-bands.

A gently sloping saddle, bare of snow, which succeeds the glacier,
forms the top of the Tunkra pass; it unites two snowy mountains, and
opens on the great valley of the Machoo, which flows in a part of
Tibet between Sikkim and Bhotan; its height is 16,083 feet above the
sea by barometer, and 16,137 feet by boiling-point. Nothing can
be more different than the two slopes of this pass; that by which I
had come presented a gentle snowy acclivity, bounded by precipitous
mountains; while that which opened before me was a steep, rocky,
broad, grassy valley, where not a particle of snow was to be seen,
and yaks were feeding near a small lake not 1000 feet down. Nor were
snowy mountains visible anywhere in this direction, except far to the
south-east, in Bhotan. This remarkable difference of climate is due
to the southerly wind which ascends the Tibetan or Machoo valley
being drained by intervening mountains before reaching this pass,
whilst the Sikkim current brings abundant vapours up the Teesta and
Lachoong valleys.

Chumulari lies to the E.N.E. of the Tunkra pass, and is only
twenty-six miles distant, but not seen; Phari is two marches off, in
an easterly direction, and Choombi one to the south-east. Choombi is