the Last Town im China 119 
Ascending the south slope we found at the limit of trees 
spruce and /unzferus, the latter not like our English juniper 
bushes, but big trees. These ceased at an altitude of little 
over 14,000 feet, and alpine grass-land, with narrow strips 
of dwarf juniper under the protection of the rocks, extended 
to the summit. On the north-facing slopes, however, spruce 
and larch were the limiting species, extending to within 
600 feet of the summit, to be succeeded by a thick belt of 
dwarf rhododendron which scarcely died out before the 
summit was reached, the belt of alpine grass-land being 
correspondingly reduced. 
This marked peculiarity of south-facing valleys is due, 
firstly to the more rapid melting of the snow in spring, 
whereby the only available supply of water is removed at 
the very outset of the vegetative season, and the un- 
protected young shoots suddenly exposed by the rapid 
stripping off of the warm snow blanket; secondly to the 
havoc wrought by the dry, rainless local winds to which 
the south-facing valleys are liable throughout the summer. 
Looking eastwards from the pass, there came into view 
an extraordinary wall of limestone towers and buttresses 
crowning the Mekong-Yang-tze divide. These splintered 
cliffs and bare screes testified to the weathering work 
performed by dry denuding agents—a wide range of tem- 
perature with rapid alternations, the effects of wind, the 
splitting action of frost and so on—and were in strong 
contrast to the graceful pyramids carved out by water 
erosion on the far more rainy Mekong-Salween water- 
shed. 
This chain of limestone towers can be traced from 
Pei-ma-shan in latitude 28° 15’ to latitude 29° and between 
these two points we crossed the watershed by four different 
passes. Indications of previous glaciation were everywhere 
visible, and there can be little doubt that this ridge has had 
its rainfall enormously curtailed here by the very consider- 
able elevation of the Mekong-Salween watershed further 
west, which thus, as previously stated, intercepts the 
bulk of the monsoon rains from the south-west. 
The descent to the Tibetan village of Tsa-lei occupied 
nearly three hours, and it was dark when we arrived after 
fourteen hours in the saddle. 
