The Land of Deep Corrosions 257 
in the Salween valley, causing the streams which flow down 
that side to cut their way back at the head much more 
rapidly ; indeed, the comparative volumes of the streams 
flowing to the Salween and Mekong respectively make this 
abundantly evident. Other things remaining unchanged, 
the final result of this must be to divert the Mekong itself 
at some point south of the arid region, beyond which this 
great difference of precipitation is not found (latitude 29°), 
and cause it to flow into the Salween, especially as it already 
flows at a very considerable elevation above that river. 
The Mekong valley has the further peculiarity already 
alluded to, that a rainy belt is interpolated between the arid 
region north of Yang-tsa and what may be called the dry 
region, scarcely so intense as the former, of the middle 
Mekong. This rainy belt, while not comparable in richness 
of vegetation to the Salween forests, nevertheless receives 
a heavy summer rainfall, due perhaps to peculiar local 
conditions. 
In the present chapter I propose to bring forward a few 
facts which may help to give some idea of what tremendous 
forces have been moulding this land into its present fantastic 
form, and at the same time to hazard a few suggestions as 
to the means by which this may have been accomplished, 
Viewed as a whole, the region seems to have been 
subjected to terrific lateral pressure, either acting simul- 
taneously from east and west, or more probably from one 
side only, the other side being crushed against an unyielding 
barrier which, by preventing any actual movement of the 
mass so caught, has compelled it to ruckle up in parallel 
ridges as one might ruckle up a piece of cloth. 
This, indeed, is the appearance which the country 
presents, and a glance at the map of Asia will suggest a 
cause for this squeezing, namely the proximity of the two 
great mountain ranges of Tibet, the Himalaya and Trans- 
Himalaya, whose axes of uplift run east and west ; and it is 
not impossible that the uplift of these stupendous ridges 
was accompanied by a slight lateral motion eastwards, 
jamming a comparatively narrow tract of country against an 
unyielding mass in Western China, and thus forcing it to 
occupy less space, which of course it could only do by 
throwing itself into folds at right angles to the direction 
W. T. 17 
