260 The Land of Deep Corrosions 
The cone and crater still preserve their form admirably, 
and Mr Coggin-Brown of the Indian Geological Survey, 
who has examined the country, considers that the volcano 
was active within the last four hundred years, perhaps at 
the time that western Ssu-chuan was so badly shaken and 
Batang engulfed. 
The whole of Western China, for a long distance east 
and north of the region we are here concerned with, shows 
similar evidences of waning vulcanism, and throughout their 
length these parallel ridges exhibit unmistakable signs of 
volcanic activity with such persistent regularity that it is 
fair to assume they are situated on a line of weakness in 
the earth’s crust which passes through Java, up the back- 
bone of the Malay Peninsula, and thence by way of Burma 
and the Shan States northwards through the region indi- 
cated as far as the plateau of Tibet. The northern half 
of this great fissure has had its day, and the centre of 
volcanic activity has shifted southwards, so that there is 
reason for supposing that a wave of vulcanism has passed 
down from High Asia, and indeed the configuration of the 
land, running out into a long narrow peninsula which finally 
tails off into a chain of islands, suggests a gradual conver- 
gence of dynamic forces from north to south. 
These evidences of volcanic activity, while by no means 
proving that the ridges have been separately heaved up into 
position, or that a semi-plastic crust has been squashed be- 
tween two irresistible forces, make one or other explanation 
plausible. On the upper Mekong at least the direction of 
the river’s flow bears no relation to the dip of the rocks in 
the almost continuous series of gorges through which it 
fights its way, for I have frequently observed in these gorges 
that the strata, tilted nearly vertical, dip in a direction either 
at right angles to that in which the river flows, or parallel 
to it, and the torrents also may cleave their way through to 
the main gorge between vertically-tilted slabs in one place, 
and across their sawn edges in another. 
But without assuming that any one of these rivers is 
alone responsible for carving out its valley, evidence is not 
lacking that they have scoured their beds to a considerable 
depth—indeed it could not be otherwise. In a limestone 
gorge on the Mekong I noticed across the river the remains 
