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Digital Archive of Toyo Bunko Rare Books

the countries of the subtropical zone, inclusive of the desert regions of North Africa
and South Asia, have gone through a pluvial age, which is generally supposed to
have been contemporary with the ice age in northern countries. In 16 points Blancken-
horn shows how the pluvial epochs corresponded with the glacial epochs. ¹

The same agencies which brought with them a pluvial epoch in North Africa
and South Asia, and generally the whole subtropical zone, forced also the glaciers
of Himalaya and Kara-korum to increase and advance to much lower levels than
nowadays. The original cause has been the same, but while the increased precipita-
tion formed lakes in warmer countries, it accumulated snow and ice in the colder
regions, such as the two mountain systems mentioned. On the highland plateau of
Tibet the temperature must have been sufficiently low to allow the entrance of
an ice age, but even then, and on account of the protection of the southern mountain
systems the precipitation has not been sufficient to cover the highland with a cap of
ice. There are glaciers, although sporadic, rare and small, all over Tibet, and they
advanced considerably at the same time as those of Himalaya and Kara-korum. But
otherwise I have in vain searched for any traces of an ice age in the country.

The effect of the increased precipitation is best visible in the beach-lines and
strand-terraces of the lakes, of which some have stood at a level 133m. higher than
now. During the same period the Manasarovar received a much greater volume of water
from its affluents than now, as is also seen from the old fluvial terraces of Tage-
tsangpo and Samo-tsangpo. The surface of the lake does not need, however, to
have stood much more than 2m. higher than in 1907. Through the channel of
Nganga or Ganga the lake was continually drained and kept at a constant level.

In the same way the Rakas-tal was constantly filled, and the Satlej flowed out
of this lake, already here a mighty and rushing river, strong enough to cut out the
deep valley past Laling-tak and Dölchu-gompa. This state of things may have under-
gone periodical changes corresponding to the glacial and inter-glacial periods. At
that epoch nobody would have been in doubt where the real source of the Satlej
was situated. For the Tage-tsangpo comes from the Himalayan side which is higher
and more exposed to the precipitation, and therefore able to give rise to the greatest
river. The relative volumes of different affluents must have been the same as now.
Therefore I have called, and still regard the source of the Tage-tsangpo as the
genetic source of the Satlej.

The pluvial epoch however, proceeds towards its end. The salt lakes of the
highland plateau have dwindled gradually and left behind a series of strand terraces.
The Manasarovar and Rakas-tal still have nearly the same outlines as before, although
their levels are sinking slowly and irregularly. Finally the historical time sets in.
The scholars I have quoted above, except Huntington, agree that the historical time