Southern Tibet : vol.7 / 484 ページ（白黒高解像度画像）

0484	Southern Tibet : vol.7
南チベット : vol.7

322

accepts the name Central Asia, which had been abused in so many ways, only under
condition that the *central* regions should be regarded in comparison with the peri-
pheric ones.¹

Richthofen starts from the fact that the rivers are much better known than
the mountains, and, therefore, he uses the hydrography for determining the boundaries
of his different Asiatic regions. He separates the regions without outlet from those
from which the water flows to the ocean. Thus Richthofen obtains the following
three great regions or physico-geographical provinces: 1. Central Asia, which is
bounded by the Tibetan Plateau to the south, the Altai to the north, the water-
parting of the Pamirs in the west, the water-parting of the Chinese Rivers, and the
Khingan Mountains to the east. 2. Peripheric regions are all those, from which the
rivers flow to the ocean or to the Caspian and to Lake Aral. 3. The intermediate
zone, situated between the first two and where regions which formerly had an outlet
have been changed into ocean-drained or *vice versa*.

In the central regions all the products of decomposition have remained and
subaerial deposits are common; in the peripheric regions lacustrine and fluvial deposits
prevail. The final goal of the central destruction is to fill up all depressions and
to level all mountains until a plain is formed. In the peripheric regions, on the
other hand, the relative differences of height are more considerable. In the basins
without outlet the evaporation is greater than the precipitation, so that the depressions
cannot be filled with water, but only filled and levelled by detritus material in the
course of time. Such depressions are, as a rule, steppes, and as their ground con-
tains salt they could be called salt steppes.

What Richthofen says in general about all central depressions in Asia could
particularly be said about those in Tibet:

Ist die Depression rings geschlossen, so breitet sich in der Mitte ein Salzsee aus,
der in der Regel von salzigen Sümpfen umgeben ist; und in mancher ist nur ein Salzsumpf
vorhanden, der zu einer gewissen Jahreszeit ganz austrocknen kann. Öffnet sich aber die
Depression nach einer Seite gegen eine andere, tiefer gelegene, so fliessen die vereinigten
Gewässer nach dieser ab, und dann befindet sich der Salzsee in dem Boden der tiefsten
Depression des ganzen Systems.

In Richthofen's opinion the changes of climate are the chief factor in the for-
mation of self-contained basins, and if such a basin again gets an outlet, it is also
a new change of climate that is the cause. The precipitation does not need a
considerable augmentation for providing a basin with an outlet.

Richthofen even believes that the Koko-nor is in a state of rising and that
its basin is approaching its flowing over. Between the feeders of the Yang-tse there
are certain self-contained basins which indicate that the whole country around not

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