IIIF Color HighRes
National Institute of Informatics - Digital Silk Road Project
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| IIIF Color HighRes |
| Southern Tibet : vol.7 |
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Citation Information
RICHTI-iOFEN.
322
accepts the name Central Asia, which had been abused in so many ways, only under condition that the cenfral regions should be regarded in comparison with the peri-
pheric ones.'
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: i . 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 contains 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; and 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 , and 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 formation 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
I Op. cit., p. 5.
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