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0252 Southern Tibet : vol.2
南チベット : vol.2
Southern Tibet : vol.2 / 252 ページ(白黒高解像度画像)

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doi: 10.20676/00000263
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Admitting that a general desiccation is taking place all over Tibet, the next
question is: why? What is the cause of this desiccation? We observe the facts and
see the obvious results, but where is the agency?

In order to find an answer we may examine some of the researches made in
another Asiatic country, the situation and configuration of which may allow us to
compare it with Tibet, namely, Persia. ¹

In Persia the question will have to be put thus: are there any evidences
of a former pluvial or lacustrine epoch in Persia, which may be supposed to have
taken place at the same time as the glacial period in Northern countries? During
my last journey through Persia I became convinced that the depressions, Kavir, in
the north-eastern part of the country must once have been filled with salt lakes.

Professor E. BRÜCKNER has compiled a most interesting monograph on the
changes of level in the Caspian Sea during historical time, and he gives the great
occurrences of change in the following table:

Anno 915—921 . . . . . . . . . . + 8.2 metres
XIIth century . . . . . . . . . . . — 4.0 »
Anno 1306 . . . . . . . . . . . . + 11.2 »
Anno 1638 . . . . . . . . . . . . + 4.0 »
Anno 1715 . . . . . . . . . . . . + 0.3 »

The oscillations of the level of the Caspian run, as Brückner finds, absolutely
parallel with the periodicity of precipitation in the regions which drain to that sea.
And as he has found that nowadays glaciers and lakes change simultaneously, he
has no doubt that the case was the same in Diluvial times. In the interior of the
continents where glaciers had no opportunity to form, lakes were formed instead.
Thus the area of the Caspian was about twice as great as now, the area of Lake
Aral at least thrice, and most of the Kisil-kum and Kara-kum deserts were covered
with water. ²

In 1903 R. PUMPELLY found old Caspian shore-lines near Baku at heights of
300, 500 and 600 feet. ELLSWORTH HUNTINGTON who travelled in eastern Persia
near the Afghan frontier down to Seistan, has discovered some unmistakable proofs
of a profuse precipitation during an epoch which is supposed to have been equivalent
to the glacial period in higher latitudes. The Quaternary deposits and terraces of
Persia seem to be the result of a series of climatic oscillations, and in Seistan
Huntington reckons as many as 14 or 15 oscillations between dry and moist periods.
At Seistan and probably elsewhere, a series of lakes appear to have occupied the
basin during the Glacial period. At the lake of Kogneh Huntington found river-
and lake-terraces showing that fluvial and lacustrine periods have alternated with