CHAPTER XVI
THE ANCIENT CLIMATE OF IRAN
IN order to appreciate fully the great historic significance of the changes of climate of which we have found so abundant evidence in Chinese Turkestan, we must now endeavor to ascertain over how wide an area the changes have extended. Two regions, Iran and the Caspian basin, which I studied in 1903-04 as a member of the Pumpelly Expedition, shed much light on the subject, because, being arid and containing . lakes without outlets, changes of climate produce effects more marked than those produced in moister regions where the lakes all have outlets. Iran is a convenient term for the great region of basins and mountains covering Persia, Afghanistan, and Baluchistan. In the first volume of "Explorations in Turkestan," I have described the extremely arid condition of Iran to-day, and have set forth various reasons for believing that climatic conditions have not always been the same. Accordingly, I shall here consider merely a few of the chief lines of evidence, in order to show how closely the phenomena of Iran agree with those of the Lop and Turfan basins from one thousand to two thousand miles farther east.
Observant travelers in the more arid parts of Iran have almost without exception been much impressed with the unmistakable evidences that a change of some sort has overwhelmed the country. Ruins are incredibly numerous. Mighty cities of the dead crowd such places as Seyistan, the
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