IMPORTANCE OF CLIMATIC RECORDS 363 



conditions have never been more severe than those of Canada today, and 

 where thesial conditions have been like those of Texas, it is in vain to 

 look for any very marked evidences of a climatic strophe. Under more 

 extreme conditions, however, a much slighter change will produce far 

 more manifest and permanent results. For instance, a change from the 

 climate of northern Canada to that of Greenland would cause glaciation, 

 and a change from the climate of Utah to that of Montana would cause 

 the expansion of inclosed lakes. Hence, in studying the Pleistocene 

 strophe, attention has been devoted mainly to glaciated countries, on the 

 one hand, and to arid regions, where the lakes have no outlets, on the 

 other. Glacial deposits, including till-sheets and moraines, are com- 

 monly laid down in regions of more or less relief, where erosion is 

 comparatively active. Therefore they are liable to relatively rapid de- 

 struction. Moreover, the deposits of one arsial epoch are in imminent 

 danger of being destroyed in the next. In arid basins the case is very 

 different. Erosion is at a minimum or absent, and the deposits of one 

 epoch are usually laid immediately on those of its predecessor. Every- 

 thing combines to preserve a complete record of all the changes, climatic 

 and otherwise, to which the given region has been subjected. Generally 

 the record is inaccessible. If, however, by uplift or otherwise, it is ex- 

 posed and dissected, it furnishes a most valuable means of supplementing 

 the glacial record by filling in the gaps, and by indicating the occurrence 

 of early events whose record in colder lands has been completely effaced 

 by successive incursions of ice. , 



The Basin of Seyistan, in eastern Persia 



awneral description of the basin 



In the arid basins of Seyistan, in eastern Persia, and of Lop and Tur- 

 fan, in Chinese Turkestan, such records of the Pleistocene strophe are 

 found. The evidence of all three basins appears to agree in indicating 

 that the strophe was very complex, and that there were several cycles of 

 climatic change preceding those of which the record is preserved in 

 glaciated regions. The basin of Seyistan, which I have described in 

 "Explorations in Turkestan," comprises a mountain-girt area of about 

 200,000 square miles in southwestern Afghanistan, northwestern Balu- 

 . chistan, and eastern Persia. The climate is so dry that many of the 

 streams wither away and are lost in the vast piedmont slopes of gravel 

 at the base of the encircling mountains. The rest unite to form the 

 Helmund river, which flows toward the corner M^here Persia joins 

 Afghanistan and Baluchistan. There the river gives rise to two lakes 

 lying at almost the same level. One, called the Hamun-i-Seyistan 



