ON ITS EXTERIOE. VOLCANOES. 415 



schan (whose lava-yielding eruptions, from the year 89 

 to the commencement of the seventh century, have 

 been severally recorded in Chinese works) is only 172 

 geographical miles from the great Alpine Lake Issikul, 

 situated on the south side of the Temurtutagh (a western 

 portion of the Thian-schan), and 208 miles from Lake 

 Balkasch which is 148 miles long. ( 568 ) The great Dsai- 

 sang Lake (near which I found myself in 1829, in 

 Chinese Dsungary) is 360 miles from the volcanoes of 

 the Thian-schan. There is, therefore, no deficiency of 

 inland waters, although, indeed, not in such near prox- 

 imity as that of the still active volcano of Demavend 

 (in Persian Mazanderan) to the Caspian Sea. 



If we admit that masses of water, oceanic or in- 

 land, are not requisite for the maintenance of volcanic 

 activity, and that, as I am inclined to believe, islands 

 and coasts are richer in volcanoes only because the 

 upheaval effected by internal elastic forces is accom- 

 panied by adjacent depression in the bed of the sea( 569 ), 

 so that an area of elevation borders on an area of sub- 

 sidence, and at the limit between these areas great and 

 profound clefts and fissures are occasioned, then we 

 may conjecture that, in the zone of Central Asia which 

 is included between the parallels of 41 and 48 K, the 

 great Aralo-Caspian basin of depression, as well as the 

 considerable number of lakes (some arranged in chains 

 and others not so arranged), may have occasioned, between 

 the Thian-schan and the Altai Kurtschum, the existence 

 of phenomena similar to those which elsewhere are found 

 in proximity to the sea-coast. We know by tradition that 

 many comparatively small pieces of water which now 

 form chains of lakes (like beads on a necklace, lacs a 



