RECENT VOLCANOES. 273 



that build up the north-western cone have been irregularly cut into 

 by denudation. It is from the south-east cone that vapour issues ; 

 it is given forth in considerable quantity, so that although there may 

 not have been any outpouring of lava of late years, yet the volcano 

 has not entirely ceased to be active. It is probably in the Si solfata- 

 ric " stage. It is unusual for an active volcano to rise at such a 

 distance from the seashore : K6h-i-Tafda"n is about 240 miles distant 

 from the Arabian Sea. But as Asia is the most massive of all the 

 continents it is naturally there that such exceptions may be ex- 

 pected. 1 Geologists have pointed out that volcanoes are formed 

 where great and sudden differences of level occur in the surface 

 of the earth's crust, and nowhere are these differences so much 

 marked as along some of the sea-coasts, which would explain the 

 position of so many volcanoes near the sea. It is quite possible that 

 considerable differences of level are concealed by the enormous 

 thickness of recent deposits in the deserts- of Central Asia. 



I did not ascend up to the summit of the mountain, but the 

 vapour appears to issue from the southern side of the peak. It 

 issues at regular intervals of time, in very large volumes visible from 

 a distance of several miles. 



Where sections of the lavas are exposed in ravines they exhibit 

 normal characters ; flow-structure is very distinctly seen and the 

 scoriaceous nature of both the upper and lower portions of the flow 

 is also distinctly shown. The lower scoriaceous portion is often 

 quite cavernous, some of these natural caverns being spacious 

 enough to be used as dwellings. Many other dwellings have been 

 artificially excavated in the soft ash-beds. As it often happens in 

 volcanic areas this cavernous lower portion of the lava affords an 

 easy passage to water, which is frequently seen gushing out from 

 the junction of the lava and agglomerate. The spring known as the 

 " Fountain of iMoses M in the valley above Timi is of that nature. 



» Some of the American volcanoes, though not so far removed from the ocean as 

 the K6h-i-Tafdan,are by no means in the neighbourhood of the seashore; for instance, Coto- 

 paxi is 160 miles distant from the Pacific Ocean, while Popocatepetl is situated at 160 miles 

 from the Pacific Ocean, and 140 miles from the Gulf of Mexico, 



( 95 ) 



