366 VOLCANIC REGION OF CENTRAL ASIA. 



uated between the first and second system of moun- 

 tains. The principal seat of volcanic action appears 

 to be in the Teen-shan. Perhaps the colossal 

 Bokhda-ovla is a trachytic formation, like Chimbo- 

 razo." On both sides of the Teen-shan violent 

 earthquakes occur. The city of Aksou was entirely 

 destroyed at the commencement of the eighteenth 

 century by a commotion of this nature. In Eastern 

 Siberia the centre of the circle of shocks appears 

 to be at Irkutzk, and in the deep basin of the Baikal 

 lake, in the vicinity of which volcanic products are 

 observed. But this point of the Altaic range is the 

 extreme limit of these phenomena, no earthquakes 

 having been experienced farther to the west, in the 

 plains of Siberia, between the Altaic and Uralian 

 ranges, or in any part of the latter. 



The volcanic territory of Bichbalik is to the east 

 of the great depression of Asia. To the south and 

 west of this internal basin we find two cones in ac- 

 tivity, Demavend, which is visible from Teheran, 

 and Seiban of Ararat, which is covered with vitreous 

 lavas. On both sides of the isthmus between the 

 Caspian and the Black Sea springs of naphtha and 

 mud-eruptions are numerous. 



On the western margin of the great depression, if 

 we proceed from the Caucasian isthmus to the north 

 and north-west, we arrive at the territory of the 

 great horizontal and tertiary deposites of Southern 

 Russia and Poland. Here we find igneous rocks 

 piercing the red-sandstone of Jekaterinoslav, together 

 with asphaltum and springs impregnated with sul- 

 phurous gases. 



A phenomenon so great as that of the central de- 

 pression of Asia, which resembles the circular val- 

 leys of the moon, could have been produced only by 

 a very powerful cause acting in the interior of the 

 earth. This cause, while forming the crust of the 

 globe by sudden raisings and sinkings, probably filled 



