ANNOTATIONS AND ADDITIONS. 89 



catepetl in Mexico, and only 92, 104, and 156 geogra- 

 phical miles in those of the South American volcanoes Sangai, 

 Tolima, and de la Eragua, respectively. I exclude from 

 these statements all extinct volcanoes, and all trachytic moun- 

 tains which have no permanent connection with the interior of 

 the earth. (Asie Ceutrale, T. ii. p. 16-55, 69-77, and 341- 

 356.) East of the volcano of Turf an, and of the fertile 

 Oasis of Hami rich in fine fruit, the chain of the Thian- 

 schan gives place to the great elevated tract of Gobi which 

 follows a S.W. and N.E. direction. This interruption of 

 the mountain chain, caused by the transverse intersection of 

 the Gobi, continues for more than 9J degrees of longitude ; 

 but beyond it the mountains recommence in the somewhat 

 more southerly chain of the In-schan, or the Silver Moun- 

 tains, running (north of the Pe-tscheli) from west to east 

 almost to the shores of the Pacific near Pekin, and forming 

 a continuation of the Thian-schan. As T have viewed the 

 In-schan as an easterly prolongation (beyond the interruption 

 of the Gobi) of the cleft above which the Thian-schan stands,so 

 one might possibly view the Caucasus as a westerly prolonga- 

 tion of the same, beyond the great basin of the Aral and Caspian 

 Seas or the depression of Turan . The mean parallel of latitude 

 or axis of elevation of the Thian-schan oscillates between 

 40|- and 43 N. lat. ; that of the Caucasus, according to 

 the map of the Russian Etat-Major (running rather E.S.E. 

 and W.N.W.), is between 41 and 44 N. lat. (Baron von 

 Meyendorff, in the Bulletin de la Societe geologique de 

 Prance, T. ix. 1837-1838, p. 230.) Of the four parallel 

 chains which traverse Asia from east to west, the Thian- 



