334 REACTION OF THE INTERIOR OF THE EARTH 



probably trachytic mountains. Overweg, so early taken 

 away from the natural sciences, found in the district of 

 Grudscheba, examined by him west of Lake Tshad, 

 according to Petermann's notices derived from his 

 journals, columnar basaltic cones, rich in olivine, which 

 have broken through the beds of red argillaceous sand- 

 stone in some cases, and of quartzose granite in others. 



A remarkable phenomenon is presented by the 

 paucity of still active volcanoes in this continent, whose 

 coasts, which are tolerably well known to us, present so 

 few indentations. May there be in the unknown 

 regions of Central Africa, especially south of the 

 equator, great basins of water analogous to Lake 

 Uniamesi (previously called N'yasse by Dr. Cooley), on 

 the shores of which volcanoes may rise like Demavend, 

 near the Caspian? Hitherto no reports of such have 

 reached us from any of the natives, who yet are great 

 travellers. 



4. Asia. 



a. THE WESTERN AND CENTRAL PORTION. 



Volcano of Demavend ( 48 ), burning, but according to 

 the accounts of Olivier, Morier, and Taylor Thompson 

 (1837), only moderately, and not smoking uninter- 

 ruptedly. 



Volcano of Medina (eruption of lava in 1276). 



Volcano Djebel el Tir (Taer or Tehr): an island- 

 mountain 895 feet high, in the Eed Sea, between 

 Loheia and Massaua. 



Volcano Peschan: north of Kutsch in the great 

 chain of the Thian-schan, or Celestial mountains, in the 

 interior of Asia; eruptions of lava within a thoroughly 



