ON ITS EXTEEIOE. YOLC ANDES. 331 



not definitely circumscribed, and cannot, therefore, be 

 traced as proper lava-currents of small breadth. Tris- 

 tan da Cunha (37 3' S. lat., 11 27' W. long.), disco- 

 vered by the Portuguese in 1506, a small circular 

 island of 6 miles diameter, having for its centre a 

 conical mountain, which Capt. Denham describes as 

 being about 8,300 feet high, composed of volcanic rock. 

 (Petermann's Greogr. Mittheilungen, 1855, No. III. S. 

 84.) South-east of Tristan da Cunha, in 53 S. lat., is 

 the also volcanic Thompson's Island ; and intermediate 

 between them, in the same line, is (rough Island, also 

 called Diego Alvarez. Deception Island, a narrow, 

 ring-island, with a small opening (62 55' S. lat.); and 

 Bridgman Island, belonging to the South Shetland 

 group, are both volcanic ; and amidst beds of ice, pumice, 

 black ashes, and obsidian, perpetually send forth hot 

 vapours. (Kendal in the Journal of the Greogr. Soc. 

 vol. i. 1831, p. 62.) In February 1842, flames were 

 seen to issue at once from thirteen points of the Ring 

 of Deception Island. (Dana in U.S. Explor. Exped. vol. 

 x. p. 548.) It is remarkable that while so many other 

 islands in the Atlantic are volcanic, neither the small 

 and quite flat Island of St. Paul (Penedo de S. Pedro), 

 one degree north of the equator (a very slightly lami- 

 nated greenstone-schist, passing into serpentine) ( 47G ), 

 nor the Falklands (with their quartzose clay-slates), nor 

 South Georgia, nor Sandwich Land, appear to present 

 any volcanic rocks. On the other hand, a region of the 

 Atlantic about 20' south of the equator, and 19 40' 

 west long, from Greenwich, is considered to be the seat 

 of a submarine volcano ( 477 ). Krusenstern saw columns 

 of black smoke rise from the sea in this neighbourhood, 



