chap. vi. Volcanic Islands. 145 



in hardly any instance, that the whole body of matter, 

 forming a volcanic island, has been erupted at the 

 level, on which it now stands : the number of dikes, 

 which seem invariably to intersect the interior parts of 

 every volcano, show, on the principles explained by 

 M. Elie de Beaumont, that the whole mass has been 

 uplifted and fissured. A connection, moreover, between 

 volcanic eruptions and contemporaneous elevations in 

 mass l has, I think, been shown to exist, in my work on 

 Coral Reefs, both from the frequent presence of upraised 

 organic remains, and from the structure of the accom- 

 panying coral-reefs. Finally, I may remark, that in 

 the same Archipelago, eruptions have taken place within 

 the historical period on more than one of the parallel 

 lines of fissure : thus, at the Galapagos Archipelago, 

 eruptions have taken place from a vent on Narborough 

 Island, and from one on Albemarle Island, which vents 

 do not fall on the same line ; at the Canary Islands, 

 eruptions have taken place in Teneriffe and Lanzarote ; 

 and at the Azores, on the three parallel lines of Pico, 

 St. Jorge, and Terceira. Believing that a mountain- 

 axis differs essentially from a volcano, only in plutonic 

 rocks having been injected, instead of volcanic matter 

 having been ejected, this appears to me an interesting 

 circumstance ; for we may infer from it as probable, 

 that in the elevation of a mountain-chain, two or more 

 of the parallel lines forming it may be upraised and 

 injected within the same geological period. 



1 A similar conclusion is forced on us ; by the phenomena, which 

 accompanied the earthquake of 1835, at Conception, and which are 

 detailed in my paper (vol. v. p. 601) in the ' Geological Transactions.' 



