214 Professor HofFmann on the Geological Investigations 



in the deep ravines of Palma. Buch first directed attention 

 to the fact, that the colossal cone of the PeaJc of TenerifFe is 

 surrounded, at a height of 7000 feet above the level of the 

 sea, by a magnificent amphitheatre of volcanic rocks of older 

 formation, in the midst of which the majestic cone, composed 

 of pumice and obsidian, was not elevated till a later period. 

 As to Lancerote, we have presented to us a grand and asto- 

 nishing picture of the gigantic operations which in 1730 pro- 

 duced one of the greatest known eruptions, an eruption that 

 covered several German square miles* of country continuously 

 with lava. 



Islands of Elevation. — But Buch proceeded much further 

 in his investigations respecting the influence .of volcanos on 

 the form of the surface of the earth, and thus enriched science 

 with a multitude of remarkable facts. From an ingenious 

 comparison of the best data, he deduced the conclusion, that 

 all the innumerable islands scattered throughout the oceanic 

 regions of the globe, such, for example, as the Canaries, are 

 of volcanic origin. He not only triumphantly overthrew the 

 opinion which had been so frequently brought forward, that 

 the groups of islands in the South Sea are the remains of a 

 sunken continent, whose former mountain summits now re- 

 main uncovered and insulated, but he also shewed that all 

 these islands are formed in a similar and peculiar manner, in- 

 asmuch as they all possess in their centre a funnel-shaped 

 cavity, whose bounding walls consist of the terminations of 

 the strata of the stony layers which rise up uniformly and cir- 

 cularly from the edges of the coast. This circumference is 

 broken up by numerous perpendicular, narrow, "^radiating, fis- 

 sure-like valleys ; and, in the interior of the great central 

 cavity, a new volcano has been formed, and individual erup- 

 tions have taken place through the walls. This peculiar ar- 

 rangement, these circularly ascending strata, these fissures, 

 and the hollow in the centre, are the consequences of an ele- 

 vation which took place prior to the outbreak of the volcano. 

 The now-inclined layers of lava, volcanic tufa, and conglome- 

 rate, were at one time horizontally disposed on the ancient 

 bed of the sea, and have been subsequently driven upwards 



^ A German mile s=s 4§ English. 



