286 Notice of Active and Extinct Volcanos. 



islands of this group, " the strata seem to have been elevated 

 from the bottom of the ocean, by the force of elastic vapors ; 

 for they dip away in all directions from some central point, 

 where a crater still exists to attest the former agency of elastic 

 fluids." 



" The beds are all intersected by dykes of granular basalt, 

 which become more and more abundant as we proceed along the 

 valley, until, at length the lofty wall of rock which bounds it, is 

 covered with a net work of them. 



" These beds all rise towards the crater, or, as it is called by 

 the people, the great Caldera, a circular opening in the centre 

 of the island, the depth of which is stated by Von Buch as ex- 

 ceeding five thousand feet. From its brim we are enabled to 

 look down upon the abyss, and observe underneath us the ter- 

 minations of the strata, which we have successively passed in 

 our way to it. Viewed from this point they all appear horizon- 

 tal, but this, as I observed in speaking of the Monte Somma, is 

 an illusion, and arises from their terminations only being visible, 

 and from their ranging at an equal elevation in every part of the 

 circular wall, which bounds the internal cavity of the crater. 



" The caldera of the Isle of Palma, says Von Buch, differs 

 much from the crater of an ordinary volcano. Here are no 

 streams of lava, no slags, no rapilli or ashes. Nor do we ever 

 find the latter of such a circumference, or so profound and ab- 

 rupt. Its general aspect seems to shew that it was formed by the 

 pressure of those elastic fluids which raised the whole island 

 above the level of the ocean, and changed the strata composing 

 it from an horizontal to their present highly inclined position." 



" Considering therefore that the crater in this instance is unat- 

 tended with the usual phenomena of a volcano, and is even dis- 

 tinguished from the latter by the preceding characters, Von 

 Buch has chosen to denote it by the name of " Erhebungs cra- 

 ter" or crater of elevation, and he proceeds to shew that the 

 same distinctive title is applicable to many craters both among 

 these islands and in other parts of the globe." 



The Great Canary has a structure very similar to that of 

 Palma; "the same heaving up of the strata round a central 

 point, the same deep and abrupt vallies, (called barancas,) 

 the same description of crater, exhibiting the successive out 

 crops of the adjoining beds." 



" The order of superposition in the latter is such as to illus- 

 trate apparently the gradation that often occurs in the character 

 of volcanic products, and perhaps the manner in which they 



