Notice of Active and Extinct Volcanos. 287 



have been derived by successive changes from the fundamental 

 granite. Lowest of all Von Buch descried the primitive rocks ; 

 then masses of trachyte ; afterwards an aggregate consisting of 

 angular fragments of the latter rock, forming either a conglome- 

 rate or a tuff, which alternate with one another several succes- 

 sive times ; still higher an augite rock (dolerite) with felspar, 

 interstratified with beds of rolled masses of the same composi- 

 tion, but of a cellular structure ; then an amygdaloid ; and last 

 of all basalt." 



Lanzerote has a similar structure, and had evidently a sim- 

 ilar origin, but it has been since augmented by eruptions of 

 volcanic matter upon its surface. It is unlike the other isl- 

 ands of this group, flat, without abrupt cones and lofty preci- 

 pices, and with only one vestige of a crater, like those in Pal- 

 ma and the Grand Canary. Still there have been in this isl- 

 and, within the records of history, terrific and devastating- 

 eruptions, particularly in the year 1730. 



" After a painful walk, (says Von Buch,) over a tract of harsh, 

 undecomposed lava, I reached at length an eminence composed 

 entirely of an accumulation of slag and lapilli, which were heap- 

 ed in successive layers upon each other. In the centre was a 

 crater walled in by precipitous rocks, of which one side was 

 broken away by a lava which had proceeded from its interior. 

 Within the compass of this hollow two other minor craters ap- 

 pear, which emitted at the time volumes of aqueous vapour mix- 

 ed with sulphureous exhalations. Hence it is that the hill has 

 obtained the name of Montagna di Fuego. 



" It is impossible, continues Von Buch, to describe the scene 

 of desolation, which presents itself from the summit of this cra- 

 ter. A surface of more than three square miles in a westerly 

 direction is covered with black lava, in the whole of which space 

 nothing occurs to break the uniformity of the prospect, but oc- 

 casional small cones of basalt scattered over the plain. 



" It is clear that this vast mass of lava is not derived from any 

 one point ; even the Montagna di Fuego appearing to have con- 

 tributed but little to its formation, for the lava actually procee- 

 ding from the latter is found to take an easterly instead of a wes- 

 terly direction. During my ascent, I felt very anxious to as- 

 certain, what the other sources might be which assisted in emit- 

 ting so vast a mass of lava. How much was I astonished, when 

 on reaching the summit I perceived an entire series of cones, all 

 nearly as lofty as the Montagna di Fuego, placed so exactly in a 

 line, that the nearest covered the farther ones in such a manner, 

 that their summits alone were seen peeping from behind. 



