THE CRUST OF THE EARTH. 



eruption, these cavities appear to have generally a conical form, 

 the base of the cone being presented upwards, and the lower part 

 filled with consolidated lava, by which the principal chimney of 

 the crater is covered. Sulphurous vapour is observed to issue 

 from its fissures and interstices, sometimes several open gulfs are 

 seen, from some of which vapours are emitted, and at the bottom 

 of others incandescent lava is seen. Others again are silent and 

 dark, and inspire an indescribable sense of terror. 



154. The crater Stromboli, which has been in activity since the 

 most ancient times, presents at present the same appearances as 

 those which were described by Spallanzani, in 1788. It is 

 constantly filled with lava in a state of fusion, which alternately 

 rises and falls in the cavity. Having ascended to ten or twelve 

 yards below the summit of the walls, this boiling fluid is covered 



'^m. 



}-:^M 



Fig. 67. Vesuvius in 1829. 



with large bubbles, which burst with noise, letting enormous 

 quantities of gas escape from them, and projecting on all sides 

 scoriaceous matter. After these explosions, it again subsides, 

 but only to rise again and produce like effects these alternations 

 being repeated regularly at intervals of some minutes. In craters 

 114 



