DYNAMICAL GEOLOGY. 263 



with water-substance, and brought to the surface in virtue of 

 the expansive force of escaping vapours and gases. 



Sir Charles Lyell held views very similar to those of 

 Poulett-Scrope. His observations in the Auvergne, and at 

 Vesuvius and Etna, had convinced him of the mistaken 

 principles in the Elevation-Crater theory. He made the 

 pertinent objection that one of the "craters of elevation" 

 mentioned by Von Buch was entirely composed of marine 

 or littoral sediments ; and he explained the enormous 

 "cauldrons" of Palma, Gran Canaria, Bourbon, etc., as 

 craters due to volcanic explosion ; and the circular walls of the 

 Somma, the Peak of Teneriffe, Etna, etc., as the remainder 

 of old crater walls. In common with Poulett-Scrope, Lyell 

 ascribed the conical form of most volcanoes to the accumu- 

 lation of volcanic products round a vent, and he accepted 

 Scrope's view that volcanic eruptions were originated by the 

 explosive disengagement of the compressed vapours and gases 

 from subterranean magma. His wider geological experience, 

 however, led him to the further conclusion that the water- 

 substance dissolved in the magma had been introduced into 

 it by percolation downward from the surface, and that the 

 characteristic occurrence of serial volcanoes on the sea-board 

 betokened direct influence of the sea-water upon the sub- 

 terranean magma. 



Dr. Charles Daubeny's Description of Active and Extinct 

 Volcanoes, etc. (1826), although less full of original matter 

 than the works of Scrope and Lyell on kindred subjects, 

 was distinguished by greater chemical and mineralogical 

 knowledge. His treatment of European volcanoes is based 

 for the most part on his own field investigations of the various 

 localities, and careful laboratory research of the volcanic rocks. 

 Daubeny was favourably inclined to Buch's "Elevation-Crater" 

 theory, and thought that Scrope attached too great importance 

 to the expansion of vapours, and too little importance to 

 chemical processes in his explanation of volcanic eruption. 



Valuable results of .a special study of the Lipari Islands 

 were made known in 1832-33 by Friedrich Hoffmann, but the 

 complete researches of this gifted writer were first published by 

 Von Dechen after Hoffmann's death, in Karsten's Archiv fur 

 Mineralogie, 1839. Hoffmann contended that there was no 

 essential difference in point of structure between the craters 

 attributed by Von Buch to crust-elevation and fissure, and the 



