VOLCANIC PHENOMENACRATERS. 109 



hollow in the centre, and cracked on the margin. This must have taken 

 place in many cases, and notably in the mass of Etna, (,fig. 192), the east- 

 ern slope of which presents a vast excavation, called Vtd del Bove, which is 

 bounded by high ridges, cracked at various points. 



Lava of 1822. - 



Terminal cone. " 

 Va) de Bove. 



Lava of 1CC9. 



CATANEA. - -^^ 



i 



Islands of Cyclops '-; 



Fig. 192. Plan of Etna and its environs, according to the relievo of 

 M. Elie de Beaumont. 



This comment need not he regarded as a simple theoretic speculation 

 there are many examples of similar excavations, independent of the effects 

 produced by earthquakes. At the summit of Mount Etna there is one of 

 1300 feet in depth, which dates from 1832, and many others which were 

 produced at the end of the last or beginning of the present century. Fre- 

 quently lakes are formed on a sudden, sometimes of boiling water, by the 

 sinking of the land consequent on volcanic eruptions, as in 1835, near the 

 ancient Cesarea in Cappadocia; in 1820, in St. Michael's (Azores), &c. It 

 has also happened that high volcanic mountains have at once sunk, their 

 place being at once filled by deep lakes, as the volcano of Papadayann in 

 Java, in 1772, which carried away with it forty villages built on its sides 

 as also, in 1638, the peak of the Moluccas, which could be perceived twelve 

 leagues at sea. We know that the summit of Cargu.irai'zo which rivalled 

 Ohimborazo in height, crumbled in 1 698, and the same occurred to Capac- 

 TJrcu, also situited on the plane of Quito, a short time before the arrival of 

 the Spaniards in America. Many other facts of 4^Bimilar kind could be 

 adduced in support of the theory advanced. 



17. Effects subsequent to elevation. The crate 'riform cavities 

 we have spoken of sometimes remain the same as when first pro- 

 duced ; often, however, various volcanic phenomena subsequently 

 occur at different times and in various ways. In this manner it 

 was that the cone of Vesuvius (fig. 185) was formed in 79 in the 

 ancient crater of the Somma (p. 104) ; that the peak of TenerifFe 

 is found in a circle, the vertical walls of which rise from 600 to 

 1200 feet; that the volcan of Taal, in Luzon, one of the Philip- 

 pine islands, is in the centre of a basin filled with water, and our 



17. Do craters of elevation always remain the same as when first pro 

 duced ? Give some examples of the secondary effects of eruption*. 



10 



