THE CRUST OF THE EARTH. 



of the waters, and by the sudden elevation of the matter which 

 existed at the bottom of the sea. This took place in 1820 at the 

 island of Banda in the Moluccas, where the bay, which previously 

 had a depth of 50 fathoms, was elevated by the tranquil upheaving 

 of compact basaltic matter which previously existed there, and 

 which formed a promontory composed of large blocks piled one 

 upon the other, without any accessory phenomena except the 

 increased temperature of the waters. 



It has been ascertained also that violent submarine eruptions 

 are often followed by slow and gradual upheavings of the bottom 

 of the sea. This effect was manifested in the case of the island 

 near Unalaska, and also in those produced near Santorin. It may 

 be added also, that the islands thus produced are not always 

 permanent ; many of them disappear after intervals of more or 

 less duration, being either swept away by the water or sinking 

 into abysses formed under them. 



140. Yolcanic craters, which result from the upheaving of the 

 crust of the earth in places where no volcano previously existed, 

 are distinguished by the name of CEATERS OF ELEVATION, from 

 those craters which break out at different points in existing vol- 

 canoes. In like manner, the conical mounds similarly formed are 

 called cones of elevation. Craters of elevation are distinguishable 

 even in places where no record or tradition of eruption exists, by 

 the arrangement of the strata elevated, which is altogether dis- 

 similar from what is found elsewhere. These strata are always 

 inclined in all directions round the axis of the cone, as shown in 

 fig. 59, presenting their edges abruptly towards the centre of the 

 cavity. The Monte Nuovo, already mentioned, presents an example 

 of this upon a small scale. The same formation is presented in 

 the case of the semicircular Somma of Vesuvius. 



141. Another characteristic, not less important, and especially 



useful for geological purposes in 

 Fig. 59. cases where the matter elevated is 



not stratified, is supplied in all 

 great craters of elevation by the 

 crevasses which extend from the 

 borders of the crater to the external 



base of the mountain, and which are presented in so remarkable 

 a manner in the Canaries, where they are called Barancos. These 

 radiating crevasses are admirably shown upon the plan of the 

 island of Palma, one of the Canaries, drawn by M. de Buch. 



One of these Barancos, much deeper than the others, extends 

 from the foot of the mountain, at a place called Tazacorte, to the 

 base of the crater, as shown in the plan, and which is rendered 

 still more apparent in the perspective view shown in fig. 61. 

 106 



