THE CRUST OF THE EARTH. 



thousand feet. The volcano of Taal, in the island of Lucon, one 

 of the Philippines, is placed in the centre of a basin filled with 



Fig. 64. Forms of volcanic islands. 



Fig. 65. 



water and surrounded by steep and elevated rocks, which leave a 

 single issue from it as in the cases already described. 



151. A similar example of this form is presented in the case of 

 Barren Island in the Bay of Bengal (fig. 66, p. 65), which consists 

 of a circle of high mountains, into which the sea flows through a 

 single opening, and of which the centre is occupied by a volcano 

 two thousand feet high, which was in full activity at the time 

 of the discovery of the island. 



152. The islands of Santorin and Theresia, already described, 

 form probably the borders of vast craters of elevation. Ancient 

 historians cite them as having appeared long before the Christian 

 era, after a succession of violent earthquake shocks, and in 

 accordance with this tradition, they present strata inclined out- 

 wards, as shown in fig. 67 ; the islands more recently elevated 



Fig. 07. 



having issued from the middle of the crater. The strata observed 

 in Santorin and Theresia, are inclined from the centre in accord- 

 ance with the principle explained in (140). 



112 



