Masterpieces of Science 



present time, and forms the semi-circular hill 

 known as Monte Somma. Fig. 56 is a view of 

 Vesuvius half encircled by the cliffs of this 

 ancient crater. 



When a volcano is situated near the coast and 

 by far the larger number of existing volcanoes 

 are so situated the ashes may be showered into 

 the sea, or be borne thither by the wind, and 

 may, in this way, get mixed with the detrital 

 matter which is spread over the sea-bottom. 

 A curious series of deposits may thus be produced 



Fig. 56. Vesuvius and Monte Somma 



consisting partly of materials worn away from 

 the land by the action of the water, and partly 

 of matter ejected from subterranean sources. 

 In some cases, volcanic outbreaks take place 

 actually beneath the sea, and the matter thrown 

 up becomes mixed with the remains of shell-fish 

 and other marine organisms. Submarine vol- 

 canoes occasionally give rise to new land, the 

 erupted matter being piled up in sufficient quan- 

 tity to form an island rising above the waters. 

 Thus in the year 1831 an island, which Admiral 

 Smyth named Graham Island (Fig. 57) appeared 

 186 



