1 98 



PHYSIOGRAPHY. 



[chap. 



of deposits may thus be produced, consisting partly of 

 materials -worn away from the land by the action of the 

 water, and partly of matter ejected from subterranean 



Fig. 56. — Vesuvius and Monte Somma, 



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 volcanoes occasionally give rise to 



r.,-.") 



Fig. 57.— Graham Island, 1831. 



new land, the erupted matter being piled up in sufficient 

 quantity to form an island rising above the waters. Thus, 

 in the year 183 1 an island, which Admiral Smyth named 



