ABOUT VOLCANOS AND EARTHQUAKES. 43 



pletely disappeared.* In numerous other instances, the 

 cones of cinders and scoriae, once raised, have become 

 compacted and bound together by the effusion of lava, 

 hardening into soHd stone, and thus, becoming habitual 

 volcanic vents, they continue to increase in height and 

 diameter, and assume the importance of permanent vol- 

 canic islands. Such has been, doubtless, the history of 

 those numerous msular volcanos which dot the ocean 

 in so many parts of the world, such as Teneriffe, the 

 Azores, Ascension, St Helena, Tristan d'Acunha, etc. 

 In some cases the process has been witnessed from its 

 commencement, as in that of two islands which arose in 

 the Aleutian group, connecting Kamtschatka with North 

 America, the one in 1796, the other in 1814, and which 

 both attained the elevation of 3000 feet. 



(56.) Besides these evident instances of eruptive action, 

 there is every reason to believe that enormous floods of 

 lava have been, at various remote periods in the earth's 

 history, poured forth at the bottom of seas so deep as to 

 repress, by the mere weight of water, all outbreak ol 

 steam, gas, or ashes ; and reposing perhaps for ages in a 

 liquid state, protected from the cooling action of the 

 water on their upper surface by a thick crust of con- 

 gealed stony matter, to have assumed a perfect level; and, 

 at length, by slow cooling, taken on that peculiar colum- 

 nar structure which we see produced in mmiature in 



* Such an event is at this moment in progress (March 1866), 

 close to the island of Santorini, in the bay of Thera. ir. the Greek 

 Archipelaj^^o : itself, with the adjacent Kaimeni Islands, products ol 

 the same kind. 



