ABOUT VOLCANOS AND EARTHQUAKES. 37 



one of the Sandwich Isles, exhibits the remarkable 

 phsenomenon of a lake of molten and very liquid lava 

 always filling the bottom of the crater, and always in a 

 state of terrific ebullition : rolling to and fro its fiery 

 surge and flaming billows yet with this it is content, 

 for it would seem that at least for a long time past there 

 has been no violent outbreak so as to make what is 

 generally understood by a volcanic eruption. Volcanic 

 eruptions are almost always preceded by earthquakes, by 

 which the beds of rock, that overlie and keep down the 

 struggling powers beneath, are dislocated and cracked, 

 till at last they give way, and the strain is immediately 

 relieved. It is chiefly when this does not happen, when 

 the force below is sufficient to heave up and shake the 

 earth, but not to burst open the crust, and give vent to 

 the lava and gases, that the most destructive effects are 

 produced. The great earthquake of November i, 1755, 

 which destroyed Lisbon, was an instance of this kind, 

 and was one of the greatest, if not the very greatest on 

 record ; for the concussion extended over all Spain and 

 Portugal indeed, over all Europe, and even into Scot- 

 land over North Africa, where in one town in Morocco 

 8000 or 10,000 people perished. Nay, its effects 

 extended even across the Atlantic to Madeira, where it 

 was very violent ; and to the West Indies. The most 

 striking feature about this earthquake was its extreme 

 suddenness. All was going on quite as usual in Lisbon 

 the morning of that memorable day ; the weather fine 

 and clear ; and nothing whatever to give the population 

 of that great capital the least suspicion of mischief. All 



