§ 4. EARTHQUAKE OF LISBON. 809 



4. Earthquake of Lisbon. — The earthquake of Lisbon, 

 in 1775, which suddenly destroyed 60,000 persons, was the 

 most extensively felt of any on record. Its effects were 

 perceived over the whole of Europe, the North of Africa, 

 and in the West Indies : and it is computed that a portion 

 of the earth's surface four times the extent of Europe was 

 simultaneously affected. The enormous undulations of the 

 sea by which it was followed, and that swept along the 

 coasts of Spain, Portugal, and Africa, are supposed to have 

 arisen from the sudden upheaval or subsidence of a vast area 

 of the bed of the Atlantic Ocean, beneath which the prin- 

 cipal focus of the subterranean disturbance appeared to be 

 situated. The effects of this earthquake were felt in many 

 parts of England, Scotland, and Ireland, and even as far as 

 Norway ; and the waves occasioned by the concussion 

 reached our southern shores, and the waters of Loch 

 Ness, and of other inland lakes, were simultaneously agi- 

 tated. Even the thermal springs of countries remote from 

 the catastrophe were affected : those at Toplitz in Bohemia, 

 which for centuries had flowed in a pure and equal stream, 

 suddenly ceased, and then burst forth in a flood of turbid 

 water of a very high temperature. 



Humboldt remarks, that it is probable the earth's surface 

 is always disturbed at some one point, and that it is inces- 

 santly affected by the reaction of the interior against the 

 exterior. The permanent elevation of extensive tracts by 

 earthquakes sometimes takes place ; as on the coast of Chili, 

 in 1822 (ante, p. 112); and they are often accompanied 

 with eruptions of mud, steam, hot water, carbonic acid gas, 

 and other elastic fluids. 



The present grand European centre of volcanic action is 

 in Southern Italy, which has for ages been in a state of 

 energy ; Etna, Vesuvius, and the Lipari Isles, being the 

 vents through which the incandescent materials have 

 escaped. 



