STKUCTURE AND ACTION OF VOLCANOS. 361 



of St. Vincent, in the neighbouring islands of the Antilles- 

 A remarkable phenomenon accompanied this eruption : at the 

 moment of this explosion, which occurred on the 30th of April, 

 1 8 1 1 , a terrible subterranean noise was heard in South America, 

 over a district of more than 35,000 square miles. The inha- 

 bitants of the banks of the Apure, at the confluence of the Rio 

 Nula, and those living on the remote sea-coast of Venezuela, 

 agreed in comparing this sound to the noise of heavy artillery. 

 The distance from the confluence of the Rio Nula with the 

 Apure (by which I entered the Orinoco) to the volcano of St. 

 Vincent, measured in a straight line, is no less than 628 miles. 

 This noise was certainly not propagated through the air, and 

 must have arisen from some deep-seated subterranean cause ; 

 its intensity was, moreover, hardly greater on the shores of 

 the Caribbean sea, near the seat of the raging volcano, than in 

 the interior of the country in the basin of the Apure and the 

 Orinoco. 



It would be useless to multiply examples of this nature, 

 by adducing others which I have collected: I will therefore 

 only refer to one further instance, namely, the memorable 

 earthquake of Lisbon, an important phenomenon in the annals 

 of Europe. Simultaneously with this event, which took 

 place on the 1st of November, 1755, not only were the Lakes 

 of Switzerland and the sea off the Swedish coasts violently 

 agitated, but in the eastern portion of the Antilles, near the 

 islands of Martinique, Antigua, and Barbadoes, the tide, 

 which never exceeds thirty inches, suddenly rose upwards of 

 twenty feet. All these phenomena prove, that subterranean 

 forces are manifested either dynamically, expansively, and 

 attended by commotion, in earthquakes ; or possess the property 

 of producing, or of chemically modifying substances in volca- 

 nos ; and they further show, that these forces are not seated 

 near the surface in the thin crust of the earth, but deep in the 

 interior of our planet, whence through fissures and unfilled 

 veins they act simultaneously at widely distant points of the 

 earth's surface. 



