EARTHaUAKES. 213 



♦roni south to north "was very striking in the almost uninter- 

 rupted undulations of the soil in the alluvial valleys of the Mis- 

 sissippi, the Arkansas, and the Ohio, from 1811 to 1813. It 

 seemed here as if subterranean obstacles were gradually over- 

 come, and that the way being once opened, the undulatory 

 movement could be freely propagated. 



Although earthquakes appear at first sight to be simply dy- 

 namic phenomena of motion, we yet discover, from well-at- 

 tested facts, that they are not only able to elevate a whole dis- 

 trict above its ancient level (as, for instance, the Ulla Bund, 

 after the earthquake of Cutch, in June, 1819, east of the 

 Delta of the Indus, or the coast of Chili, in November, 1822), 

 but we also find that various substances have been ejected dur- 

 ing the earthquake, as hot water at Catania in 1818 ; hot 

 steam at New Madrid, in the Valley of the Mississippi, in 

 1812 ; irrespirable gases, Mofettes, which injured the flocks 

 grazing in the chain of the Andes ; mud, black smoke, and 

 even flames, at Messina in 1781, and at Cum ana on the 14th 

 of November, 1797. During the great earthquake of Lisbon, 

 on the 1st of November, 1755, flames and columns of smoke 

 were seen to rise from a newly-formed fissure in the rock of 

 Alvidras, near the city. The smoke in this case became more 

 dense as the subterranean noise increased in intensity. =^ At 

 the destruction of Riobamba, in the year 1797, when the 

 shocks were not attended by any outbreak of the neighboring 

 volcano, a singular mass called the Moya was uplifted from 

 the earth in numerous continuous conical elevations, the whole 

 being composed of carbon, crystals of augite, and the silicious 

 shields of infusoria. The eruption of carbonic acid gas from 

 fissures in the Valley of the Magdalene, during the earthquake 

 of New Granada, on the 16th of November, 1827, sufibcated 

 many snakes, rats, and other animals. Sudden changes of 

 weather, as the occurrence of the rainy season in the tropics, 

 at an unusual period of the year, have sometimes succeeded 

 violent earthquakes in Quito and Peru. Do gaseous fluids rise 

 from the interior of the earth, and mix with the atmosphere % 

 or are these meteorological processes the action of atmospheric 

 electricity disturbed by the earthquake ] In the tropical re- 

 gions of America, where sometimes not a drop of rain falls for 

 ten months together, the natives consider the repeated shocks 

 of earthquakes, which do not endanger the low reed huts, as 

 auspicious harbingers of fruitfulness and abundant rain. 



* Philos. Transact., vol. xlix., p. 414. 



