EARTHQUAKES. 209 



south to north was very striking in the almost uninterrupted 

 undulations of the soil in the alluvial valleys of the Mississippi, 

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

 here as if subterranean obstacles were gradually overcome, and 

 that the way being once opened, the undulatory movement 

 could be freely propagated. 



Although earthquakes appear at first sight to be simply 

 dynamic phenomena of motion, we yet discover, from well 

 attested facts, that they are not only able to elevate a whole 

 district 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 

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

 hot steam at New Madrid, in the valley of the Missis- 

 sippi, 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 Cumana, 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 neighbouring volcano, a singular mass called the Moya was 

 uplifted from the Earth in numerous continuous conical ele- 

 vations, 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 Grenada, on the 1 6th of No- 

 vember, 1827, suffocated 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 xise from the interior of the Earth and mix 

 with the atmosphere ? or are these meteorological processes 

 the action of atmospheric electricity disturbed by the earth- 

 quake ? In the tropical regions of America, where sometimes 



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



P 



