

ON ITS EXTERIOR. EARTHQUAKES. 201 



New Madrid in 1812; noxious gases which injured the herds 

 of cattle grazing on the chain of the Andes ; mud, black 

 smoke, and even flames, at Messina in 1783, and at Cumana 

 on the 14th Nov. 1797. During the great earthquake of 

 Lisbon (1st Nov. 1755), flames and a column of smoke 

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

 Alvidras, and the smoke was more dense as the subterranean 

 noise became louder. ( 191 ) At the destruction of Riobamba 

 (1797), where the shocks were not accompanied by any erup- 

 tion of the closely adjacent volcano, a singular mass (called 

 by the natives Moya), in which carbon, crystals of augite, 

 and siliceous shells of infusoria were intermingled, was pushed 

 up in numerous small conical eminences. During the 

 earthquake of New Granada (16th Nov. 1827), carbonic 

 acid gas issuing from fissures in the valley of the Magdalena 

 Eiver suffocated many snakes, rats, and other animals which 

 live in holes. Great earthquakes have sometimes been 

 followed in Quito and Peru by sudden changes in the 

 weather, and by a premature commencement- of the tropical 

 rainy season. Do gaseous fluids issue from the interior of 

 the earth and mingle with the atmosphere? or are these 

 meteorological processes the effects of a disturbance of the 

 electricity of the atmosphere by the earthquake ? In inter- 

 tropical parts of America, where sometimes, for ten months 

 together, not a drop of rain falls, repeated earthquake shocks, 

 which do no injury to the low reed-huts of the natives, are 

 regarded by them as the welcome harbingers of abundant 

 rain and a fruitful season. 



The common origin of the different phenomena which have 

 been thus described, is still wrapped in obscurity. Elastic 

 fluids subjected to enormous pressure in the interior of the 



