200 REACTION OF THE INTERIOR OF THE EARTH 



cavities favour the propagation of the undulations moving 

 in their own direction ; sometimes, however, the waves 

 intersect several chains almost at right angles ; an example 

 of which occurs in South America, where they cross both the 

 littoral chain of Venezuela and the Sierra Parime. In Asia 

 shocks of earthquakes have been propagated from Lahore and 

 the foot of the Himalaya (22d Jan. 1832), across the chain of 

 the Hindoo Coosh, as far as Badakschan, or the upper Oxus, 

 and even to Bokhara. ( 19 ) The range of the undulations is 

 sometimes permanently extended, and this may be a conse- 

 quence of a single earthquake of unusual violence. Since 

 the destruction of Cumana on the 14th Dec. 1797, and only 

 since that epoch, every shock on the southern coast extends 

 to the mica slate rocks of the peninsula of Maniquarez, 

 situated opposite the chalk hills of the main land. In the 

 great alluvial vallies of the Mississipi, the Arkansas, and the 

 Ohio, the progressive advance from south to north of the 

 almost uninterrupted undulations of the ground between 1811 

 to 1813, was very striking. It would seem as if subterranean 

 obstacles were gradually overcome ; and that the way being 

 once opened, the undulatory movement is propagated through 

 it on each occasion. 



If earthquakes appear at first sight to produce solely dy- 

 namical effects, we learn on the other hand, from well- 

 established evidence, that not only are whole districts of 

 country elevated by them above their former level (such as 

 the UUa-Bund, east of the Delta of the Indus, after the 

 earthquake of Cutch in June 1819, rand the coast of Chili 

 in November 1822) but also that during their occurrence va- 

 rious substances are ejected from the earth; such as hot-water 

 at Catania in 1818; hot steam in the Valley of the Mississipi at 



