46 Natural History of Volcanos and Earthquakes. 



casionally been witnessed, may be satisfactorily explained by the 

 rising of steam and gases, which may have the effect either of 

 heating the water, or of throwing out solid bodies.* The same 

 may be said of the concussions of the earth which take place, 

 sometimes in horizontal undulations, sometimes in vertical shocks, 

 and sometimes with a vibratory motion, backwards and forwards. 

 The latter of these convulsions, called by the Neapolitans, moto 

 vorticoso, is most common during the greatest earthquakes. 



Von Humboldt has proved, by abundant examples, that the 

 propagation of earthquakes is not confined to any particular rock, 

 but that the most varied formations are equally favorable to it. 

 We infer, therefore, that the seat of earthquakes must be below 

 all known rocks. Although all the rocks may be agitated, yet 

 the manner of extension of the shocks in them is different, ac- 

 cording to their particular quality. The earthquakes, which 



the 21st October 1766, which totally destroyed the city of Cumana, the earth 

 opened at several places in the province, and vomited sulphureous water. These 

 eruptions were particularly numerous in a plain, which extends towards Casanay 

 two geographical miles eastward of Cariaco, and which is known by the name of 

 the hollow land {tierra hueca) because it seems to be every where undermined by 

 hot springs. Von Humboldt, Reise, t. i, p. 482. During the violent earthquake, 

 which in one minute overthrew the city of Caraccas, on the 26th March 1813, so 

 much water was thrown up through the cracks, that a new' stream was formed. 

 At the same time the ground was also found covered with a fine white earth, like 

 volcanic ashes, which had been thrown up from fissures in the neighborhood. The 

 eruptions of volcanic masses were still more considerable during the earthquake 

 of Rlohamha, 1797. The earth was fissured at innumerable places, and immense 

 gulfs were formed in some places. Masses of water rose, filling up valleys 1000 

 ft. wide, and 600 ft. in depth ; and also at the same time a peculiarly stinking mud, 

 consisting of volcanic matter, accumulated so as to form considerable hills, now 

 called moya. Wide rents were likewise opened during the violent earthquake in 

 the north coasts of Soiith America, last year, in order to give exit to streams of 

 water which rose. It was often observed, that during the earthquakes, water 

 with sand, mud, &c., was thrown up from wells, sometimes to a height of 30 ft. 

 Von Humboldt relates, (Relat. Hist., t. ii, p. 287,) that this phenomenon is gen- 

 erally observed during the earthquakes at Cumana. The same thing happened 

 the 1st Nov. 1755 near Colares, (Philos. Trans, t. xlix, p. 416,) and also during 

 the earthquake in Calabria. (Journ. de Phys. Ixii, p. 263.) 



* Thus, during the above-mentioned earthquake on the north coast of Soiit/i 

 America, columns of smoke were seen rising out of the sea, a league from the 

 shore, and in a depth of about 210 ft.; and in the night, flames were seen issuing 

 from the same spot, which illuminated all the coasts of the island. Afler each 

 shock, the sea retired, left the sliips which were in the bay aground, and laid bare 

 the rocks to a great depth; the waves at tlie same time ran to a height of 16 ft. to 

 20 ft. During the shocks the earth opened and closed again very rapidly. When 



