Volcanos and EarthquaJces. 35S 



plained 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 takes place, sometimes in horizontal undulations, 

 sometimes in vertical shocks, and sometimes with a vibratory 

 motion, backwards and forwards. The latter of these convul- 

 sions, called by the Neapolitans, moto vortkoso, 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 favour- 

 able 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, according to their particular quality. The earth- 

 quakes, which have at different periods ravaged Smyrna^'f 

 Messina,\ Kwgstozvn in Jamaica 1792, the county of Pigne- 

 rol 1808,11 Calabria,^ Talcahuano in CMU^^^ &c. have always 

 had a greater effect on diluvium and alluvium, than on rocks. 

 Houses, for instance, built on sandy ground, were demolished, 

 while those which stood on rocks were but little damaged. 

 The shocks therefore act less violently and destructively on 

 solid and rocky ground than on loose soil, which is unable to 

 resist, and propagates the shock irregularly. In Calabria^ 

 where the loose soil occurred lying on granite on the declivity 



* Thus, during the above-mentioned earthquake on the north coast of S. 

 Amenca, 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. 

 After each shock, the sea retired, left the ships which wore in the bay 

 aground, and laid bare the rocks to a great depth ; the waves at the same 

 time ran to a height of 16 ft. to 20 ft. During the shocks the earth opened 

 and closed again very rapidly. When tranquillity was restored, a whirlpool 

 was observed in the sea, as if the waters were being swallowed up in an 

 immense gulf. The temperature of the sea in the bay was raised, and 

 bubbles of gas were seen rising all over the surface. 



t Hist, de I'Acad. des Sciences, an. 1688. Bufl^on Hist. Nat. t. i. p. 515. 



X Spallanzani, Voyage, t. iv. p. 138. 11 Joum. de Phys. t. Ixvii. p. 2.38. 



§ Oryktologische Bemerkungen iiber Calabrien &c., 1784. 



^ Nautical Magazine, Nos. 49 and 51, March and June 1836. 



