132 ' EARTHQUAKES. 



* Humboldt observed that the Cordilleras, composed of 

 gneiss and mica- slate, and the country immediately at 

 their foot, were more shaken than the plains/^ 



'Some writers have asserted that the wave- like move- 

 ments (of the Calabrian earthquake in 1783) which were 

 propagated through recent strata from west to east, became 

 very violent when they reached the point of junction with 

 the granite, as if a reaction was produced when the undula- 

 tory movement of the soft strata was suddenly arrested by 

 the more solid rocks.' 



Dolomieu when speaking of this earthquake says, the 

 usual effect ' was to disconnect from the sides of the 

 Apennines all those masses (of sand and clay) which 

 either had not sufficient bases for their bulk, or which 

 were supported only by lateral adherence.' 



These intensified actions taking place at and near to 

 lines of junction between dissimilar strata is probably due 

 to the phenomena of reflection and refraction. 



When referring to the question as to whether build- 

 ings situated on loose materials suffered more or less than 

 those on solid rocks. Mallet, in his description of the 

 Neapolitan earthquake of 1857, remarks: 'We have in 

 this earthquake, towns such as Saponara and Viggiano, 

 situated upon solid limestone, totally prostrated ; and we 

 have others such as Montemarro, to a great extent based 

 upon loose clays, totally levelled. We have examples of 

 almost complete immunity in places on plains of deep 

 clay as that of Viscolione, and in places on solid lime- 

 stone, like Castelluccio, or perched on mountain tops like 

 Petica.' ■ 



After reading the above, we see that the probable reason 

 why, in several cases, beds of soft materials have not made 



1 Principles of Geology, Lyell, vol. ii. p. 106. 



8 The Keajmlitan Earihqnalte of 1857, R. Mallet, vol. ii. p. 359. 



