118 EARTHQUAKES IN THE EIGHTEENTH CENTUEY. [Ch. XXIX. 



others ; and disputes arose as to whom the property which 

 had thus shifted its place should belong. 



From this account of Dolomieu we might anticipate, as 

 the result of a continuance of such earthquakes first a 

 longitudinal valley following the line of junction of the older 

 and newer rocks ; secondly, greater disturbance in the newer 

 strata near the point of contact than at a greater distance 



from the mountains ; 



lienomena very common in other 



parts of Italy at the junction of the Apennine and Sub- 

 apennine formations. 



om 



Mr. Mallet, in his valuable essay on the Dynamics of 

 Earthquakes,"^ offers the following explanation of the fact to 

 which Dolomieu has called attention. When a wave of 

 elastic compression, of which he considers the earth-wave to 



an extremely 



low elasticity, such as clay and gravel, into another like 

 granite, whose elasticity is remarkably high, it changes not 

 only its velocity but in part also its course, a portion being 

 reflected and a portion refracted. The wave being thus sent 

 back again produces a shock in the opposite direction, doing 

 great damage to buildings on the surface by thus returning 

 upon itself. At the same time, the shocks are at once eased 

 when they get into the more elastic materials of the granitic 

 mountains. 



The surface of the countrv duringr the Calabrian earth- 

 quakes often heaved like the billows of a swelling sea, which 

 produced a swimming in the head, like sea-sickness. It is 

 particularly stated, in almost all the accounts, that just 

 before each shock the clouds appeared motionless; and, 

 although no explanation is offered of this phenomenon, it 

 seems obviously the same as that observed in a ship at sea 

 Avhen it pitches violeutly. The clouds seem arrested in their 

 career as often as the vessel rises in a direction contrary to 

 their course ; so that the Calabrian s must have experienced 

 precisely the same motion on the land. 



Trees, supported by their trunks, sometimes bent 'during 

 the shocks to the earth, and touched it with their tops. This 



\ 



* Proceed. Eoy. Irish Acad. 1816, p. 26. 



