LINES OF VIBRATION. 53 



perpendicular; for the undulations, coming from 

 the S.W., must have extended in N.W. and S.E. 

 waves, as they passed under the foundations. This 

 may be illustrated by placing books edgeways on 

 a carpet, and then, after the manner suggested by 

 Michell, imitating the undulations of an earthquake : 

 it will be found that they fall with more or less 

 readiness, according as their direction more or less 

 nearly conincides with the line of the waves. The 

 fissures in the ground generally, though not uni- 

 formly, extended in a S.E. and N.W. direction, 

 and therefore corresponded to the lines of undula- 

 tion, or of principal flexure. Bearing in mind all 

 these circumstances, which so clearly point to the 

 S.W. as the chief focus of disturbance, it is a very 

 interesting fact that the island of S. Maria, situated 

 in that quarter, was, during the general uplifting 

 of the land, raised to nearly three times the height 

 of any other part of the coast. 



The difterent resistance offered by the walls, ac- 

 cording to their direction, was well exemplified in 

 the case of the Cathedral. The side which fronted 

 the N.E. presented a grand pile of ruins, in the 

 midst of which door-cases and masses of timber 

 stood up, as if floating in a stream. Some of the 

 angular blocks of brickwork were of great dimen- 

 sions, and they were rolled to a distance on the 

 level plaza, like fragments of rock at the base of 

 some high luountain. The side walls (running 

 S.W. and N.E.), though exceedingly fractured, yet 

 remained standing; but the vast buttresses (at right 

 angles to them, and therefore parallel to the walls 

 that fell) were in many cases cut clean off", as if by 

 a chisel, and hurled to the ground. Some square 

 ornaments, on the coping of these same walls, were 

 moved by the earthquake into a diagonal position. 

 A similar circumstance was observed after an earth- 

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