March, 1835. direction of vibration. 375 



other. Captain FitzRoy* has Ukewise remarked, that the 

 greater number of the masses of brickwork were thrown 

 down towards the N.E. Both these circumstances per- 

 fectly agree with the general idea of the undulation having 

 come from the S.W. ; in which quarter subterranean noises 

 were also sometimes heard. It is evident on this suppo- 

 sition, that the N.W. and S. E. walls, being nearly coin- 

 cident with the hne of undulation (or wdth the crests of 

 the successive waves), would be much more likely to fall 

 than those which had their extremities presented towards 

 the point whence the vibration proceeded ; for, in the first 

 case, the whole wall would be thrown at the same moment 

 out of its perpendicular. This may be illustrated by placing 

 books edgewise 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 to their direction. The fissures in 

 the ground, though not uniform, generally had a S.E. and 

 N.W. direction 5 1 and therefore they corresponded to the 

 lines of principal flexure. Bearing in mind all these cir- 

 cumstances, 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,t situated in that quarter, was during the 

 general uplifting of the land (to which I shall presently 

 refer) raised to nearly three times the altitude of any other 

 part of the coast. 



The different resistance offered by the walls, according to 

 their direction, was well exemplified in the case of the cathe- 

 dral. 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 dimensions ; and 

 they had been rolled to a distance on the level plaza, like 

 fragments of rock round the base of some high moun- 



* Sketch of Surveying Voyages of Adventure and Beagle by Captain 

 FitzRoy, Royal Geography Journal, vol. vi., p. 320. 

 f Ditto, p. 327, ft j)assim. 



