OF THE EARTH'S SURFACE. 151 



In the Philosophical Transactions, vol. xlix. p. 424. we 

 have an account of the earthquake at Cadiz, by Mr B. Be- 

 wicke, merchant there, 1st November 1755, in which it is said, 

 " an hour after" (the first shock) " looking out to sea, we saw a 

 " wave coming, at eight miles distance, which was at least six- 

 " ty feet higher than common. Every body began to tremble ; 

 " the centinels left their posts, as well they did; it came 

 ** against the west part of the town, which is very rocky ; the 

 " rocks abated a great deal of its force; at last it came upon 

 " the walls, and beat in the breast-work, and carried pieces of 

 " eight or ten tons weight, forty or fifty yards from the walls,'* 

 &c. 



We have another account of the same by Don Antonio de 

 Ulloa, Phil. Trans, vol. xlix. p. 427. who describes the wave 

 as having returned five times after the first *. And similar 

 facts are stated of other scenes of this sort. 



One circumstance in addition to those mentioned, which has 

 accompanied all these great events, and which seems at first 

 sight to contradict our explanation of them is, that in all the 

 agitations of the water, the first event has been a retreat of the 

 sea. 



Mr 



* He says, " the inhabitants had scarcely begun to recover from their first 

 ** terror, when they saw themselves plunged into new alarms ; at ten minutes 

 " past eleven, they saw, rolling towards the city, a tide of the sea, which passed 

 " over the parapet of sixty feet, above the ordinary level of the water ; at thirty 

 " minutes past eleven came a second tide, and these two were followed by four 

 " others of the same kind, at fifty minutes past eleven ; at twelve o'clock, thirty 

 " minutes ; one o'clock, ten minutes ; one o'clock, fifty minutes. The tides 

 " continued, with some intervals, till the evening, but lessening. They have 

 « ruined one hundred toises of the rampart, part of which, of three toises length, 

 " and of their whole thickness, were carried by the torrent fifty paces." It is 

 remarkable, that in these six waves, the two first intervals of time are exactly of 

 twenty minutes each, and the three others of forty. It is probable, that they 

 have all resulted from one great impulse. 



