150 



EARTHQUAKE OF LISBON. 



[Ch. XXX 



when tlie first shock was felt at Lisbon, and its time of 



occurrence at several distant places."^ 



Great 



/ 



—A great wave swept 



over the coast of Spain, and is said to have been 60 feet hin-h 

 at Cadiz- At Tangier, in Africa, it rose and fell 18 times on 



the coast. 



Madeii 



r mark 



ebbs and flows there 7 feet, was then at half ebb. 



entering the 



city, and committing great havoc, it over- 

 flowed other seaports in the island. At Kinsale, in Ireland 

 a body of water rushed into the harbour, whirled round 

 several vessels, and poured into the market-place. 



It was before stated that the sea first retired at Lisbon • 



and this retreat of the 

 mencement of an eartl 



from the shore, at the corn- 



common 



In order to account 



Michell 



bottom of the sea, from the giving way of the roof of some 



vacuum 



sation of steam. Such condensation, he observes, might be 

 the first effect of the introduction of a large body of water 

 into fissures and cavities already filled with steam, before 

 there has been sufiicient time for the heat of the incandescent 

 lava to turn so large a supply of water into steam, which 

 being soon accomplished causes a greater explosion. 



Another proposed explanation is, the sudden rise of the 

 land, which would cause the sea to abandon immediately the 

 ancient line of coast ; and if the shore, 

 heaved up, should fall again to its original level, the ocean 

 would return. This theory, however, Avill not account for 

 the facts observed during the Lisbon earthquake ; for the 

 retreat preceded the wave, not only on the coast of Portugal, 

 but also at the island of Madeira, and several other places. 

 If the upheaving of the coast of Portugal had caused the 

 retreat, the motion of the waters, when propagated to 

 Madeira, would have produced a wave previous to the retreat. 



The shock transmitted through the earth from Lisbon, 



after being thu 



* Geol. Soc. Proceedings, No. 60, p. 36. 1838. 



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