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succession of short sudden shocks. The effects of the shocks 

 were different in different parts of the island ; there did not 

 seem to be any regular track pursued by the earthquake ; in 

 places within a few miles of each other, in one it was not felt at 

 all, while in the other it was quite severe. At Mariveles, just 

 across the Bay from Manilla, the earth opened, with an eruption 

 of black sand, which covered the country for a considerable 

 extent ; how large the opening was at the time is not known, 

 but it is now seven hundred yards long and one yard wide. The 

 volcanoes at Albay and Taal, which have not been in operation 

 for many years, have been since discharging lava, stones, &c. 

 with considerable activity." 



Prof. Rogers referred to the circumstance that the un- 

 dulatory movement of an earthquake is felt much more 

 sensibly at a point above the earth's surface than directly 

 upon it. An instance illustrating this had come within his 

 own knowledge. The earthquake which destroyed the 

 principal city of Guadaloupe was felt in the city of New 

 York, but only in the fourth story of a printing office. The 

 sound generally precedes the shock, as has been observed 

 in this country. In North America, the undulation is 

 always parallel to the physical features of the continent, 

 making it reasonable to believe that through a long series 

 of epochs the motion has been in one rather than various 

 directions, as supposed by Elie de Beaumont. There are 

 two movements in earthquakes ; an undulating and a mole- 

 cular movement. The latter, Prof. Rogers thought was 

 the movement wdiich attracted most observation, giving 

 rise as it does to sudden and abrupt changes of relation on 

 the surface of the earth at places where the formation of 

 the strata admits of more or less freedom of movement, 

 causing the sudden shocks which are so destructive. Prof. 

 Rogers gave an account of some of the opinions of geolo- 

 gists as to the thickness of the earth's crust. He gave it as 

 his own opinion, that in most places it is not more than ten 

 miles thick. 



