Lesson xxxv.] EARTHQUAKES. 261 



up from the deck. Immediately after this, the 

 ship sunk in the water as low as the main chains. 

 The lead shewed a great d^pth of water, and the 

 line was tinned of a yellow colour, and smelt of 

 sulphur. The sh >ck las't-d about ten minutes, but 

 they felt^maller ones for the space of 24 hours. 



Such were the phaenomena of this very remark- 

 able and destructive earthquake, which extended 

 over a tract of at least four millions of square miles. 



There have been various hypotheses entertained 

 "with regard to the production of Earthquakes ; nor 

 does it appear an easy task to account for them 

 with great precision. Those which are only felt at 

 small distances are probably occasioned by the 

 action of subterraneous fires, and the explosion 

 of volcanoes. But there have been Earthquakes 

 which are felt at great distances, and have shaken 

 an extensive tract of country : this kind of Earth- 

 quakes is by some persons accounted for in the 

 following manner. 



To understand properly what .may be the cause 

 of these ; hoeuomcua, it must be remembered, that 

 all inflammable matters capable of explosion pro- 

 duce, like gunpowder, by inflammation, a great 

 quantity of air j that this air produced by fire is in 

 a state of very great rarefaction j and that, by a 

 state of compression in which 'it is found in the 

 bowels of the earth, it must produce very violent 

 "fetTects. It is then conjectured, that at a consider- 

 able depth, as at about one or two hundred fa- 

 thoms, pyrites and other sulphureous matters are 

 to be met with ; and that by the fermentation pro- 

 duced 



