THE EARTH. 95 



every appearance that attends these tremendous 

 irregularities of nature. To conceive this dis- 

 tinctly, let us suppose, at some vast distance 

 under the earth, large quantities of inflammable 

 matter, pyrites, bitumens, and marcasites, dis- 

 posed, and only waiting for the aspersion of 

 water, or the humidity of the air, to put their 

 fires in motion ; at last, this dreadful mixture 

 arrives ; waters find their way into those depths, 

 through the perpendicular fissures ; or air insi- 

 nuates itself through the same minute apertures : 

 instantly new appearances ensue : those sub- 

 stances, which for ages before lay dormant, now 

 conceive new apparent qualities ; they grow hot, 

 produce new air, and only want room for expan- 

 sion. However, the narrow apertures by which 

 the air or water had at first admission, are now 

 closed up ; yet, as new air is continually gene- 

 rated, and as the heat every moment gives this 

 air new elasticity, it at length bursts, and dilates 

 all round ; and, in its struggles to get free, 

 throws all above it into similar convulsions. 

 Thus an earthquake is produced, more or less 

 extensive, according to the depth or the great- 

 ness of the cause. 



But before we proceed with the causes, let us 

 take a short view of the appearances which have 

 attended the most remarkable earthquakes. By 

 these we shall see how far the theorist corresponds 

 with the historian. The greatest we find in an- 

 tiquity, is that mentioned by Pliny,* in which 



IMiii. lib. ii. cap. 8G. 

 18 



