BOOK II. Lxxxi. 192-LXXX11. 194 



occur except v/hen the sea is calm and the sky so 

 Btill that birds are unable to soar because all the 

 breath that carries them has been withdrawTi ; and 

 never except after wind, doubtless because then the 

 blast has been shut up in the veins and hidden hol- 

 lows of the sky. And a trembhng in the earth is 

 not ditferent from a thunderclap in a cloud, and a 

 fissure is no different from when an imprisoned 

 current of air by strugghng and striving to go forth 

 to freedom causes a flash of hghtning to burst out. 



LXXXII. Consequently earthquakes occur in a thnr 

 variety of ways, and cause remarkablc consequences, f,',^^"""'^' 

 in some places overtlirow.ing walls, in others drawing (omeiwnc. 

 them dowTi into a gaping cleft, in others thrusting up 

 masses of rock, in others sending out rivers and 

 sometimes even fires or hot springs, in others divert- 

 ing the course of rivers. They are however preceded 

 or accompanied by a terrible sound, that sometimes 

 resembles a rumble, sometimes the lowing of cattle 

 or the shouts of human beings or the clash of weapons 

 struck together, according to the nature of the 

 material that receives the shock and the shape of the 

 caverns or burrows througli which it passes, proceed- 

 ing with smaller vohmie in a narrow channel but with 

 a harsh noise in channels that bend, echoing in 

 hard channels, bubbhng in damp ones, forming waves 

 in stagnant ones, raging against sohd ones. Ac- 

 cordingly even without any movement occurring a 

 sound is sometimes emitted. And sometimes the 

 earth is not shaken in a simple manner but trembles 

 and vibrates. Also the gap sometimes remains 

 open, showing the objects that it has sucked in, 

 while sometimes it hides them by closing its mouth 

 and drawing soil over it again in such a way as to 



325 



