154 EARTHQUAKES. 



that the destruction had happened suddenly, and not 

 come on gradually like an epidemic, it was supposed that 

 they had been destroyed by an emanation of carbon di- 

 oxide. The fact that many of them lay in long lines 

 suggested the idea that they had been endeavouring to 

 escape at the time of the eruption.^ If we can suppose 

 sudden developments of gas like this to have occasionally 

 accompanied earthquakes, we may sometimes have the 

 means of accounticg for the sickness which has been felt. 



Disturbances in lakes, — It has often been observed 

 that, at the time of large earthquakes, lakes have been 

 thrown into violent agitation, and their waters have been 

 raised or lowered. At the time of the great Lisbon earth- 

 quake, not only were the waters of European lakes thrown 

 into a state of oscillation, but similar effects were pro- 

 duced in the great lakes of North America. In some 

 instances, as in the case of small ponds, these movements 

 may be produced by the horizontal backward and forward 

 motion of the ground. At other times they are probably 

 due to an actual tipping of a portion of their basins. 

 Movements like these latter will be again referred to in 

 the chapter on Earth Pulsations. On January 27, 1856, 

 there was a shock of earthquake at Bailyborough, Ireland, 

 which occasioned an adjacent lough to overflow its banks 

 and rush into the town with great impetuosity. In return- 

 ing it swept away two men, leaving behind a great quantity 

 of pike and eels of a prodigious growth.^ 



Disturbances in rivers. — Just as lakes have been 

 disturbed, so also have there been sudden disturbances in 

 rivers. Sometimes these have overflowed their banks, 

 whilst at other times they have been suddenly dried up. 



In certain cases the reason that a portion of a river should 



* 



* Meteorologia I/adogena., vol. i. p. 166. 



* Gent. Mag. vol. xxvi. p. 91. 



