EFFECTS OF EAETHQUAKES ON LAND. 153 



From this we see that liquids may rise far beyond the 

 level due to hydrostatic pressure.^ 



Volger has attributed the origin of lights or flames 

 appearing above fissures to the friction which must take 

 place between various rocky materials at the time when 

 the fissures are opened. As confirmatory of this he refers 

 to instances where similar phenomena have been observed 

 at the time of landslips. At the time of these landslips 

 the heat developed by friction has been sufficiently in- 

 tense to convert water into steam, the tension of which 

 threw mud and earth into the air like the explosion of a 

 mine.^ 



The gas eruptions which occasionally take place with 

 earthquakes are probably due to the opening of fissures 

 communicating with reservoirs or strata charged with 

 products of natural distillation, or chemical action, which 

 previously had accumulated beneath impervious strata. 

 Of the existence of such gases we have abundant evidence. 

 In coal mines we have fire-damp which escapes in increased 

 quantities with a lowering of the barometrical pressure. 

 In volcanic regions we have many examples of natural 

 springs of carbon dioxide. 



These various gases sometimes escape in quantity, or 

 erupt without the occurrence of earthquakes. Rossi men- 

 tions an instance where a few years ago quantities of fish 

 were killed by the eruption of gas in the Tiber, near Eome. 

 Another instance is one which occurred at Follonica on 

 April 6, 1874. On the morning of that day many of the 

 streets and roads were covered with the dead bodies of 

 rats and mice. It seemed as if it had rained rats. From 

 the facts that the bodies of the creatures seemed healthy, 



Oldham and Mallet, ' Cachar Earthquake,' Trans. Geolog. Soc. Ap. 

 1872. 



^ 0. Volger, Uhters ub. d. Phdn. d. Erdh, vol. iii. p. 414. 



