as a Cause of Earthquakes. 87 



April 23. 1839, water issued up to a considerable height 

 through the openings of the earth. It is not requisite to enu- 

 merate more instances of the effusion of water which gene- 

 rally takes place at the time of earthquakes which are not 

 connected with volcanic action, as they may be found in the 

 works of Lyell and other geologists. The above are sufficient 

 to shew that hydrostatical pressure, producing sudden frac- 

 tures and eruptions of the under strata, if not the sole cause, 

 is, in general, acting forcibly at the time of their shocks. 



It is, perhaps, difficult to assign any other cause than that 

 of hydrostatical pressure to the circumstances of earthquakes 

 frequently occurring longitudinally in parallel directions to 

 the chains of mountains in the neighbourhood. This was the 

 case in the plains of the Mississippi in 1811, where the chains 

 were all parallel and in the same direction from S W. to NE. 

 as the Alleghany range. Professor Bischof, in his memoirs upon 

 volcanos and earthquakes (published in this Journal), states this 

 to have occurred in the Pyrenees, on December 28. 1779, July 

 10. 1784, July 8. 1791, May 22. 1814, &c. ; also earthquakes in 

 South America seem to follow the direction of the mountains. 

 Thus, that at Caraccas in 1812 followed the direction of the 

 littoral Cordilleras from E.N.E. to W.S.W. That of Cumana 

 in 1797 presented an instance of the same fact. The predo- 

 minant direction of the frequent earthquakes on the coast of 

 Chili and Peru is also that of the large chain of the Andes, 

 which is parallel to the coast. All the older reports likewise 

 state that in these countries their direction is from S. to N., 

 or vice versa ; and Mrs Graham remarked that she felt, during 

 the violent earthquake in Chili in 1822, as if the whole ground 

 from north to south were suddenly raised and then sunk again. 



If it be supposed that there are hollows under the moun- 

 tains in consequence of their original elevations, and that they 

 are filled with water, the earthquake might arise from the ac- 

 tion of water under the plains, which was rendered sufficiently 

 powerful from an additional quantity, owing to rain or the 

 melting of snow, having added to the heights of the commu- 

 nicating vertical columns. That cavities do often exist under 

 great elevations is evident from the frequent instances of 

 their falling in which are given in various geological works, 



