220 EARTHQUAKES. 



or, what is the same thing, by the ratio of the altitudes 

 of the volcanoes of the Andes to that of Vesuvius.' 



Now, as the depth of the Neapolitan shock may be 

 taken at 34,930 feet, the greatest probable depth of origin 

 of any earthquake impulse occurring in our planet is 

 limited to 5*333 x 4,930 feet, or 30*64 geographical miles. 



Ingenious as this argument is, we can hardly admit it 

 without certain qualifications. 



First, we are called upon to admit the identity of the 

 originating cause of the volcano and the earthquake — as 

 to what may be the originating cause of earthquakes we 

 have yet to refer, but certainly in the case of particular 

 earthquakes, as, for instance, those which occur in countries 

 like Scotland, Scandinavia, and portions of Siberia, the 

 direct connection between these phenomena are not at first 

 sight very apparent. 



Secondly, even if we admit the identity of the origin 

 of these phenomena, it is not difficult to imagine that 

 the fluid pressure brought to bear upon certain portions 

 of the crnst of the earth may possibly in many instances 

 be infinitely greater than that indicated by the height 

 of the column of liquid lava in the throat of a volcano, 

 the true height of which we are unable to obtain. 

 P'urther, in certain instances such a column only appears 

 to be a measure of the pressure upon the crust of the 

 earth in the immediate vicinity of the cone. 



Thus, in the Sandwich Islands, we have lava standing 

 in the throat of the volcano of Mouna Loa 10,000 feet 

 higher than it stands in the crater Kilauea, only twenty 

 miles distant. That these columns should be measures 

 of the same pressure, originating in a general subterranean 

 liquid layer with which they are connected, is a supposition 

 difficult to satisfactorily substantiate. 



Another measure of the impulsive efforts which sub- 



