248 OUR HERITAGE THE SEA 



imagine. I am fully persuaded in my own mind that 

 the bed of the sea is the breeding place of earth- 

 quakes, and that the reason of their being so much 

 more prevalent in some parts of the world than in 

 others must be looked for in the fact that the gigantic 

 concussions consequent upon these submarine ex- 

 plosions take certain given directions laid down for 

 them by the geological configuration of the earth ; for 

 it is well known that the harder the substance the 

 greater the effect of an explosion upon it, and the 

 farther reaching its effects. But in any case so great 

 is the concussion that its effects may be observed all 

 over the world, although in many places quite delicate 

 instruments must be used, known as seismometers, in 

 order to note and record the tremors of the earth. 



Another reason why earthquakes are more prevalent 

 in some places than others is, I suppose, that in such 

 places there are usually vent-holes for the subterranean 

 fires which, presumably from the lie of the strata 

 beneath the volcano, come much nearer to the surface 

 in these places than in others, and consequently the 

 pent-up volume of steam, taking the line of least 

 resistance, rushes towards these outlets, shattering the 

 intervening rocks in its way. I consider it to be a 

 striking confirmation of this theory, that all terrestrial 

 active volcanoes are near the sea ; and the extinct ones 

 in places remote from the margin of the ocean appear 

 as if by the intervention of some cosmic upheaval they 

 had been thus isolated from the element which had 

 been the proximate cause of their elevation. And 

 therefore the same remarks which I have ventured to 

 make as to the cause of earthquakes will apply with 

 equal force to volcanoes, which, I take it, are in most 



