109 



A short notice of Earthquakes. 



[January 



India, it extends from the Phillippine Islands as far south as 

 Java, and runs as far to the north as Barren Island, in the Bay of 

 Bengal. In all of this tract there are ample evidences of the inti- 

 mate relation of earthquakes and volcanoes. This relation and af- 

 finity being allowed, it only remains for me to make a few general 

 remarks. From chemical researches, it is well known that various 

 changes are going on in the surface of the earth, there being a con- 

 stant state of waste and repair, chemical composition and decom- 

 position, it cannot therefore be supposed that the interior of the 

 globe is one inert and dormant mass. It is well known that at the 

 periods preceding the eruption of volcanoes, earthquakes were fre- 

 quent, and that various vapours, gases, and other sul)stances, the 

 result of chemical decomposition escaped suddenly at those periods, 

 and must have been detained below, under a high state of compres- 

 sion, and that these eruptions were attended by a period of subse- 

 quent rest. May we not therefore reason justly from these visible ef- 

 fects that the same changes are going on at greater depths and in 

 larger cavities in the interior of the earth by which explosive com- 

 pounds, whether gaseous, or solid, may be produced, vapours con- 

 densed, and changes take place similar to those of volcanic action, 

 although at so great a depth, as to be beyond the reach of observati- 

 on, which however may be capable of exerting an excessive mecha- 

 nical power, equal to that required to produce extensive earthquakes. 

 There is a valuable remark in Ure's work, that primitive formations 

 which are oxydized at the surface of the earth exist at a moderate 

 depth devoid of oxygen in the state of simple combustibles, he states 

 " that the crust of the earth consists mainly of six substances, Silica, 

 Alumina, Iron, Lime, Magnesia, and Potash, which when reduced by 

 the chemist to a state of simplicity, become the combustible ele- 

 ments Silicon, Aluminum, Calceum, Magnesium, Polassium, Iron, 

 a mixture of which at common terpperatures on coming into contact 

 with water or moist air, would cause fire and explosion — and if the 

 quantities were great, earthquakes and volcanic eruptions would 

 ensue." 



Lyall, tov/ards the conclusion of his first volume reasons ^'that 

 the renovating and destroying causes in the earth are constantly at 

 work, the repair of land being as constant as its decay, the deepen- 

 ing of seas keeping pace with the formation of shoals — he says that 

 if in the course of a century, the Ganges and other great rivers have 

 carried down to the sea, a mass of matter equal to many lofty 

 mountains, we also find that a District in Chili one hundred 



