ON ITS EXTERIOR. EARTHQUAKES. 169 



regions is furnished by geological conjectures respecting 

 the non-connection of volcanically upheaved masses of 

 rock. I have brought together the following brief no- 

 tices of the different views which have been taken of 

 the possible nature of the first impulse in earthquake 

 movements : - 



In one of these views the interior of the earth is 

 regarded as being in a state of igneous fluidity; the 

 result of the process of formation of planets from a 

 gaseous state, whereby, in the transition from fluid to 

 solid, great disengagement of heat took place ; the 

 external strata, by radiation of their heat into space, 

 having been the first to cool down and solidify. The 

 unequal ascent of elastic vapours (formed at the limits 

 between the fluid and solid, either from the molten 

 mass of the earth only, or by the penetration of sea- 

 water), the sudden opening of fissures thereby occa- 

 sioned, and the sudden approach of these vapours, 

 formed at great depths, and having therefore great 

 heat and tension, to the higher rocky strata nearer 

 to the earth's surface, are supposed to occasion agi- 

 tation, and to give the first impulse to the earthquake- 

 wave. An auxiliary influence, due to a non-telluric 

 cause, is supposed to exist in the attraction of the 

 moon and sun ( 234 ) acting on the fluid molten surface 

 of the earth's nucleus, whereby there must arise in- 

 creased pressure, either immediately, against a solid 

 superincumbent rocky vault, or mediately, where in 

 subterranean basins the solid is separated from the 

 liquid molten mass by elastic vapours. 



In another view the nucleus of our planet is regarded 



