198 



CHAPTER XXXII 



CAUSES OF EAETHQUxVKES AITD VOLCA]S"OS. 



INTiaiATK CONNECTIOK BETWEEN THE CAUSES OF VOLCANOS AND EARTH- 

 QUAKES — SUPPOSED ORIGINAL STATE OF FUSION OF THE PLANET — ITS SIMUL- 

 TANEOUS AND UNIVERSAL FLUIDITY NOT PROVED BY ITS SPHEROIDAL FIGURE 



ATTEMPT TO CALCULATE THE THICKNESS OF THE SOLID CRUST OF THE EARTH 

 BY PRECESSIONAL MOTION HEAT OF EARTh's CRUST INCREASING WITH THK 



DEPTH, BUT NOT EQUALLY 



NO INTERNAL TIDES OF SUPPOSED CENTRAL 



FLUID PERCEPTIBLE SUPPOSED CHANGE OF AXIS OF EARTH S CRUST —PARTIAL 



FLUIDITY OF THE EARTh's CRUST MOST CONSISTENT WITH VOLCANIC PHE- 

 NOMENA OF THE PAST AND PRESENT ABANDONMENT OF THE DATA BY WHICH 



THE EARLIER GEOLOGISTS SUPPORTED THEIR THEORY OF THE PRISTINE 



FLUIDITY OF THE EARTh's CRUST DOCTRINE OF A CONTINUAL DIMINUTION 



OF TERRESTRIAL ANT) SOLAR HEAT CONSIDERED. 



It will liardly be questioned, after the description before 

 given of tbe phenomena of earthquakes and volcanos, that 

 both of these agents have, to a certain extent, a common 

 origin ; and I may now, therefore, proceed to enquire into 

 their probable causes. But, first, it may be well to re- 

 capitulate some of those points of relation and analogy which 

 lead naturally to the conclusion that they spring from a 

 common source. 



The regions convulsed by violent earthquakes include 



the site of all the active volcanos. Eartli- 



m 



within thi 



quakes, sometimes local, sometimes extending over vast 

 areas, "often precede volcanic eruptions. The subterranean 

 movement and the eruption return agrain and again, at ir- 



regular intervals of time, and with unequal degrees of force, 

 to the same spots. The action of either may continue for a 

 few hours, or for several consecutive years. Paroxysmal 

 convulsions are usually followed, in both cases, by long 

 periods of tranquillity. Thermal and mineral springs are 

 a,bundant in countries of earthquakes and active volcanos. 

 liastly, springs situated in districts considerably distant 



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