INTERNAL FLUIDITY OF THE EARTH. 



It is no rhetorical exaggeration that the globe we live on is a 

 stupendous, but very thin spherical shell, charged with liquid fire ; 

 and if such be the case it may naturally be asked how it happens, 

 that so thin a crust supported on a fluid so mobile can maintain that 



Fig. i. 



general state of stability which characterises it so strongly, that it 

 is referred to in times ancient and modern as the type of all that 

 is most solid and most durable. An answer to this reasonable 

 question will be collected from all we shall have to explain in the 

 present Tract.* 



14. The investigation of the structure and condition of this 

 solid crust of the terrestrial spheroid, extending from the fluid 



* According to Mr. Hopkins, the thickness of the crust is subject to 

 much local variation, being very unequal on its inner surface. He con- 

 siders that it is probably cavernous, and that masses of fluid mineral 

 matter may be distributed through its cavities. According to him the 

 thickness in some parts may be as great as 800 or 1000 miles. See 

 Memoirs on the State of the Interior of the Earth, in the Philosophical 

 Transactions from 1839 to 1842. 



37 



