Interior of the Globe, 



37 



C The centre of the globe. 



L The shell or crust of solid matter, whose depth is as- 

 Bumed to be 1000 miles, or one-fourth of the radius 8 0. 



8 8 The surface of the globe, or outer boundary of the crust. 



1 1 The inner surface or boundary of the solid crust. 



N The interior, which may be filled with matter, either fluid 

 or solid. 



r r Eeservoirs of fluid matter, at a moderate depth under 

 the surface, which produce movements of elevation and give 

 birth to volcanoes. 



Mr Hopkins thinks the origin of these subterranean lakes 

 or insulated masses of fused matter, may be ascribed to two 

 causes ; first, the greater fusibility of the matter composing 

 them ; and, secondly, a relaxation of the pressure, which coun- 

 teracts fluidity. We know that there is a great difference in 

 the fusibility of the rocks forming the outer parts of the globe ; 

 and we have no reason to doubt that there may be a similar 

 diff'erence in the matter existing at a greater depth. We 

 know, too, that when certain substances which act as fluxes 

 happen to be present, fusion is facilitated. The greater fusi- 

 bility of some parts being admitted, Mr Hopkins shews how 

 it might be sustained or increased by upheavals ; and his 

 hypothesis has the further merit of explaining very happily a 

 phenomenon attending elevatory movements which has hitherto 

 puzzled geologists. 



Jl>.5 



C ^ ^ ^ ^ 



^ I 



Let A B, fig. 3, represent a transverse section of a portion 



