56 STUDIES, SCIENTIFIC AND SOCIAL chap. 



But whatever doubts may still exist as to the exact 

 causes of these last-named phenomena do not apply to 

 those to which the present chapter is mainly devoted. So 

 many distinct but converging lines of evidence indicate the 

 existence of a molten substratum holding in solution, in 

 accordance with well-known physical laws, great quantities 

 of steam and other gases, and show that the crust covering 

 it is a very thin one — while the hypothesis of such a sub- 

 stratum and thin floating crust so well explains the curious 

 phenomena of great masses of strata thousands of feet 

 thick, yet from top to bottom bearing indications of having 

 been deposited in shallow water, and the no less singular 

 fact of a corresponding recent subsidence in all great river- 

 deltas, and also clears up so many difficulties in the modes 

 of volcanic action and the diversity of volcanic products — 

 that we can hardly doubt the correctness of the hypothesis. 

 And though at first sight the idea of our being separated 

 by a thickness of only eighteen miles of rock from a layer 

 of molten lava of unknown depth may appear somewhat 

 alarming, yet the very tenuity and fragility of the crust 

 may itself be a source both of safety and of utility. While 

 sufficiently thick to secure us from any injurious or even 

 perceptible effects of internal heat, except in volcanic or 

 earthquake areas, it yet gives us the possibility and even 

 the promise of an inexhaustible source of heat and power 

 at such a moderate distance that we may some day be able 

 to utilise it. On the other hand, the thin crust so readily 

 and constantly adjusts itself to all the alternations of strain 

 and pressure to which it may be exposed, that we are 

 thereby secured from the occurrence of vast cataclysms 

 capable of endangering the existence of any considerable 

 portion of our race. A solid earth might, possibly, not be 

 so safe and stable as is Our Molten Globe. 



