6o 



THE FLOOR OF THE OCEAN 



aluminum, and the underlying simatic sub-layers, basaltic and 

 peridotitic. 



This crust-substratum hypothesis has bearing on almost 

 every phase of physical geology. Its broader implications have 

 been analyzed in several books. 2 On the present occasion only 

 two aspects of the subject will be considered; each deserves 

 attention because of the recent discovery of relevant, vital facts. 

 The marine volcanic mountains are localized masses of erupted 

 lava resting on the general sea floor. Can the crust-substratum 

 hypothesis tell us how lava can be lifted high above sealevel? 

 Are the great loads of lava being stably supported? If they 

 are, their support must come from the crust alone, for the 

 substratum is assumed to have negligible strength. 



It is to the advantage of the hypothesis that it almost auto- 

 matically answers the first question. If the substratum is glassy 

 because hot, it is eruptible. If some force opens a fissure ex- 

 tending from bottom to top of the crust, the essentially liquid 

 glass, under an initial pressure of the order of 200 tons to the 

 square inch, is shot upward into the fissure. On the left side 

 of each section in Figure 31 (drawn on the assumption that 



Sealevel 



CRATER LAVA- LAKE 

 AT 3000-4000 M. 

 ABOVE SEALEVEL 



I atm. 

 '//for*—- 



10,000 



R 



atm 



u 



T 



SUBSTRATUM mmLmm 



SUBSTRATUM 

 FIGURE 31. SECTION ILLUSTRATING THE RELATION OF SUBSTRATUM 

 TO VOLCANISM. 



