46 THE FLOOR OF THE OCEAN 



sidered a good working hypothesis — that the deep layer is so 

 hot as to be actually vitreous. This hypothesis seems to be the 

 only one that is well grounded on geological and geophysical 

 observations. 



5. A red-hot to white-hot, glassy layer would react to earth- 

 quake waves as if it were solid, and yet to stresses of much 

 longer duration it would react like a viscous liquid. If we do 

 assume the existence of a glassy layer just beneath the crust, 

 we have gone far toward answering an early principal ques- 



CRYSTALLIZED SIMA 



SIAL 



SIALv^S ~Ji 



FIGURE 22. STEREOGRAM TO ILLUSTRATE THE EARTH-SHELLS AS DEDUCED 



FROM DATA SUPPLIED BY SOME SEISMOLOGISTS AND BY OBSERVATIONS IN 



GENERAL GEOLOGY. 



