THE STRENGTH OF THE EARTH'S CRUST 501 



all known substances, and therefore the hquid magma passes into 

 a gaseous magma extending to the center of the earth. The author 

 then notes that the chemical elements of highest atomic weight 

 are not detected in the sun, but states that without doubt they 

 occur, and concludes from this that they must be concentrated 

 by virtue of gravity toward the sun's center/ The high density 

 of the earth's interior is accordingly to be explained by the presence 

 of substances heavier than surface rocks. For many reasons, as 

 the dominance of iron in nature, as shown by meteorites., by the 

 spectrum of the sun, and by the magnetism of the earth, it is to be 

 concluded that this substance which he thinks necessary to account 

 for the high density of the earth's interior is metalHc iron. The 

 earth consists consequently of the following portions measured 

 from the center on the radius. Eighty per cent of the radius is 

 gaseous iron, 15 per cent is gaseous rock magma, about 4 per cent 

 is fluid rock magma, and somewhat less than one per cent is solid 

 crust." 



To reconcile these conclusions with the incontrovertible evi- 

 dence of rigidity, Arrhenius takes up another line of rectilinear 

 extrapolation and carries it to an equally extreme degree. Fluids 

 in general show a somewhat readier compressibility than sohds. 

 At high pressures then it is argued that liquids will customarily 

 occupy less volume than soUds and the pressure will tend to lower, 

 not raise, the melting-point. Consequently, the rigidity cannot 

 be accounted for by the maintenance of solidity through pressure. 

 The author then points out that under enormous pressures all sub- 

 stances, even gases, must become highly incompressible; and that 

 at high temperatures, where the volume is maintained the same, the 

 viscosity of gases or fluids increases with increase in temperature. 

 From this it is argued that in the central parts of the earth gaseous 

 iron is more incompressible and viscous than solid steel. It is 

 by enormous pressure consequently in spite of a gaseous nature 

 that the interior of the earth exhibits its great rigidity. 



Vulcanism according to Arrhenius is connected with the free 

 seepage of ocean water downward through the crust which, he 

 holds, constitutes a semipermeable membrane. By the absorp- 



" Op. Cit., p. 402. 2 Qp^ (;ll^^ p_ ^Q^. 



