202 O. C. JONES, GEORGE D. HUBBARD Vol. XXII, No. 7 



the actual shortening lies between 70 and 140 km., thoroughly 

 beyond the power of increased temperature to create. 



Intense normal faulting follows intense folding almost 

 without exception. 



Extensive faulting is usually apparently confined to regions 

 of thick sedimentation. It is difficult, however, to detect faults 

 in igneous rocks, also in some metamorphics. This may help 

 to explain the apparent distribution of faults. 



THE CENTROSPHERE. 



The term " centrosphere " may be used to include that por- 

 tion of the earth throughout which rocks are adjustable to 

 stress through flowage, and in which cavities and fractures do 

 not exist. It would thus be within the so-called "crust" 

 or zone of fracture. The seismographic evidence shows two 

 very important things in regard to this interior; first that it 

 is solid, because it everywhere transmits transverse waves, 

 which cannot pass through a liquid — this evidence is conclusive; 

 secondly, that it is increasingly dense toward the center, 

 attaining a specific gravity of 6 at .4 radius distance from the 

 center — evidence calculated from the rate of wave transmission 

 through the interior. At this rate of progression a density of 

 8.22 would be attained at the center, assuming the surface 

 density to be 2.67. It is unlikely that this progression holds 

 beyond this depth, because the mean density of 5.6 requires a 

 central density of 11. Down to a depth of .6 radius the 

 increased density is thought to be only that due to increased 

 pressure; below this depth the earthquake researches of Oldham^^ 

 may throw some light on the problem. He found that at a 

 distance of approximately of 130 degrees from the point of 

 origin, distortional waves were suddenly broken off to be 

 continued beyond this distance approximately 11 minutes 

 later. Just what inferences should be drawn from this, it is 

 not possible to say, except that it is altogether likely that there 

 exists a central core of about .4 radius extent from the center, 

 required by other facts to have a density very high, probably 

 between 8 and 11, and if dense to have a refraction of at 

 least 2. 



Some conclusions may be drawn as to rock flowage through 

 the centrosphere. Granite has a crushing strength of 1,425 



