THE INTEEIOR OF THE EARTH. 233 



as growth proceeded. Special emphasis is laid on the selective 

 nature of vulcanism under this hypothesis. The intimate mixture 

 of planetesimals and planetesimal dust gave rise to a multitude of 

 minute contacts between particles of different chemical and physical 

 properties, and hence there arose wide differences in the solution 

 points. As the temperature in the growing planet rose, the more 

 soluble portions passed into the liquid state by stages long before 

 the remaining larger portion reached the temperature of solution. 

 In a stressed globe certain of whose stresses are more intense to- 

 ward the center than toward the surface, the solutions were forced 

 to work in the direction of least resistance — for them generally out- 

 ward — carrying out heat of liquefaction and leaving behind tiie less 

 soluble larger portion whose temperatures were inadequate for fur- 

 ther liquefaction until there was a renewed accession of heat. The 

 mechanism thus automatically tended to remove the most soluble con- 

 stituents by progressive stages, while it tended to preserve the solid 

 condition of the remaining mass. The hypothesis thus supplies a 

 working mechanism whose results fall into full accord with the states 

 of the interior implied by tidal investigations and by seismic data, 

 while the distribution of specific gravities naturally assignable under 

 it accords well with the best geodetic determination thus far made. 



The adaptation of such an earth to isostatic adjustment can 

 scarcely be more than hinted at here. The growth of the earth 

 should have given it a concentric structure, while its highly distribu- 

 tive vulcanism, together with some of its deformative processes, 

 should have given a vertical or radial structure, the two conjoining 

 to give a natural tendency to prismatic or pyramidal divisions con- 

 verging toward the center. The most powerful of all the deforma- 

 tive agencies — rotation — required for the adaptation of the earth to 

 its changes of rate such divisions of the earth body as would re- 

 spond most readily to depression in the polar and bulging in the 

 equatorial tracts reciprocally or their opposites. As urged else- 

 where, this accommodation seems best met by three pyramidal sec- 

 tors in each hemisphere, with apices at the center and bases at the 

 surface, the sectors in opposite hemispheres arranged alternately 

 with one another. Very simple motions within these sectors 

 would satisfy the larger demands of rotational distortion, while the 

 subsectors into which these major sectors would naturally divide, 

 as stresses required, would easily accommodate the nicer phases of 

 adjustment. This primitive segmentation to meet rotational de- 

 mands — which were most urgent during the stages of infall — fur- 

 nished a mechanism suitable for the easement also of a portion of the 

 deformational stresses that arose from other sources, among them 

 gravitative stresses arising from loading and unloading by erosion 



