ipis.] EARTH FROM THE VIEWPOINT OF GEOLOGY. 289 



main mass. The hypothesis thus supphes 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 pos- 

 tulated distribution of specific gravities accords fairly well with 

 geodetic determinations, as they now stand. 



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. As urged elsewhere, this accommo- 

 dation seems best met by three pyramidal sectors 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 of these sectors on their apices at the earth's center 

 would satisfy the larger demands of rotational distortion, while the 

 sub-sectors 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 

 and sedimentation. A gravitational adjustment by the wedging up 

 and down and laterally of such sectors is thus offered tentatively as 

 a working competitor to theories of adjustment by fluidal or quasi- 

 fluidal undertow. The necessary brevity of this statement leaves 

 this new hypothesis little more than a crude suggestion that gravi- 

 tative adjustment (=isostasy) may perhaps take place as fully as 

 the case requires in a highly rigid elastic earth without resort to 

 flowage or even quasi-flowage. 



The University of Chicago. 



