ADVANCED SUMMARY 249 



form density distribution in a vertical column, and to that of hydrostatic 

 pressures below the zone of compensation. The existence of a zone of 

 compensation is, nevertheless, regarded as established by his researches. 

 It is defined as a zone of solid rock of great strength and of variable 

 thickness, which passes, at its lower limit, into the asthenosphere of 

 Barrell. The anomalies of gravity which have been demonstrated by 

 the researches of Hayford and Bowie are considered to be those superficial 

 effects of unequal attractions exerted by bodies of different densities 

 which lie near enough to produce notable anomalies. The anomalies are 

 not regarded as unique, however, nor confined to the isostatic shell. Fol- 

 lowing Gilbert, nucleal heterogeneity is regarded as highly probable. The 

 fact that its effects are not evident is attributed to the law of averages 

 among large numbers of small differences, to the masking of the deep- 

 seated anomalies by the asthenosphere, and to their distance from the 

 observer on the surface. 



The development of a certain structure in the lithosphere is attributed 

 to recrystallization of rocks under non-uniform stress, the result being 

 a foliation which is oriented by the stress. Although erosion and depo- 

 sition are not regarded as capable of producing mass movement or 

 "undertow," they are considered competent to set up a stress within the 

 elastic limit of the lithosphere which does determine tlie direction taken 

 by foliation, provided a rise of temperature or other external force causes 

 recrystallization. The orientation of the elastic stress, and conseqnently 

 of the foliation, is approximately vertical in the unloaded mass, but is 

 horizontal in the loaded mass and curves from beneath the latter upward 

 into the former. Thus, under any sinking, overloaded area there de- 

 velops a curved foliation which gives rise to a disk-like structure. Disks 

 obviously correspond with heavier bodies, whereas the lighter bodies, in 

 which foliation is predominantly vertical, may be called interdisks. 



An analysis of continental structure and of oceanic basins leads to the 

 conclusion that the continental platforms and the underbodies of the 

 ocean consist of heavier and lighter masses corresponding to disks and 

 interdisks. The inference regarding curved foliation, which throughout 

 the previous argument is attributed to elastic stresses set up by erosion 

 and deposition, is extended to broad oceanic depressions by consideration 

 of the stresses which would be produced in the underbody, if the deeps 

 resulted from subsidence of heavy masses. 



Throughout the argument the structural relation between foliation and 

 the course taken by rising igneous masses is used as a means of recogniz- 

 ing the original foliation of the rocks. The argument suggests that the 

 Igneous material which is erupted in the margins of the continents. 



