for the Study of Megadiastrophism. 413 



results in a more nearly perfect isostatic balance. Dias- 

 tropliism is then the corrective. This is the view so ably 

 developed by Barrell in his monumental treatise on ' ' The 

 Strength of the Earth's Crust." 45 Heterogeneities of 

 load whether due to erosion, deposition, or to the intro- 

 duction of intrusive or extrusive masses control, within 

 the limits imposed by crustal strength and distribution, 

 the degree of adjustment attained. These heterogenei- 

 ties are for the most part visible and determinate. 

 Beneath this heterogeneous layer, according to the evi- 

 dence both of the igneous rocks and transmitted seismic 

 vibrations, there lies homogeneous material which is 

 capable of yielding under the larger differential stresses 

 to which it is subjected. Broad scale heterogeneities of 

 the surface shell must result in similarly broad scale and 

 generally permanent major reliefs. This view is based 

 upon what we can see. The opposing view — that of 

 Chamberlin — must be built upon an assumed asymmetric 

 earth core upon which was laid down, over a period 

 covering several billion years and through the whims of 

 the atmosphere, a selective rain of planetesimal dust. 

 This constitutes the foundation for the study of ^megadi- 

 astrophism." Is that foundation secure? 



But the conception of an isostatic heterogeneous shell 

 resting upon a homogeneous yield zone does not, of 

 course, permit the application of deeply pointing wedge 

 deformation to areas of continental dimensions. 



Massachusetts Institute of Technology, 

 Cambridge, Mass. 



45 Joseph Barrell: The Strength of the Earth's Crust: Jour. Geology, 

 vols. 22, 23, 1914-1915. 



