THE STRENGTH OF THE EARTH'S CRUST 673 



of the crust against another, presumably offset by tension in some 

 other region. Button's argument is that the crust beneath the 

 plateau is unloaded by erosion, that the crust beneath the basin is 

 loaded by sedimentation. An isostatic movement, rejuvenating 

 the relief, must, by causing the overloaded basin to settle, produce 

 a squeezing-out of matter beneath the sinking area, and a crowding- 

 in of matter beneath the rising area. The surficial movement of 

 sediment is from the high area toward the low. The deep-seated 

 movement is from the low toward the high. Thus the cycle 

 becomes completed and the mass of matter above the level of com- 

 plete compensation remains the same in each column. The seaward 

 movement of the sediment, as a frictional resistance against the 

 river bottoms, produces only an insignificant drag, but the return 

 subterranean movements by viscous or solid flowage must produce 

 a pronounced drag upon the crust in the direction of the rising 

 region. Button's reasoning is clear, but the effectiveness of the 

 action rests upon several assumptions. First, it omits the influence 

 of the surface relief and the degree to which that tends to a lateral 

 spreading movement from the high toward the low regions. Sec- 

 ondly, it postulates a low rigidity to the crust, as he in fact notes. 

 Thirdly, it involves the conception of a strong undertow fairly 

 near the surface in order that the crust above may be too weak to 

 resist the viscous drag. As there were little quantitative data 

 available at the time when Button formulated this corollary of his 

 theory of isostasy he could not have tested the validity of these 

 assumptions, but raised the problem for those who should come 

 after him. 



This theory of folding took a somewhat different form in the 

 mind of Willis, as expressed in the concluding chapter of his 

 Research in China} This work in many ways is of the very first 

 importance and gives a comprehensive view of the geological history' 

 of the whole continent of Asia. As to the nature of the movements, 

 he finds that the continent of Asia may be resolved into positive 

 and negative elements, the former areas tending to stand high, the 

 latter tending to stand low. These tendencies are latent during 

 comparatively long periods of quiet and resultant peneplanation, 



' Vol. II (1907), Carnegie Institution of Washington. 



