Febbtjabt 10, 1911] 



SCIENCE 



205 



The effect of increased pressure tends to 

 produce chemical changes accompanied by 

 decrease of volume and so to produce a 

 sinking of the surface. The blanket of de- 

 posited material tends to raise the tem- 

 perature in each part of the material 

 covered, to increase the volume of this 

 material, and thereby to raise the surface. 

 The temperature effect may serve in time 



comparatively neutral region between the 

 two in which neither erosion nor deposi- 

 tion is much in excess of the other, see Fig. 

 2. Hence the undertow by increasing the 

 temperature and causing a change of den- 

 sity may be directly effective in changing 

 the elevation of the neutral region be- 

 tween two regions of deposition and 

 erosion. 



REGION OF EROSJON 



UtUTRAL REGION 



REGION or DEPOSITION 



UNDERTOW 



DEPTH or COMPENSATION 



to arrest the subsidence caused by in- 

 creased pressure or even to raise the sur- 

 face and change the region of deposition 

 into one of erosion. 



The changes of temperature just de- 

 scribed are due directly to erosion and 

 deposition. If as an effect of erosion and 

 deposition an undertow is started tending 

 to reestablish the isostatie condition, this 

 undertow, a flow of material presumably 

 solid, necessarily develops considerable 

 heat by internal friction. The increase of 

 temperature so produced tends to cause 

 an increase of volume. It may favor new 

 chemical changes, including changes from 

 the solid to the liquid state, which may be 

 accompanied by a change of volume. The 

 undertow tends to be strongest not under 

 the region of rapid erosion nor under the 

 region of rapid deposition, but under the 



Horizontal compressive stresses in the 

 material near the surface above the under- 

 tow are necessarily caused by the under- 

 tow. For the undertow necessarily tends 

 to carry the surface along with it and so 

 pushes this surface material against that 

 in the region of erosion, see Fig. 2. These 

 stresses tend to produce a crumpling, 

 crushing and bending of the surface strata 

 accompanied by increase of elevation of 

 the surface. The increase of elevation of 

 the surface so produced will tend to be 

 greatest in the neutral region or near the 

 edge of the region of erosion, not under 

 the region of rapid erosion nor under the 

 region of rapid deposition. 



There has been indicated a complicated 

 set of changes of pressure, temperature 

 and density and of movements of material 

 beneath the surface, a set of changes which 



