I9I3-] SEE— ORIGIN OF HIMALAYA MOUNTAINS. 511 



and deposition. If as an effect of erosion and deposition an undertow is 

 started tending to reestablish the isostatic 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 in- 

 crease 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 

 deposition, but under the comparatively neutral region between the two in 

 which neither erosion nor deposition is much in excess of the other, see 

 Fig. 2. Hence the undertow by increasing the temperature and causing a 

 change of density may be "directly effective in changing the elevation of the 

 neutral region between two regions of deposition and erosion." 



BEeiON OF EROSION NEUTRAL REGION REOION OF DEPOSITION 



CiREATtST HORIZONTAL 



compression at sufifacc 



about hchc^ 

 /'oreatest meat tpom 

 [internal friction 



ABOUT HERE y 



DEPTH or OOMPrNSATION 



Fia. 2 



" Horizontal compressive stresses in the material near the surface above 

 the undertow are necessarily caused by the undertow. 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 accom- 

 panied 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." 



The criticism against this reasoning is the same as that used 

 above — namely, it will explain only balancing, but not the uplifting 

 of great mountain walls along the sea coast. Nothing but the 

 transfer of lava from beneath the sea, and the expansion of it 

 under the mountains will explain the observed mountain walls along 

 the borders of continents; and this requires positive forces of eleva- 

 tion, not mere negative processes. The advocates of isostasy, as 



PROC. AMEK. PHH.. SOC, UI. 211 O, PRINTED OCT. 3, I9I3 



