510 SEE— ORIGIN OF HIMALAYA MOUNTAINS. [April i8. 



be maintained ; but it is not possible to account for the origin of the 

 inequalities of level. Isostacy as thus depicted is not an active 

 creative agency, but simply a negative process for maintaining exist- 

 ing inequalities. Under the doctrine as above stated, the height of a 

 mountain or plateau could never increase, for that would require 

 the exertion of positive elevating forces, not mere balancing for 

 maintaining inequalities of levels already existing. 



Accordingly, this formulation of the doctrine of isostacy is de- 

 fective, and inadequate to account for the phenomena of the earth's 

 crust. 



The true doctrine should include not only the balancing process 

 described by Hayford, but also those elevating forces directed from 

 the sea, by which the mountains are elevated as narrow walls about 

 the borders of continents, on the great plateaus which spread out as 

 wider embankments beneath them. Without these positive uplifting 

 forces, no continent could ever have a mountainous border thrown 

 up about it. 



No doubt the elevation is produced under approximately isostatic 

 conditions. Mountains can be forced up only to a certain height, 

 the transfer of lighter material under the higher parts thus giving 

 nearly equal mass in all equal prisms drawn to the center of the 

 earth. The path of least resistance is towards regions of elevation, 

 and the underlying material expands as the surface level is forced 

 up. If this were not so the greater weight under the elevated region 

 would cause it to subside to the common level. In this way, and 

 in this way only, can progressive elevation be produced. 



The weakness of the old method of reasoning is further illus- 

 trated by Hayford's remarks : 



" Under a region of deposition two effects of opposite sign tend to occur. 

 The effect of increased pressure tends to produce chemical changes accom- 

 panied by decrease of volume and so to produce a sinking of the surface. 

 The blanket of deposited material tends to raise the temperature 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 to arrest the 

 subsidence caused by increased pressure or even to raise the surface and 

 change the region of deposition into one of erosion." 



" The changes of temperature just described are due directly to erosion 



