CJN DERTHRUSTING 



351 



ing of the same beds when they have become appressed and overturned. 

 The region to the right of Q would remain unfolded. 



The entire process would result in a typical folded belt in which the 

 intensity of plication and thrusting is probably proportionate to amount 

 of movement necessary to effect compensation; and this in turn is pro- 

 portionate to the mass transferred by erosion from the left to the right 

 of C ; that is, the most profoundly plicated and faulted mountains are 

 developed in regions of heaviest sedimentation, which is a fact well known 

 to geologists. 



It should be noted that the plication and thrusting can only proceed 

 while the deep compensatory current is flowing, thereby furnishing the 

 necessary stress; but so long as the current flows and underthrusting is 

 effected by rotation on PQ, a portion of the light rigid crust under PQ is 

 being pushed down into the heavier viscous subcrust, which, in so far as 

 it is not removed by the current, induces elevation of the surface of the 

 folded region by flotation. In this circumstance we have a probable ex- 

 planation of the uplift of folded regions into mountain ranges. This 

 elongation of the column under the folded belt necessitates, of course, a 

 displacement of the viscous layer at its base, thereby inducing currents 

 both to the right and the left of the folded region, the former eventually 

 neutralizing the causal current of the whole complex condition of strain 

 and so bringing the process to a close. 



It is further to be noted that the loading of the region CD determines 

 a tendency to uplift to the right of D as well as to the left of C, and that 

 underthrust movement induced by the viscous current implies a tensile 

 strain in the neighborhood of DH. Since, however, part of the mass that 

 moves from under CD flows to the right of D, the maximum tension is 

 probably located in depth between D and Q, and. this condition may ex- 

 plain the development of a batholithic magma in that region. 



