244 ROLLIN T. CHAMBERLIN 



Bridge and the Grand Hogback, constitute in reality a plateau 

 region rather than a folded mountain area. This strip is to be 

 considered the southeastern extension of what has been called the 

 White River plateau. In fact the deformation in the westernmost 

 forty miles of the chosen section was so slight that this strip was 

 not originally included in the folded mountain section measured in 

 1915. It was added in 1916. Fig. 13 indicates that beneath this 

 region of plateau-like uplift the lateral thrusting movement has 

 been distributed through a thick zone which has been deformed only 

 slightly. 



To interpret Fig. 13 the deforming movement pictured as the 

 result of thrusting from the west was distributed at first through 

 a thick shell in the plateau region, but in this thick zone it reached 

 only a low degree of intensity. The region was in consequence but 

 feebly wrinkled. But in the region next east, where the Grand 

 River today turns abruptly northwestward near State Bridge, the 

 activity was concentrated in a thinner movable zone which was 

 far more sharply folded. This marks the western flank of the 

 folded belt which culminated in the Gore or Park Range. Next 

 east of this, less folding in the middle of the Gore Range indicates 

 greater depth of shell there, followed by thinning again on the 

 eastern flank of the Gore Range. The disturbed mass became 

 thinner again in the Middle Park region, where the uplifting was 

 relatively less, and then it deepened rapidly beneath the Front 

 Range, where the uplift was greater, again thinning out rapidly to 

 the edge of the Great Plains, which border the folded belt on the 

 east. In this way the Front Range repeated the wedge-shaped 

 block of the Park Range. 



These results are based on the assumption that the shortening 

 has remained the same throughout the full depth of each deformed 

 block. If the shortening, in reality, increases with depth these 

 figures are overestimates of the thickness of the folded shell. But 

 on the other hand, if it be true that there was less folding and less 

 shortening in the deeper portions of these blocks, these figures are 

 underestimates of the depths to which the folding extended. Of 

 the two alternatives the latter seems the more probable. With 

 increasing depth below the surface, the resistance of the rocks to 



