. Elementary physical geography . ,) -y 368 PHYSICAL GEOGRAPHY. peaks lose in elevation, the ridges are worn down, the streamshave chosen the softer layers for their valleys, and the aspectof the mountains has become quite changed. This is the stagewhich has been reached by the Appalachians. These moun-tains were once much higher than now; and since they havelong been exposed to the destructive action of weatheringand erosion, they have lost their ruggedness, and are strik-. MlatiS **«*_ Fig. mountain ridge in Colorado, showing hard layers etched into relief. ingly in contrast with such
. Elementary physical geography . ,) -y 368 PHYSICAL GEOGRAPHY. peaks lose in elevation, the ridges are worn down, the streamshave chosen the softer layers for their valleys, and the aspectof the mountains has become quite changed. This is the stagewhich has been reached by the Appalachians. These moun-tains were once much higher than now; and since they havelong been exposed to the destructive action of weatheringand erosion, they have lost their ruggedness, and are strik-. MlatiS **«*_ Fig. mountain ridge in Colorado, showing hard layers etched into relief. ingly in contrast with such as the Rockies, the Himalayas,and the Alps, which are examples of young mountains. This action of destruction may be carried beyond the stagereached in the Appalachians, and whole mountain chainsmay be worn down to their very roots, and reduced to aseries of relatively low hills. The highland portions of NewEngland, New Jersey, and the entire region from this state PLATEAUS AND MOUNTAINS. 369 to the Carolinas, east of the base of the Appalachians, repre-sents such an old mountain range. As a result of this mountain destruction, many interestingchanges are brought about; but the most striking result isthe etching of the surface, so that everywhere the elevationsare those of hard rocks, while the depressions occur in thesoft strata. At first the mountain ridges may have had fortheir surface rock some soft layer which was bent up intoa ridge (Fig. 262). But after lon
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