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National GeograjpMc Magazine. 



of D is retarded by its having to join the main stream at a point 

 where the hard bed in the axis of the fold holds the main channel 



well above baselevel. The notch cut by D will then be changed 

 from a water-gap to a wind-gap and the upper portion of D will 

 findfexit through the notch cut by C, as in fig. 11, As other sub- 

 sequent headwaters make capture of C, the greater depth to which 

 the lateral valley is cut on the soft rock causes a slow migration 

 of the divides in the abandoned gaps towards the main stream, 

 and before long the upper part of the main stream itself will be 

 led out of the synclinal axis to follow the monoclinal valley at 

 one side for a distance, fig. 12, until the axis can be rejoined 

 through the gap where the axial portion of the controlling hard 

 bed is near or at baselevel. The upper part of the synclinal 

 trough will then be attacked by undercutting on the slope of the 

 quickly deepened channels of the lateral streams, and the hard 

 bed will be worn away in the higher part of the axis before it is 



