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THE BOOK OF NATURE STUDY 



face is being denuded away, all kinds of scarp slopes will be in 

 slow retreat, but if the succession of rock-types remains constant, 

 their outlines will remain permanent in shape. In the case of 

 dipping strata the retreat will be in the direction of the dip of the 

 beds, and the features will tend to decrease in height as they retreat. 



FIG. 54. An anticline denuded by the sea as it rises, producing in succession the 



surfaces, aa, bb t cc^ dd. 



Retreat is more rapid than it would be if dependent on the resist- 

 ance of the hard bands alone, because the denudation of softer beds 

 underneath undercuts them. If retreat is unequal at various points 

 along the line of the scarp, as must be the case where counter-dip 

 streams run down it, portions will be left behind, at first as penin- 



FIG. 55. Plan and section of planed anticline with transverse streams, ab, ac, flowing 



across the strike of the beds. 



sulas, later as islands, of rock protected by a capping of the hard 

 bed (Fig. 52). The lower the angle of dip the more likely this is 

 to occur. These ^06-shaped hills capped by outlying patches of 

 hard rock are of frequent occurrence, and may sometimes be a long 

 way from the main outcrop of their protecting rock, indicating 



FlG. 56. Widening of transverse valleys when crossing soft beds. 



the enormous amount of material removed by denudation and 

 the profound results due to this agency. 



Plateaux are an extreme case of wold-hills where the dip 

 and consequently the " dip-slope " are horizontal. Their scarps are 

 often extremely steep, as shown by crowded contour-lines. On 



