150 LANDSCAPE DESIGN 



designer can observe what typical forms his material would take under 

 the natural forces at work in the surrounding landscape, and what forms 

 it actually does take in the surfaces immediately adjacent to his work. 

 He can then arrange his slopes so that at least they may be of a general 

 form similar to those found in the locality, and of a sequential and smooth 

 flow of surface, continuous with that of the forms into which they should 

 merge. A judicious choice of variety in form and steepness of slope, 

 special care in the junction of the new surfaces with the old, and stu- 

 dious avoidance of unduly symmetrical forms or straight lines or sharp 

 angles at least when dealing with soft materials will produce a 

 form unity between the designer's work and the landscape which will 

 go a long way towards unifying the composition which includes both. 

 It should be said, too, that the natural forms of earth surface are 

 those which are assumed by the particular material in accord with all 

 the natural forces at work gravitation, rain-wash, etc. and these 

 forms are therefore in most cases changing but slowly. Imitations of 

 these forms therefore would presumably be stable if made of the same 

 material. The greatest steepness of a bank will be fixed by the angle 

 of stability of its component material under the forces to which it will 

 be exposed. An earth bank subject to the erosion of running water 

 will practically never reach an angle of repose, and must be protected 

 by some erosion-resisting surface. An earth bank which may at times 

 be very wet, though not actually eroded, will still tend to assume a low 

 angle of repose, and may have to be held in place by the roots of vege- 

 tation or by bowlders. In general, the choice of form and slope at the 

 disposal of the designer in any particular case will be restricted, not only 

 by geologic congruity to natural form and by compositional form unity 

 with the surrounding forms, but also by the physical characteristics 

 of his materials. 



