138 NATURAL HISTORY oF THE FARM 



from the solid rock, p-ii\ity disposes of them: removes them 

 almost as fast as formed from the vertical face of the clifl: 

 lets them lie on the le\'cl summit: sweeps them do\\'n the 

 slope: spreads them out over the flood plain, making level 

 fields; or carries them far away with the rushing flood to 

 dump them into the bottom of the sea, where, removed from 

 light and air, they are lost to our use. 



Thus the rugged and geologically ancient outlines of 

 topography are softened by erosion and the more level 

 places are overspread by a mantle of productive soil. 

 Erosion roimds off the sharp edges of the headlands; 

 silting fills the low places; delta building covers the shores 

 about the mouths of streams; everywhere as time runs on, 

 sinuous lines replace the sharp angles, and verdure replaces 

 the gray pristine desolation. 



Let us go to some good point of outlook, some hill-top or 

 housetop or tower, and view the topography of our own 

 neighborhood, to see how the land lies. We will let oiu* eyes 

 wander slowly from the near-by fields upward to the summit 

 of the distant hills, and do^\Tlward to the level of the valley; 

 we will follow the stream that meanders across the valley 

 floor, back to its more turbulent tributaries, and on to the 

 little brooks that run among the hills. Upland and lowland 

 levels, and intervening slopes: — these are the natural divi- 

 sions of the land ; and their boundaries are all laid do\\Ti by 

 gravity. Water runs down hill, and loosened soil materials 

 move ever with it. They may glide unnoticed as tiny films 

 of sediment trickling between the clods of the fields ; or they 

 may move in great masses of earth and stone as a landslide, 

 scarring the face of the steep slope; but ever, with the aid of 

 water, they move to lower levels, and slowly the fonn of the 

 hill is changed. Flood-plains broaden: valleys are filled; 

 the slope grows gentler; and the upland plains are narrowed 

 by invading rills. 



