Evolution of Soils. 177 



stance over the rock, sending its fibers into the 

 crevices and filling the chinks, as they enlarge, with 

 the decay of its own structure ; and finally the 

 rock is fit for the moss or fern or creeping vine, each 

 newcomer leaving its impress by which some later 

 newcomer may profit. Finally the rock is disinte- 

 grated and comminuted, and is ready to be still 

 further elaborated by corn and ragweed. Nature 

 intends to leave no vacant or bare surfaces. She 

 providently covers the railway embankment with 

 quack -grass or willows, and she scatters daisies in 

 the old meadows where the land has grown sick 

 and tired of grass. If one pulls up a weed, he 

 must quickly fill the hole with some other plant, or 

 nature will tuck another weed into it. Man is yet 

 too ignorant or too negligent to care for the land, 

 and nature must still stand at his back and sup- 

 plement the work which he so shabbily performs. 

 She knows no plants as weeds. They are all 

 equally useful to her. It is only when we come to 

 covet some plant that all those which attempt to 

 crowd it out become weeds to us. If, therefore, we 

 are competent to make a choice of plants in the first 

 place, we should also be able to maintain the 

 choice against intruders. It is only a question of 

 which plants we desire to cultivate. 



We must keep the land at work, for it grows 

 richer and better for the exercise. A good crop on 

 the laud, aided by good tillage, will keep down all 

 weeds. The weeds do not "run out" the sod, but 

 the sod has grown weak through some fault of 



