46 The Great World's Farm 



lingered and into which it drained from the surrounding 

 soil. Even when the water had drained away the hollows 

 would continue damp for some time, and grass-seeds fall- 

 ing upon them would readily spring up. The grass-plants 

 would speedily weave a network of roots over the whole, 

 forming in time a thick mat by which the soil would be 

 effectually held together and consolidated, and the bison 

 who wanted a dust bath in future would have to choose a 

 fresh wallowing place for himself and his companions. 



QUESTIONS FOR REVIEW 



1. Describe some of the plants which serve as soil-binders. 



2. What peculiar qualities has the mangrove? 



3. Give instances of the strength of these soil-binders. 



4. What result has often followed the cutting down of 

 mountain forests? 



5. What expedients have been used for checking both 

 snow and sand drifts? 



6. Describe the growth of grass in the bison country. 



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