VERTICAL FARMING 



U.S.G.S. 



THE MOVEMENT OF SOIL FORMING MATERIAL BY GRAVITY. 



Water. Every drop of water that falls on the earth can 

 move a particle of soil at least a little distance. These drops 

 of rain run together to form rivulets, each with its little load 

 of soil. Rivulets meet to form streams, and these join to form 

 creeks, and the creeks unite to form rivers. A creek or river 

 in flood-time is a stream of soil moving down from the factory 

 to be spread out over distant valleys and plains, or to fill up the 

 bottom of the sea so that it can finally be used by man to grow 

 food and raiment. 



Glaciers. The great sheets of ice that have already been 

 described moved great distances, and carried with them large 

 amounts of soil and soil material. Some of them moved from 

 Canada into what is now the United States, and brought fertile 

 material far within our borders to make some of the richest 

 land in the world. 



Winds. The housekeeper knows how fast dust accumu- 

 lates over everything, and how it thickens on furniture and 

 carpets if left undisturbed for even a short time. The winds 



