8 VERTICAL FARMING 



The Formation of Humus. The rock powder or meal does 

 not of itself make a desirable soil, and other matter must be 

 added. Microscopic plants must flourish to help in the work of 

 crop production ; water must be present, and as a rule, the more 

 humus the better the crops. This humus is not a strange sort 

 of stuff at all, as it is only rotten trash from dead plants or 

 animals. Mention has already been made of how its first start 

 is made. This is later augmented by the growth of larger 

 plants which have more leaves, twigs and roots to rot. In 

 increasing the amount of humus in a soil the work of man, 

 when intelligently applied, can be made to do wonders. 



GREEN MANURE CROP FOR INCREASING HUMUS 



How Soils are Moved. After the agencies just described 

 have ground out the rock powder, nature keeps right on at 

 work in moving and sorting out the soil particles. This work 

 is done by the action of : 



Gravity. The soils formed on the mountains and cliffs fall 

 to the base forming a heap of debris which is called " tallus." 

 Where the slope is steep, this falling is immediate ; but where 

 the land is more level, the movement is slower and is more of .a 

 slide than a fall. Gravity is ever at- work moving soils from 

 high to low levels. 



