CHAPTER II 



THE PHYSICAL CHARACTER OF SOILS 



THE earthy covering over the rocks, which we 

 call soil, being largely composed of the particles 

 of the rocks themselves, varies greatly in its 

 texture or physical composition. Since its first deposition 

 this soil has been the great laboratory of nature in which 

 many and great chemical and physical changes have been 

 brought about. And in this great laboratory the work 

 has never ceased. It is still in progress, through agencies 

 which may be classed as physical, chemical, and biologi- 

 cal, as we shall see. 



There is a wide difiference, as the most 

 The Soil's casual observer may note, in the size of the 

 M(Ssture particles that make up our soils, and this 



difference in size involves also a great differ- 

 ence in the capacity of different soils for the retention of 

 moisture. In soils that are sufficiently well drained for 

 agricultural purposes the moisture does not exist as stand- 

 ing water; and this is essential since the welfare of all our 

 cultivated plants demands free access of air. It is moist 

 air rather than water which plant roots need, and this 

 moist air is secured by the dehcate films of water that sur- 

 round and adhere to each particle of the soil. 



It will be easy, then, to realize that the smaller these 

 particles, each with its delicate film of water, the greater 



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