CHAPTER I. 



NATURE AND FORMATION OF SOILS. 



SOIL is derived, primarily, from rock * in the 

 broadest sense of the term. The cycle of tear- 

 ing down in one place and building up in an- 

 other has been constantly going on for ages, 

 and is still going on to-day. It is to this cycle 

 of changes, discussed in the following pages, 

 that we owe the presence of the loose surface 

 material of the earth (some places a few hun- 

 dred feet in depth, and in some places entirely 

 wanting) which makes it possible for plants and 

 animals to live, and which loose material forms 

 the basis of all soil. 



A. SOURCES OF ENERGY. 



The matter which constitutes the earth and 

 atmosphere, though it cannot be destroyed, is 

 constantly changing its form, under the action 

 of existing forces. The sources of all these 

 forces, or of our supply of energy, are the earth 

 and the sun. 



I. The Earth's Energy. 



The earth's energy is from within, and some 

 of its manifestations are the upheavals and dis- 

 ruptions of the crust, and, greatest of all, the 



*"Any substance constituting a portion of the earth's crust 

 ... is called a rock." Leconte's Commend of Geology, p. 178. 



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