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N order to understand the nature of soils thoroughly, some 

 knowledge of geology, mineralogy, chemistry, and physicsr 

 is necessary. Geology and mineralogy teach the origin, 

 chemistry and physics, the composition and functions of 

 soils ; and when these aspects have been studied, climate 

 and all surrounding conditions must be taken into account 

 before we can be in possession of full information. 



The subject may be usefully divided into the following 

 sections : (1) ORIGIN, (2) FORMATION, (3) DISTRIBUTION, (4) 

 PHYSICAL PROPERTIES AND SURROUNDING CONDITIONS, (5) CLASSIFICA- 

 TION. 



1. ORIGIN OF SOILS. 



As a primary fact, it may be stated that the entire mineral matter of 

 soils has been derived from the gradual decay or disintegration of rocks. 

 It is usual to state that soils are derived from the decay of the crystalline 

 (primitive) rocks, because from them all intermediate and newer rocks 

 have been derived. 



This decay has been effected during the lapse of long ages, by means of 

 natural forces still in active operation, as may be seen in the crumbling 

 of building stones, and that " weathering " which gradually changes the 

 hardest rock into a powdery mass. Changes of temperature, operating 

 with ^vater, in the many forms assumed by that element, the action of the 

 atmosphere and vegetation, are the chief causes of decay ; and to these may 

 be added volcanic action, which, as is well known, is the cause of the rapid 

 formation of new and fertile lava soils. 



In dry climates, where rain seldom falls, inscriptions upon stones retain 

 their freshness for thousands of years, thereby proving the extreme dura- 

 bility of certain rocks when favourably situated. On the other hand, in 

 a humid atmosphere, decay progresses much faster, as may be noticed in 

 the crumbling condition of ruins, and even more recent buildings. Dur- 

 ing certain geological epochs, the surface of our planet has been exposed 

 to conditions of heat and moisture highly favourable to the decay of rocks ; 

 and under those conditions, thick beds of granite, yielding to the in- 



