THK CONTENTS OK THE SOIL 17 



'2. Ilnir Su;i /^ Mnh^ 

 2<l. T)i' iif'iijiiiiir >liin'iils 



'_'."». 'I'lie basis of soil is fra«::iii<Mits of rock. 

 To this base is a«Ul«Hl the remains of jihiiits and 

 animals (or organic matter) . When in <'<tn(]ition 

 to trntw plants, it also contains wati r. Tho 

 eharaettT of any soil, then'fort', is priniai-ily 

 (letermin<'<l by the kintl of I'ock from whicii it 

 has <*ome, and th** anionnt of oi-^'anir mattrr 

 and water whirh it contains. 



'_'(). As tin* surface of the earth co(»lrd, it 

 became rock-bound. Wiinkles an<l ridges ap- 

 peait'd, f(^rming mountains and valleys. The 

 tendcn«'V is for the elevations to be lessened an<l 

 the depressions to be filled. That is, the surface 

 of thf <'arth is bring leveled. The chief agency 

 in this leveling j)roceys is weathering. The hills 

 and mountains are worn down by alternations of 

 tcmp»'ratur«', by frost, ice, snow, rain an<l wind. 

 They art' worn away bv tln' loss of small par- 

 tich's : these particles, when gathered on the 

 hilUid«'>i or «leposite<l on lower levels, form soil. 



•J7. The Weathering agencies whi<'li re<lu<"e 

 the mountains operate also on level areas ; 

 but since the soil then remains wheie it is 

 forme«l, and thereby affords a ]>roteetion to 

 the underlying rock, the reduction of the ro<'k 



