CONTENTS 



SOILS, THEIR ORIGIN AND CLASSIFICATION 

 CHAPTER PAGE 



INTRODUCTION ............................................ 1 



I. THE SOIL AND ITS ORIGIN ................................. 5 



1. Soil Defined. 2. Soil is Forming from Rock all the Time. 



3. The Weathering Agents: (a) Heat and cold, (6) frost, (c) 

 wind, (d) ice, (e) water, (/) gases; aided by other forces of 

 nature and by plants and animals. 4. Soil Formation Is a 

 Complex and Slow Process. 5. Most Soils are Carried Away 

 or Moved After They Form. 6. Soil of Many Kinds. 



II. SOIL COMPOSITION, CLASSES AND TYPES .................... 11 



1. Common Meanings of Soil and Subsoil. 2. The Compo- 

 sition of Soil: (a) Mineral particles sand, silt, clay from 

 rock, (b) Organic matter remains of plants. 3. Soil a 

 Complex Medium for Plant Growth : (a) Sand, silt, clay con- 

 stitute the framework and contains : (6) water (moisture) ; 

 (c) soil organisms; (d) air; (e) salts in greater or less amounts. 



4. Soil Classification: (a) On the basis of texture (grouped 

 into classes) : sand, fine sand, sandy loam, fine sandy loam, 

 loam, slit loam, clay loam and clay, (b) On the basis of mode 

 of formation: residual, cumulose, alluvial, glacial, marine, 

 lacustrine, loess and colluvial. (c) On the basis of types 

 (grouped into series): Dunkirk sand, Genesee loam, Knox 

 silt loam, Cecil loam, etc., as types. 



SOILS FROM A CHEMICAL POINT OF VIEW 



III. CHEMICAL COMPOSITION OF SOILS AND ITS RELATION TO PLANTS 



AND ANIMALS ..... .................................. 29 



1. Soil Materials are Composed of Elements. 2. Chemical 

 Composition of Soils. 3. The Fertilizing Elements Nitro- 

 gen, Phosphorus and Potassium. 4. The Supply of the 

 Important Elements in Soils not Large. 5. Chemical Com- 

 position of Soils Influences Plant Growth. 6. Crops 

 Require Ten Elements C, H, O, P, K, N, S, Ca, Fe, Mg. 

 7. Sources of Elements Plants Require: (a) The soil 

 nitrogen and mineral elements; (b) The soil water oxygen 

 and hydrogen; (c) The air carbon and oxygen. 8. Ash of 

 Animal Body is "Dust" of the Earth. 9. The Great Work 

 of Plants and the Farmer's Business. 



IV. How ROCKS AND CLIMATE AFFECT SOILS ................... 39 



1. Rocks of Many Kinds, and They Undergo Changes. 



2. A Rock is an Aggregate of Mineral Particles. 3. Rock 

 Minerals the Sources of Mineral Plant-food Elements. 

 4. The Relation Between the Presence of Particles of Rock 

 Minerals and the Richness of Soils. 5. Products of Rock 

 Weathering: (a) Sand, silt, clay breaking-up products; 

 (6) True clay (kaolin), (c) Carbonate of lime, (d) Salts. 

 6. Different Soils from Different Rocks. 7. The Effect of 

 Climate on Soils: (a) Soils in humid regions are leached. 

 (6) Alkali soils formed in dry regions, (c) Much organic 



xi 



