Xli OUTLINE AND TABLE OF CONTENTS 



PAGE 



VI. Humid and arid soils 64 



VII. Resume 1 of scheme of classification and general char- 

 acteristics of the groups 66 



2. The soil mass. Physical properties of the soil and their 



modification 68 



a. Soil and subsoil (22). 



I. Inorganic constituents 69 



a. Texture (23). 



(a) Textural classification (24). 



(1) Textural groups (25). 



(2) Agricultural classes based on texture (26). 



(6) Some physical properties of arid and humid 

 soils (27). 



(c) Some properties of soil separates and classes 



(28). 



(1) Number of particles (29). 



(2) Surface area of particles (30). 



(3) Chemical composition of soil separates (31). 



(d) Modification of soil texture (32). 

 5. Structure (33). 



(a) Some aspects of soil structure (34). 



(1) Ideal arrangement (35). 



(2) Porosity (36). 



(3) Weight (37). 



(4) Plasticity (38). 



(5) Cementing materials (39). 



(6) Color (40). 



(7) Physical absorption (41). 



(b) Conditions affecting structure (42). 



(c) Means of modifying structure (43). 



(1) Variation in moisture content (44). 



(2) Formation of ice crystals (45). 



(3) Tillage (46). 



(4) Growth of plant roots (47). 



(5) Organic matter (48). 



(6) Soluble salts (49). 



(7) Animal life (50). 



(8) Rainfall (51), 



