CONTENTS. vii 



of these Deposits, 70. Nature of the Salts, 71. Kainit, 71. Potash 

 Salts in Alkali Soils, 72. Farmyard or Stable Manure ; Chemical 

 Composition, Table, 72. Efficacy largely due to Physical Effects in 

 Soils, 73. Green-manuring a Substitute for Stable Manure, 74. Ap- 

 plication of Stable Manure in Humid and Arid Climates, 74. Mine- 

 rals Unessential or Injurious to Soils, 75. Iron Pyrites, Sulphur Balls, 

 75. Occurrence and Recognition. Remedies 75. Halite or Common 

 Salt, 76. Recognition of Common Salt, 76. Mirabilite or Glauber's 

 Salt ; in Alkali Lands ; not very Injurious, 77 Trona or Urao ; Car- 

 bonate of Soda, "Black Alkali," 77. Injury Caused in Soils, 78. 

 Epsomite or Epsom Salt, 78. Borax, 79. Soluble Salts in Irrigation 

 Waters, 79. 



CHAPTER VI. 



PHYSICAL COMPOSITION OF SOILS, 83. Clay as a Soil Ingredient, 83. 

 Amounts of Colloidal Clay in Soils, 84. Influence of Fine Powders on 

 Plasticity, 85. Rock Powder ; Sand, Silt and Dust, ^. Weathering 

 in Humid and Arid Regions, 86. Sands of the Humid Regions, 86. 

 Sands of Arid Regions not Sterile, 86. Physical Analysis of Soils, 88. 

 Use of Sieves. Limits, 88. Use of Water for Separating Finest Grain- 

 Sizes, 89. Elimination of Clay by Subsidence and Centrifugal Method, 

 Hydraulic Elutriation, 90. Schone's Instrument, 90. Churn Elutriator 

 with Cylindrical Tube, 91. Figures of Same, 91. Voder's Centrifugal 

 Elutriator, 92. Number of Grain-sizes Desirable, 93, Results of such 

 Analyses, 93. Physical Composition Corresponding to Popular Desig- 

 nations of Soil-Quality. Table, 96. Number of soil-grains per Gram, 

 99. Surface Offered by various Grain-sizes ,99. Influence of the several 

 Grain-si/.es on Soil Texture, 100. Ferric Hydrate, its Effects on Clay, 

 loo. Other Substances, ioi. Aluminic Hydrate, 101. Influence of 

 Granular Sediments upon the Tilling Qualities of Soils, 102. " Phy- 

 sical " Hard pan, 103. Putty Soils, 103. Dust Soils of Washington ; 

 Table, Physical Analyses of Fine Earth, 104. Slow Penetration of 

 Water, 105. Effects of Coarse Sand, 105. 



CHAPTER VII. 



DENSITY, PORE-SPACK AND VOLUME-WEIGHT OF SOILS, 107. Density of 

 Soil Minerals, 107. No Great Variation, 107. Volume-weight most Im- 

 portant, 107. Weight per Acre-foot, 107. Air-space in Dry Natural 

 Soils. Figure, 108. May be Filled with Water, 108. Effects of Tillage. 

 Figures, 109. Crumb or Flocculated Structure ; Cements, 109. How 

 Nature Tills, ill. Soils of the Arid Regions; do not Crust, 112. 

 Changes of Soil-Volume in Wetting and Drying, 112. Extent of 

 Shrinkage, 113. Expansion and Contraction of Heavy Clav Soils. 

 Figure, 113. Contraction of Alkali Soils on Wetting, 114. "Hog 

 Wallows," 114. Physical Analyses of such Soils. Table, 115. Crumb- 

 ling of Calcareous Clay Soils on Drying, 116. Yazoo Bottom, Port 

 Hudson Bluff, 116. Loamy and Sandy Soils, 117. Formation of Sur- 

 face Crusts, Physical Analyses, 117. Effects of Frost on the Soil; 

 Heaving; Ice-flowers, 118. 



