CHAPTER XX.. Soils of the Arid and Humid Regions, 371.—Composition of

SOILS OF THE ARID AND HUMID REGIONS, 371.—Composition of Good Medium Soils; Table, 371.—Criteria of Lands of the Two Regions, 371.—Tables of Soil-Composition in Both Regions, 372.—Soils of the Humid Region governed by Time, 374.—Soils of the Arid Region Governed by Moisture, 374.—Lime and Magnesia Uniformly High in Arid Soils, Despite Scarcity of Limestone Formations; Potash also High, 374.—General Comparison of the Soils of the Arid and Temperate Humid Regions, 375.—Basis of Same, 376.—New Mexico and Analysis of Soil, 376.—General Table, 377.—Discussion of the Table, 378.—Lime; Summary of Physical and Chemical Effects of Lime Carbonate in Soils, 378.— Discussion of Summary, 379.—Magnesia: Its role in Plant Nutrition, 381.—Manganese: Its Stimulant Action, 383.—The “Insoluble Residue” or Silicates, 384.—Soluble Silica and Alumina, 384.—Analysis of Clay from Soil, 385.—Difference in Sand of Arid and Humid Regions. Table, 386.—Soluble Silica or Hydrous Silicates more Abundant in Arid than in Humid Soils, 388.—Aluminic Hydrate. Table, 389.—Retention of Soluble Silica in Alkali Soils, 391.—Ferric Hydrate, 392.—Phosphoric Acid, 392.—Sulfuric Acid, 394.—Potash and Soda, Retained more in Arid Soils, 394.—Arid Soils Rich in Potash, 395.—Humus, Low in Arid Soils, but Rich in Nitrogen, 396.—The Transition Region, 397.