CHAPTER XXI.. Soils of Arid and Humid Regions Continued, 398.—_soils of the

SOILS OF ARID AND HUMID REGIONS CONTINUED, 398.—Soils of the Tropics, 398.—Humus in Tropical Soils, 399.—Investigations of Tropical Soils, 401.—Soils of Samoa and Kamerun, 402.—Soils of the Samoan Islands, 403.—Soils of Kamerun, 404.—Soils of Madagascar, 405.—Soils of India, 410.—The Indo-Gangetic Plain, 411.—The Brahmaputra Alluvium in Assam, 413.—Black Soils of Deccan, 414.—Red Soils of the Madras Region, 415.—Laterite Soils, 416.—Influence of Aridity upon Civilization, 417.—Preference of Ancient Civilizations for Arid Countries, 417.—Irrigation Necessitates Co-operation, 419.—High and Permanent Productiveness of Arid Soils Induces Permanence of Civil Organization, 419.