CONTENTS. xiii 



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 ; Sum- 

 mary 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 Res- 

 idue" 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. 



CHAPTER XXI. 



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 Al- 

 luvium 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 Coun- 

 tries, 417. Irrigation Necessitates Co-operation, 419. High and Per- 

 manent Productiveness of Arid Soils Induces Permanence of Civil 

 Organization, 419. 



CHAPTER XXII. 



ALKALI SOILS, THEIR NATURE AND COMPOSITION, 422. Alkali Lands vs. 

 Seashore Lands, 422. Origin, 422. Deficient Rainfall, 423. Predom- 

 inant Salts, 423. Geographical Distribution, 424. Their Utilization of 

 World-wide Importance, 424. Repellent Aspect, Plate, 424. Effects of 

 Alkali upon Culture Plants. Figures of Apricot Trees, 426. Nature of 

 the Injury, External and Internal, 426. Effects of Irrigation, 428. 

 Leaky Irrigation Ditches, 429. Surface and Substrata of Alkali Lands, 

 429. Vertical Distribution of the Salts in Alkali Soils, 429. How 

 Native Plants Live, 430. Figures of various Phases of Reclamation, 

 431. Upward Translocation from Irrigation, 433. Distribution of Al- 

 kali in Sandy Lands, 433. In Heavier Lands, 436. Salton Basin or 

 Colorado Delta, 436. Diagram of Alkali Distribution in Same, 438. 

 Horizontal Distribution of Alkali Salts in Arid Lands, 439. Alkali in 

 Hill Lands, 439. Usar Lands of India, 440." Szek " Lands of Hungary, 

 440. Alkali Lands of Turkestan, ^.Composition and Quantity of 

 Salts Present, 441. Nutritive Salts, 441. Black and White Alkali. 

 Tables, 442. Estimation of Total Alkali in Land, ^.Composition of 



