Transcriber’s Notes: Underscores “_” before and after a word or phrase indicate _italics_ in the original text. Small capitals have been converted to SOLID capitals. Illustrations have been moved so they do not break up paragraphs. Old or antiquated spellings have been preserved. Typographical and punctuation errors have been silently corrected. SOILS [Illustration: ·The MM Co·] THEIR FORMATION, PROPERTIES, COMPOSITION, AND RELATIONS TO CLIMATE AND PLANT GROWTH IN THE HUMID AND ARID REGIONS BY E. W. HILGARD, PH.D., LL.D., PROFESSOR OF AGRICULTURE IN THE UNIVERSITY OF CALIFORNIA, AND DIRECTOR OF THE CALIFORNIA AGRICULTURAL EXPERIMENT STATION New York THE MACMILLAN COMPANY LONDON: MACMILLAN & CO., LTD. 1921 COPYRIGHT, 1906, BY THE MACMILLAN COMPANY. Set up and electrotyped. Published July, 1906. Norwood Press: Berwick & Smith Co., Norwood, Mass., U.S.A. SUMMARY OF CHAPTERS. 1. ORIGIN AND FORMATION OF SOILS. Introduction. Chapter I. Physical Processes of Soil Formation. “ II. Chemical Processes of Soil Formation. “ III. Chief Soil-forming Minerals. “ IV. The Various Rocks as Soil-Formers. “ V. Minor Mineral Ingredients of Soils. Mineral Fertilizers. Minerals Injurious to Agriculture. 2. PHYSICS OF SOILS. Chapter VI. Physical Composition of Soils. “ VII. Density, Pore Space, and Volume-Weight of Soils. “ VIII. Soil and Subsoil; Causes and Processes of Differentiation; Humus. “ IX. Soil and Subsoil; Organisms Influencing Soil-Conditions. Bacteria. “ X. Soil and Subsoil in their Relations to Vegetation. “ XI. Water of Soils; Hygroscopic and Capillary Moisture. “ XII. Water of Soils; Surface, Hydrostatic, and Ground water; Percolation. “ XIII. Water of Soils; Conservation and Regulation of Soil Moisture. Irrigation. “ XIV. Absorption by Soils of Solids from Solutions. Absorption of Gases. The Air of Soils. “ XV. Colors of Soils. “ XVI. Climate. “ XVII. Relations of Soils and Plant-Growth to Heat.