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CONTENTS 



The study of heat, 

 air, oxygen, carbon di- 

 oxide, running water, 

 freezing water, solu- 

 tions, atmospheric mois- 

 ture, evaporation, and 

 condensation in previ- 

 ous chapters now en- 

 ables the pupil to un- 

 derstand how the earth 

 has been shaped and 

 how its rocky surface 

 was gradually pulver- 

 ized into soil. 



The chapter on the 

 origin of soil is logi- 

 cally followed by a 

 study of man's use and 

 conservation of soils. 



Since light is neces- 

 sary to life, this chapter 

 on light supplements 

 the preceding chapter, 

 and prepares for the 

 study of life in the next 

 chapter. 



CHAPTER IX. THE EARTH'S CRUST 



Changes in the Earth's Condition Materials 

 Composing the Land Upward and Down- 

 ward Movements of the Earth's Crust Hills 



Mountains Plateaus Plains . . 247 



Continental shelf. Newfoundland banks. Reefs 

 and dunes. Buttes and mesas. Erosion. 



CHAPTER X. PREPARATION OF THE EARTH'S 

 SURFACE FOR PLANT LIFE 



Natural Forces Weathering The Work of 

 Wind, Ice, and Snow Glaciers and Icebergs 



The Glacial Period Glacial Formations 

 and Lakes Prairies of the United States 

 Production of Soils . . . . .277 



Soils produced by weathering. Ice as a soil- 

 builder. Parts of our country once covered by ice. 



CHAFIER XI. MAN'S USE AND CONSERVA- 

 TION OF SOILS 



Importance of the Soil Composition of the 

 Soil Water Film on Soil Particles Fertile 

 Soil Fertilizers New Sources of Potash 

 Fertilizing Agents : Gophers, Moles, Angle- 

 worms, Bacteria Agricultural Soils Soil 

 Water Water-plants Dry Farming Irri- 

 gationAlkali Soils Value of Soils Rec- 

 lamation Projects Forestry . . . 307 



Soil air. Humus. The work of moles, angle- 

 worms, and bacteria. Sand, silt, and clay. 

 Drainage and'seepage. 



CHAPTER XII. THE SUN'S GIFT OF LIGHT 



Light Necessary to Life Direction, Intensity, 

 Reflection, and Speed of Light Refraction 

 of Light : Telescope, Color Light aiid Com- 

 fort . . . . . . .347 



.Lenses and cameras. Microscope, telescope, arid 

 spectroscope. Light and health. Natural and 

 artificial lighting. 



