74 AGRICULTURE. 



soil is reduced to too fine a dust, for it is apt 

 to puddle when it rains, and exclude the air. 

 Tillage also keeps down the weeds, which would 

 rob the soil of plant-food and exclude heat and 

 light. 



C. REFERENCES FOR CHAPTERS I., II., AND III. 



" Systems of Farm Management in the United States." Year- 

 book, 1902. 



"The Movement and Retention of Water in Soils." 



"Some Interesting Soil Problems." Year-book. iS<.,j. 



" Origin, Value, and Reclamation of Alkali Lands." Year- 

 book, 1895. 



" Reasons for Cultivating the Soil." Year-book, 1895. 



" Irrigation for the Garden and Greenhouse." Year-book, 

 1895. 



"Soil Investigations in the United States." Year-book, 1899. 



"Some Important Soil Formations." Bulletin 5, 1896, Division 

 of Agricultural Soils, United States Department of Agriculture. 



"Soil Solutions." Bulletin 17, Division of Soils, United States 

 Department of Agriculture. 



" Instruction in Agronomy at Some Agricultural Colleges." 

 Bulletin 127, Office of Experiment Station, United States Depart- 

 ment. 



" Bulletin 41, 1893," Minnesota Agricultural Experiment 

 Station. 



" The Soil." King. 1900. 10. 



" Soils and Crops." Morrow & Hunt. 1902. 4. 



" Manual of Geology." Dana. 1895. 



" Physical Geography." Gilbert & Brigham. 1902. I. 



" An Introduction to Geology." Scott. 1897. 10. 



" Geology." Brigham. i. 



