ACKNOWLEDGMENTS 



The authors wish to acknowledge the originals of 

 the two colored maps as occurring in Bulletins 60 and 

 96 of the Bureau of Soils, U. S. Department of Agricul- 

 ture. The remaining illustrations were drawn es- 

 pecially for this text. Some few are copies in part, or 

 in whole, from other authors. Acknowledgments not 

 made in text are due the Bureau of Soils, U. S. De- 

 partment of Agriculture ; T. C. Chamberlin ; E. W. 

 Hilgard; F. H. King ; G. P. Merrill ; and H. W. Wiley. 

 The authors wisli also to express their appreciation to 

 Messrs. A. B. Beaumont and J. H. Bromley for their 

 careful work in the preparation of the original drawings 

 and to Miss Lela G. Gross for aid on the manuscript. 

 Thanks are also due Professor W. D. Bancroft for sug- 

 gestions as to the theoretical phases of soil colloids 

 and to Professor J. L. Stone for a like favor regarding 

 the soundness of the chapter on fertilizer practice. 



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