Page:Tree Crops; A Permanent Agriculture (1929).pdf/345

 . 120. Top. A mangum terrace. Man at left stands upon its crest. Man at right shows where water flows away across field. (Courtesy Agr. Ex. Sta. Univ. of Ill.)—. 121. Center. This typical Old World terrace from the Apennines of Italy prevents erosion at the price of much hand labor. Machinery can cross the device shown in Figs. 114 and 120. (Photo J. Russell Smith.)—. 122. Bottom. Black Belt of Alabama. Shallow soil, one of best in the world, washed away to bedrock of white limestone in a few decades. (Courtesy U. S. Dept. Agr.)