42 



DRY FARMING 



Valley of the North are typical examples, the latter 

 being at one time the bed of the old Lake Agassiz. 



30. Soil Types. — Soils are further divided into types 

 depending upon the content of the various soil ma- 

 terials. Thus we have gravels, sands, silts, clays, 

 gravelly loam, sandy loam, silt loam, clay loam, muck, 

 peat and loam. By a loam is meant a soil having a good 

 balance of the various constituents, that is, not enough 

 clay to render it plastic, not enough sand to make it too 

 loose and open, and with a sufficient supply of organic 



Fig. 18. — Soil Surface Map of Iowa. 



The soils in each county in most of the States are being mapped anc 

 classified and the local agricultural conditions studied in order that intelli 

 gent direction may be offered farmers for increasing production. Th( 

 problems of Western Canada need such a systematic study. — Courtesy o! 

 the Iowa Experiment Station. 



matter to give a good friable texture. The percentage of 

 various soil materials determines the physical character 

 of the soil, i. e. the texture, the ease of cultivation, the 



