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JOHN ERNST WEAVER 



material from the exposed south and southwest slopes and de- 

 posited it upon the steeper north and northeast leeward slopes. 

 Table 2 gives the mechanical composition of the first foot of 

 soil on a northeast and southwest slope respectively. 



As is characteristic of dry regions, the transition from soil to 

 subsoil is not well marked, although the lighter colored subsoil 

 appears much nearer the surface on exposed than on sheltered 

 slopes. The humus content of the soils of north hillsides is 

 greater at all depths to 5 feet, in some cases more than 12% 

 greater, than on the exposed slopes, as was shown by six sets 

 of humus determinations made for each foot of soil on the two 

 slopes, respectively. This combination of more clay and more 

 humus on the north and northeast slopes reflects itself especially 



TABLE 2 



Mechanical composition of the firstfoot of prairie soils on a southwest and a north- 

 east slope respectively 



in the increased water-holding capacity of the soil. An average 

 of six determinations gave a mean water-holding capacity of 

 56% (based on dry weight at 104°C.) for the first foot of 

 soil on north slopes, as compared with 48% on south 

 slopes. This margin of 8% is rather an important difference 

 in favor of the soils on the protected slopes, since the wilt- 

 ing coefficients of the two soils differ but little. These sub- 

 stratum differences are pointed out here since it will be shown 

 later that certain plants are quite confined to moist north and 

 northeast hillsides. 



Studies of the water content of these soils have been carried 

 on since the spring of 1912. It will be unnecessary to burden 

 the reader with all of the data and graphs obtained, and only 

 enough will be given to make plain the seasonal march of soil 

 water. In figure 1 are graphs giving the march of soil water 

 from April 25 to September 25, 1913, on a typical northeast and 



