49 



Piscussion. The amounts of magnesia found on the two drifts 

 are very similar, the averages for the three foot section on the Kansan 

 and the Late Wisconsin, respectively, heine; 0.98 per cent and 0.99 per 

 cent. Considerahle variation from type to ty])e is shown, the Farp^o 

 silt loam carrying the most and the Carrington loam the least. 



The ratio of total lime to magnesia is slightly the hig^her on the 

 Late Wisconsin, this heing due to its higher proportion of the former 

 constituent. 



'{"he average ratio of lime as silicate to magnesia is very similar 

 on both drifts with the exception of that for the Ivargo silt loam on the 

 Late Wisconsin, where it is somewhat the lower. The maximum ratio 

 in every instance is found in the surface section while the minimum is 

 found in the third foot, except on the Carring:ton loam, where it 

 appears in the second foot-section. 



8, Phosphoric Acid. 



The phosphoric acid (Tables 45 to 48) was determined in all the 

 field samples bv the modification of Washington's method described 

 above (p. 41). Averages from these give the data for the drift 

 samples (Table 49). 



Carrington Silt Loam. On this type (Table 45) there is shown, 

 in general, a decrease from the surface downward, a distribution char- 

 acteristic of prairie soils (3). The amount found on the Kansan is 

 slightly higher than that on the Late Wisconsin, the general average 

 for the former being 0.165 per cent compared with 0.141 for the latter. 

 The distribution from field to field is very regular. 



Fargo Silt Loam. While somewhat larger amounts of phosphoric 

 acid are found in the soils of this type (Table 46), the same observ^a- 

 tions as to its distribution apply. 11ie difiference in the amounts found 

 on the two drifts are, however, much greater, the average for the 



