J. Hendrick and W. G. Ogg 467 



Plains differ greatly as a class from the Residual and Glacial Soils. 

 These differences are dealt with in detail in the original memoir. In 

 order to illustrate the general effects on the composition of their 

 differences in origin we have calculated the average composition of the 

 separates of the three groups of soils, and the results are shown in 

 Table V. 



This Table is not given in the original bulletin of Failyer, Smith 

 and Wade, but has been calculated from the figures given in their 

 detailed tables. 



Summarising their work, Failyer, Smith and Wade point out: 



1. That ''as a general rule, the smaller particles of soils are richer 

 in potassium, calcium, magnesium, and phosphorus than the larger 

 particles." 



2. That "the concentration of these elements in the finer com- 

 ponents is the more pronounced as the soils have undergone more 

 extreme weathering." 



3. That " in glacial soils and others resulting largely from mechanical 

 processes, the coarser particles are relatively high in the percentages 

 of potash, lime and magnesia." 



Comparing British soils in the same way we find a somewhat similar 

 contrast in the composition of the fractions according to the origin of 

 the soil. A number of English soils from the gault, bargate, brick 

 earth, and clay with flints formations were fractionated and the 

 fractions were analysed by Hall and RusselP. The average of these- 

 may be taken to represent the much weathered and decomposed 

 minerals of the soil of the South of England as contrasted with the 

 granitic and metamorphic glacial drift of the north-east of Scotland, 

 which though pulverised by glacial action has not undergone the 

 age-long weathering processes of the southern English soils. 



In Table VI we have placed side by side our analyses of the 

 fractions of Craibstone soil and the average of the analyses of similar 

 fractions of English soils in order to illustrate the striking differences 

 between the constitution of these two classes of soils. Hall and Russell 

 divide the "fine silt" in their analyses into two parts, shown as (a) 

 and (b) in Table VI. {a) consists of particles from -01 to -005 mm. 

 in diameter, while (b) consists of particles from -005 to -002 mm. in 

 diameter. They also give two sets of figures for "clay," shown in Table 

 VI as (c) and (d). Under (c) is given the analysis of clay from 



' Jour. Agri. Sci. 1911, 4, 181-223. 



8 Bussell, Soil Conditions and Plant Growth, 1915, p. 54. 



31—2 



