468 Studies of a Sn,ttisl, Drift S,,!1 



"fertile soils" while under (d) is f;iven the analysis from "less fertile 

 soils." 



Table VI shows: 



(1) That tlie percentage of silica is sinallcr in ;ill Iho fractions in 

 Craibstonc soil than in the corresponding fractions of the Knglish soils. 

 In the case of the three coarser fractions of English soil 91 per cent. 

 or over consists of silica. That is, these fractions almost entirely 

 consist of particles of more or le,ss finely powdered silica. Even in 

 the silt about 90 per cent, is sihca, and the coarser part of the fine silt 

 contains almost as great a percentage of silica as the fine gravel of 

 Craibstone soil. The granite of the Aberdeen neighbourhood in the 

 unweathered condition contains about 70 per cent, of silica and 18 

 per cent, of alumina. We may conclude, therefore, from the analyses 

 that the coarser fractions of Craibstone soil contain much unweathered 

 or partially weathered granitic material in addition to silica. This 

 conclusion w'as confirmed by the microscopic e.Kamination of these 

 coarser fractions and by comparison of them under the microscope 

 with similar fractions separated from powdered granite. The granite 

 used for these comparisons was obtained from a local quarry. 



(2) The coarser fractions of Craibstone soil are much riclier in 

 alumina than the corresponding fractions of the English soils. It is 

 only in the finest fractions, fine silt and clay, that the English soils 

 are at all comparable in respect of alumina with Craibstone soil. To 

 a certain extent the case of iron presents similar differences. 



(3) The coarser fractions of Craibstone soil are much richer in 

 potash and lime than the corresponding fractions of the English soils, 

 but the finer fractions are poorer. A similar richness in potash of 

 the coarse fractions was, as we have seen, noted by Robinson for soils 

 of N. Wales. Whereas in the English soils the finest fractions, fine silt 

 and clay, are the richest in potash and lime; in Craibstone soil the clay 

 is the jioorest of all the fractions in both potash and lime. 



While Crail)stone soil thus differs greatly from soils of the south- 

 east of England, there is a general similarity in type, so far as we have 

 data for comparison, between it and the American soils which have 

 been produced by mechanical pulverisation rather than by profound 

 chemical weathering. Thus Craibstone soil is much nearer in type 

 to the Glacial or Residual soils of Table V than to the Coastal i'lain 

 soils. On the other hand the South of England soils conform more 

 nearly in type to those of the Coastal Plain than to the Glacial or 

 Residual soils. 



