lOO 



SOIL CONDITIONS AND PLANT GROWTH 



either left in situ or transported only a short distance, such as 

 the soils investigated mineralogically by Lagatu (82) in France, 

 those studied chemically by Hendrick and Ogg (132) in Scot- 

 land, and by Robinson (240) in N. Wales, and various glacial 

 and loessial soils of the United States. The case of extreme 

 change is shown in the secondary and tertiary soils of the 

 south-eastern part of England and in the soils of the Atlantic 

 coastal plains of the United States. 



These grades are illustrated by the following summary by 

 McCaughey and William (186) of the minerals present in the 

 sand and silt fractions separated from various United States 

 soils : — 



The clay fraction cannot be dealt with by mineralogical 

 methods : this indeed is their weakness, they break down for 

 the finest particles where they would be most helpful.^ 



Failyer, Smith, and Wade (97) have made numerous chemi- 

 cal analyses which also show the successive eliminations of 

 minerals other than quartz in these grades of soil : — 



^ An improvement in technique has been effected by Victor M. Moss^ri 

 (hes depots Nilotiques des Gazayer et Saouahel d'Egypte. Bull, de VInst. d'Egyptey 

 1919, I, 151-180). 



