J. Hendrick and W. G. Ogg 4G5 



Failyer, Smith and Wade^, of the U.S. Bureau of Soils, studied the 

 separates of a large number of soils of the United States, and in their 

 report on " The Mineral Composition of Soil Particles" they give a useful 

 resume of the whole subject. In their mechanical analyses they divided 

 their samples into three grades only, namely, sand (2--05 ram.), silt 

 (•05— 00.5 mra.), and clay (-005-0 mm.). Phosphoric acid, potash, lime, 

 and magnesia were determined in these fractions by fusion methods. 



One of the groups of soils thus examined came from the Coastal 

 Plains '' which are made up of unconsolidated gravels, sands, silts and 

 clays, derived in most part from the erosion of the Piedmont Plateau 

 and other inland areas. These materials were mainly deposited on the 

 then ocean floor and have been brought to their present level by the 

 elevation of the land areas.... While the soils of this region present 

 many diversities among themselves, due to special circumstances 

 affecting their deposition or subsequent history, they all differ much 

 from the parent rock and have been subjected to excessive weathering 

 and leaching." Seven soils of this group were examined. 



A second group consisted of residual soils from crystalline and 

 metamorphic rocks. " The method of formation, in addition to 

 pulverisation, has been one of removal of certain parts of the rocks, 

 either by solution or mechanically by moving water or air, leaving 

 the present soil as a residue. The material forming the soil may difier 

 but little chemically and mineralogically from the rocks whose breaking 

 down has produced the soil, or it may depart much from them." Only 

 three soils of this group were examined. 



A third class examined consisted of soils of glacial origin. This 

 group "includes soils formed from material deposited by glaciers or 

 this material somewhat reworked by water, and also loessial soils, 

 consisting largely of particles the size of silt, which have been 

 carried from other glacial areas and deposited over the underlying 

 material.... The glacial soils consist largely of crushed rocks. Much of 

 the material composing them has not been profoundly weathered. 

 They are therefore quite similar in composition to the residual soils, 

 and hence differ from those of the Coastal Plains." Ten soils of this 

 class were examined. 



The soils of each class examined by Failyer, Smith and Wade 

 differ considerably from each other, but show certain general simi- 

 larities among those of the same class. Each class exhibits distinct 

 differences from the other classes. In particular the soils of the Coastal 



' U.S. Bureau of Soils Bnll. 64, 1908. The Mineral Composition o£ Soil Particles. 



Journ. of Acrric. Sci. Vil ' 31 



