IO2 SOILS. 



bauxite, disapore, 1 or in the gelatinous state, the nature of the 

 soils containing it proves that it is totally destitute of plasticity 

 and adhesiveness; and this consideration will often serve to 

 explain the fact that soils showing in their chemical analysis 

 high percentages of alumina, nevertheless show quite low de- 

 grees of plasticity, adhesiveness and water absorption. What 

 part it may take in modifying the physical properties of the 

 soil we can thus far only conjecture. 



Influence of the granular sediments upon the tilling qualities 

 of Soils. Considering the granular sediments by themselves, 

 in the absence of clay, it may be stated in a general way that 

 while in a moist condition they flocculate sufficiently to pro- 

 duce a fair tilth, they will nevertheless on drying collapse into 

 a close arrangement resulting from the single-grain structure. 

 The form of the grains being angular instead of rounded, they 

 are apt to form a very closely packed mass far from suitable 

 to vegetable growth ; as will be seen by an example taken 

 from one of the culture stations of the University of California, 

 from a piece of land which on the surface would be called a 

 very sandy loam, but after we descend increases in its content 

 of fine grains until at a depth varying from eighteen inches to 

 three feet we find w 7 hat appears to be a hardpan, which is 

 equally impervious to roots and water and causes the water to 

 stagnate to such an extent that after heavy rains the land 

 becomes so boggy as to render plowing almost impossible with- 

 out endangering the team. A close examination of this hard- 

 pan shows that, unlike others; it is devoid of any cement, and 

 when taken out can be readily crushed between the fingers, and 

 softens in water, but does not become plastic. Its impervious- 

 ness is therefore due solely to the close packing of the sand 

 grains, for it contains practically no plastic clay, and under 

 the microscope the grains are seen to be angular-wedge-shaped 

 and composed of the remnants of granite. The physical 

 analysis shows the following result : 



1 Bauxite is not only the most abundant of the three hydrates of alumina 

 known to occur naturally, but also stands nearly midway between the two others 

 in its water content, viz., a little over 25 ; that of diaspore being nearly 15^ 

 gibbsite about 35 . 



