THE MINERAL CONSTITUENTS OF THE) SOIL SOLUTION 33 



and the alternating formation of rock and soil from the same 

 materials is probably an agency, in some part at least, in the 

 mixing of soil material. The action of water in carrying off 

 and transporting surface material and in gullying and eroding 

 sloping surfaces is probably a large factor. But this agency, 

 like the first, is rather restricted and localized. Just as important 

 as a mixing agency is the wind. This, unlike water, works up- 

 hill as well as down, and is more or less in action at all times, 

 continually transporting soil material from place to place. Wind- 

 borne dust on roofs of dwellings, on rocky mountain tops and 

 similar places, where it could have been brought by no other 

 agency than the wind, is sometimes found supporting vegetation. 

 Many chemical and mineralogical analyses of wind-borne dust 

 obtained from various locations show it to have generally the 

 same essential characteristics as ordinary soils. 



Aside from the quartz and ferruginous materials mentioned 

 above, the major part of the soil minerals are silicates, ferro- 

 silicates, alumino-silicates or ferro-alumino-silicates, of the com- 

 mon bases, sodium, potassium, calcium, magnesium, and ferrous 

 iron. Other bases, such as lithium, barium, or the heavy metals 

 may occasionally be present in appreciable amounts as may 

 other types of silicates, or other mineral salts, but these may be 

 regarded as more or less incidental and rarely affecting in any 

 essential way the general character of the soil mass. These 

 silicates or silico minerals are all somewhat soluble in water, 

 and being salts of weak acids with strong bases, are greatly 

 hydrolyzed. A convenient illustration is afforded by the well- 

 known rock and soil mineral, orthoclase. Assuming its type 

 formula, the reaction with water may be represented. 

 K.AlSi 3 O 8 + HOH 5 H.AlSi 3 O 8 + KOH. 



Under ordinary soil conditions, with a relatively large propor- 

 tion of carbon dioxide in the soil atmosphere, the potash formed 

 would be more or less completely transformed to the bicarbonate, 



KOH -f CO 2 + H 2 O * KHCO 3 + H 2 O. 



Confirmation of this view is afforded by the natural associations 

 and known alteration products of orthoclase. 



