THE SOILS OF THE CANE-GROWING REGIONS 65 



the basic rocks, which are mainly found in regions of comparatively recent 

 volcanic activity. The soils formed from the acidic rocks contain in general 

 more potash than do those of a basaltic origin, these being characterized 

 by the presence of larger quantities of iron and of lime. 



The following. figures, due to Burgess 2 as the mean result of the analysis 

 of 1547 American mainland soils, and of 515 analyses of Hawaiian soils, 

 illustrate the differences in composition between soils derived from acidic 

 and those from basic rocks. The analyses were made by official American 

 method, i.e., digestion in hydrochloric acid of sp. gr. 1-115 for 10 hours 

 at 100 C. 



MATERIAL. AMERICAN. HAWAIIAN. MATERIAL. AMERICAN. HAWAIIAN. 



Total silica .. 85-52 32-63 Manganese oxide 0-12 0*50 



Soluble silica 



Potash 



Soda 



Lime 



Magnesia 



6-40 17*59 Ferrous & ferric oxide 3- 81 28-02 



0*40 *34 Alumina.. .. 5**5 20-72 



0-27 0-35 Phosphoric acid o- 16 0-35 



"75 I *3 Sulphuric acid .. 0-04 0-32 



0-68 1-18 Nitrogen .. 0-18 0-33 



Classed according to physical condition, soil physicists recognise four 

 main types of soils : gravels, sands, loams and clays. To these are to be 

 added intermediate classes as sandy loams, clay loams ; etc. The distinction 

 which is based on the size of the soil particles is entirely arbitrary, and one 

 type passes insensibly into another. In the United States the distinction is 

 generally as indicated below other arbitrary and allied distinctions ob- 

 taining elsewhere : 



Gravel : Particles greater than 0*05 inch in diameter. 



Coarse sand : Particles with diameter lying between 0-05 and o- 02 inch diameter. 

 Medium sand : ,, ,, ,, ,, 0-02 ando-oi ,, 



Fine sand : ,, ,, ,, ,, ,, o-oi and 0-004 > 



Very fine sand : ,, ,, ,, ,, 0-004 and 0-002 



Silt: ,, ,, ,, - o 002 and 0*0002 ,, 



Clay: ,, ,, ,, less than 0*0002 inch diameter. 



A third method of classifying soils separates them into stationary and 

 transported soils. In the former class are those formed in situ as on plat- 

 eaus and on lands of small gradient, and as such their composition reflects 

 that of the underlying rocks from which they are formed. Transported 

 soils are either wind or water-borne, or else have been convej^ed by glacial 

 drift. When the motion is slow, as on the gentler slopes of a mountain 

 area, the term colluvial is applied ; such a motion usually takes place under 

 the influence of rainfall. When the soil is transported by a river, and finally 

 deposited in its overflow as a silt, the term alluvial is used, the glacial drift 

 formation receiving the term diluvial. 



To these types should be added the peat and bog soils that are formed in 

 situ, and to which the term cumulose is given ; other distinctions of less 

 importance are those differentiating between humid and arid soils, temperate 

 and tropical formations. 



It is at once apparent that all these distinctions overlap. A stationary 

 soil may be either basic or acidic, and an alluvial soil will partake of the 

 nature of the material over which has flowed the river to which its forma- 

 tion is due. This may be either basic or acidic, or a combination of both 

 types, and the nature of the soil will be influenced by the character of the 

 formation upon which the deposit is made. 



F 



