Wild. — A Soil Survey of New Zealand. 477 



in which the soils are grouped according to the geologico-petrographical 

 character of the rocks which make up the soil (the classification of Fallow, 

 Mayer, and others) ; (2) the chemical or chemico-petrographical, according 

 to the main chemical features of the soil (Ki op) ; (3) the physical, accord- 

 ing to the mechanical composition and the physical characteristics derived 

 from it (Thaer, Schubler, the classification adopted by the Bureau of Soils 

 of the United States) ; (4) the combined classification, by which soils are 

 divided into groups, for example, according to their mechanical composi- 

 tion, and subdivided according to either their chemical composition or other 

 features (Senft, Kosticheff, and others) ; (5) the genetic, by which soils 

 are divided into groups depending on their origin and development (Pro- 

 fessor Docuchaiev, Professor Hilgard, Professor Eamman (in part), and 

 Professor Sibirtzev). 



The last-named, the genetic classification of Sibirtzev, provides a means 

 of differentiating in a broad way the soils of continental masses by means 

 of features that ultimately depend wholly on climate. Thus, while the 

 method provides a comprehensive classification in areas, such as Eurasia, 

 with more or less definite climatic zones, it cannot be applied to smaller 

 coimtries lying wholly within one climatic zone (such as England), nor 

 is it suited to a soil survey the objects of which are such as are outlined 

 in the second part of this paper. The method is well criticized by Hall 

 and Eussell,* and no apology is necessary for quoting at length their 

 remarks on the subject, since what applies to Great Britain in this connec- 

 tion applies equally well in New Zealand : " The genetic classification of 

 soils such as has been suggested by Sibirtzev divides soils into a series of 

 great types which are really determined by climatic zones. In the steppe 

 area, for example, where the black soils (Tchernozem) prevail, climatic 

 conditions have led to the accumulation of large proportions of mild or 

 neutral humus until it has become the dominant factor in determining 

 the character of the soil ; whether the original substratum be sand or 

 clay the amount of organic matter causes the soil to work lightly and yet 

 retain moisture. In such an area, and the area will in the nature of 

 things be large, soil analyses will be of little value because all differences, 

 chemical or physical, in the nature of the substratum will be overridden 

 by the preponderance of the humus. Such an area, again, will show little 

 relation between the soil and the geology of the country, the soil being 

 practically a drift deposit which has overgrown all the underlying forma- 

 tions alike. In the United Kingdom we must regard ourselves as living 

 almost entirely within one only of these large climatic zones, but one which 

 does not superimpose a soil type on all the. various strata to be foimd there, 

 so that a great diversity of soils may occur within a very small area. We 

 do see the climatic divisions in the peaty soils which develop in all parts 

 of the country above a certain elevation, for though some differences may 

 be traced in the vegetation carried by the moorlards, in the main the 

 character of the soils is alike and has been determined by the elevation 

 and the rainfall and not by the nature of the underlying formation. As 

 a rule, however, in the United Kingdom the soil is derived from and shares 

 the character of the rock or drift material below ; even where there might 

 have once been a common forest or steppe soil over a considerable area the 

 processes of cultivation carried on for so 'long have obliterated the excess 



* A. D. Hall and E. T. Russell, Soil Surveys and Soil Analyses, Journ. Ag. Sci., 

 vol. 4. 1911, p. 182. 



