Wild. — A Soil Survey of New Zealand. 485 



Any one studying Milton Whitney's bulletin* on the soils of the United 

 States with a view to getting clear ideas as to their criteria of differentiation 

 will be disappointed in the rather rambling, not to say ambiguous, way 

 in which the information is given. It is believed, however, that the fol- 

 lowing is an accurate summary of the more important of their criteria of 

 differentiation within the various divisions : — 



Soil province : Climate, and mode of formation (distinct from 



geological origin). 

 Soil series : Colourf ; mode of origin ; structure^ ) as distinct from 



texture ; nature of subsoil to depth of 3 ft. to 6 ft. 

 Soil type : Texture. 

 It will be observed that this scheme is less likely to create distinctions 

 where there is little or no difference, being based on those properties which 

 play the largest part in creating differences in the agricultural characters 

 of soils. 



The present writer proposes for this Dominion a method of soil-classi- 

 fication similar in principle to the above, but differing in the significance 

 of the terms " series " and " type " (formation) in ways that will presently 

 be explained. Arguments in its favour which are of general application 

 have been brought forward already ; and in the next section arguments 

 that apply more particularly to our special New Zealand conditions will 

 be submitted to the reader. 



II. Method of Soil Survey for New Zealand. 



It has been shown in the preceding section that the application of the 

 geologico-petrographical method of classification in England has resulted 

 in a multiplication of soil formations even within small areas, many of 

 these formations being exactly similar so far as concerns their agricultural 

 potentialities. As it has been proposed to apply this method to a soil 

 survey of New Zealand, it is necessary to add one or two arguments that, 

 in the writer's opinion, totally discount the applicability of this method 

 to the soils of this Dominion. 



In the first place, even assuming the success of the method in England, 

 we must draw attention to the very different conditions here. England 

 is a country roughly triangular in shape, of relatively low elevation, and 

 covered to a considerable extent with soils formed in situ. New Zealand 

 is a long and narrow country ranging through a thousand miles in latitude, 

 dominated by a mountain axis of great altitude, and bordered on either 

 flank by plains formed from the material carried down from these moun- 

 tains by rivers and streams. These plains comprise a great portion of 

 the agricultural land of the country. Many of them in both Islands are 

 formed from the detritus of the main axis, which, throughout a great part 

 of its length, is of tolerably uniform geological structure. The plains so 

 formed should therefore, in a geologico-petrographical classification, be put 

 into the same soil group. 



But it has already been shown that the features chiefly responsible 

 for the productivity of a soil are, in order of their relative importance,^ 

 (1) climate, internal and external ; (2) texture ; (3) composition ; (4) nature 



* U.S. Dept. of Agric, Bureau of Soils, Bull. No. 55. 



t Colour is considered an important indicator of soil- fertility conditions by the 

 United States Soil Survey, though why this is so is not apparent. 



J These factors cannot be arranged in a rigid order of importance, as they react 

 on one another. 



