Wild. — A Soil Survey of New Zealand. 479 



In the first place, if what has been said above be borne in mind — ■ 

 namely, (a) that the objects of a soil survey are not merely to provide a 

 scientific classification of soils, but to provide such a classification as will 

 enable us the more readily to appreciate the agricultural potentialities of 

 each soil type ; and (b) that the fertility of a soil depends not so much 

 on its chemical composition as on its texture, its climate, and the environ- 

 ment generally that it provides for the plant — -then it must at once be 

 conceded that the geologico-petrographical classification is inefficient, since 

 it is based fundamentally on the nature of the rock from which the soil 

 is derived. For the character of the parent rock can affect only the 

 chemical composition (and in some few exceptional cases mechanical com- 

 position) of the soil, but it cannot affect climate, water-supply, texture, &c, 

 which are by far the most important fertility factors. 



Proceeding from this general statement to the consideration of specific 

 cases, we shall deal first with Rigg's paper mentioned above. Rigg 

 examined the following geological formations, and the series of soils occur- 

 ring on them were divided into soil formations which had different agri- 

 cultural properties : — 



(.1.) Oxford clay, giving rise to two soil formations — 

 (a.) Pure-clay soil ; 



(b.) A clay loam, probably resulting from an alluvial wash on to 

 the clay soil. 

 (2.) Greensand, giving rise to two soil formations — 

 (a.) Dark sands ; 

 (6.) Brown sands. 

 (3.) Gault, giving rise to two soil formations — 

 (a.) Pure-clay soil ; 



(b.) A sandy loam, locally known as " redland," occurring as a 

 narrow strip between greensand and the pure Gault clay 

 soil (a). 

 (4.) Boulder clay, giving rise to three soil formations — 

 (a.) Pure boulder-clay soil ; 



(b.) Heavy loam produced by wash on boulder clay ; 

 (c.) Sandy loam produced by a thin capping of boulder clay on 

 greensand. 

 (5.) Brick-earths, giving rise to only one soil formation. 

 (6.) Glacial, giving rise to one soil formation, which, however, is not 



quite so uniform as the brick-earth formation. 

 (7.) Valley gravels, giving rise to three soil formations — ■ 



(a.) A brown-soil formation (referred to as " Old Brown ") ; 

 (b.) A heavy brown-soil formation ; 



(c.) A more recent dark-soil formation (referred to as " New 

 Dark "). 



Samples of soil from each formation were collected and submitted to 

 chemical and mechanical analysis ; and by this means it is claimed that not 

 only were field observations verified, but analysis differentiated between 

 the various soil formations and showed an extraordinary uniformity between 

 the samples taken from any soil formation. The greensand soils are given 

 as an illustration of this. This series of soils is said to be " differentiated 

 from any other by the low percentage of potash and mineral salts and an 

 almost entire absence of calcium carbonate. The coarse-sand fraction is 

 particularly high, and this fact alone would be almost sufficient to dis- 

 tinguish it from any other series." When, however, we turn to the 



