484 Transactions. 



D. Soils of the Oxford Clay. 



1. Colour: Shade darker than Gault. 



2. Texture : " The soils are not quite so sticky as those of a typical Gault, 



but in all other respects they are much the same " ; " bare fallow 

 is necessary." 



3. Crops : Clover, beans, wheat, barley, oats — fair crops in good seasons ; 



basic slag a profitable manure. 



4. Weeds: Abundant — (14), (3), (2), (5), (7), (16), Anthemis Cotula, 



Sherardia arvensis. 



Discussion : This summary makes it perfectly clear that all these clay 

 soils resemble one another closely so far as their agricultural properties 

 are concerned. Their textures are the same, their crops, and their weeds. 

 Bearing in mind, therefore, the purposes of a soil survey it would be much 

 more useful to group them all together in one series. Thus we arrive at 

 the following conclusions : — ■ 



1. The generalization that each geological formation produces a unique 

 soil type is not justified. 



2. On the contrary, clays from all formations resemble one another as 

 closely as possible in all essential agricultural characteristics— namely, in 

 texture, in cropping-capacity, and in methods of farming ; and the same 

 remarks apply to loams. 



3. The rigid application of the geologico-chemico-petrographical method 

 of classification used in recent British work leads only to a needless 

 multiplication of soil series and formations. (Bigg finds seven series in 

 the Biggleswade district, subdivided into fourteen formations.) 



4. In exceptional cases a geological formation may consistently give rise 

 to a unique type of soil — for example, it appears that soils on the green- 

 sand always have an exceptionally high percentage of coarse sand. 



Beturning now to Tulaikoff's summary of scientific classifications (p. 476), 

 there still remain — (3) the physical, according to the mechanical composi- 

 tion and the physical characteristics derived from it ; and (4) the com- 

 bined classification, by which soils are divided into groups — for example, 

 according to mechanical composition — and subdivided according to either 

 their chemical composition or other features. The fourth method em- 

 bodies the principle of the third, and we may conveniently discuss them 

 together. 



It will be seen at once that mechanical composition, on which soil- 

 fertility so much depends, is given due prominence ; while that misleading 

 feature, chemical composition, is properly suppressed. This is the method 

 of classification adopted by the United States Bureau of Soils. With them 

 the series is the central term. A series is a group of soils having a common 

 origin, and agreeing in such physical characteristics as colour, and differing 

 only in texture. The units of which the series is composed are called 

 " types." Thus the Miami series includes the Miami gravelly loam, the 

 Miami fine sand, the Miami silt loam, &c. Altogether there had been 

 recognized, in 1909, 715 different types of soil, classified into eighty-six 

 series, which again are grouped into thirteen great soil provinces. The 

 broader grouping into soil provinces " depends upon certain similarities 

 in the soil, due in part to the character of the original material and in part 

 to dominant agencies operating in the formation of the soils," such as 

 climate, heat metamorphism, oceans, rivers, volcanoes, topography. 



