30 



Soils 



from place to place but are deep and uniform. The physical make-up of all 

 these soils is pecuhar, and unlike anything commonly encountered else- 

 where. Coarse sand particles are generally absent, but fme sand is present 

 in quantity, especially in the lighter silts. The silt fraction is more pro- 

 minent in the heavier sUts. The Shell Marl soils, derived from material 

 formed in the clear vv^ater of shallow meres, occur farther south as patches 

 among the true black peats. They are white or grey in colour, highly 

 calcareous, with numerous small freshwater shells or shell fragments 

 present. The chief shell marl areas are on the sites of Stretham Mere and 

 Soham Mere. Skirt soils, from their location and constitution, appear to 

 be the result of conditions where both the accumulation of peat and the 

 deposition of silt or drift have alternately held sway. They might be 

 described as mineral soils with a rather liigher content of organic matter 

 than usual and a darker or black colour. 



Representative data of these typical soils are summarised in the following 

 table : 



CONSTITUTION OF MAIN TYPES OF TOP SOILS 



The figures show the percentages of carbonates and of each of the four usual 

 mineral-particle size-groups in the air-dry soil after passing through a 2 mm. sieve 



