26 Soils 



slope. The ditches are often natural watercourses, and impermeability of 

 the formation is the only obstacle to its satisfactory drainage. 



PARENT MATERIALS AND SOIL-DRAINAGE CONDITIONS 



(i) With Free Drainage. (Parent material permeable, excess water 

 draining to depth) 

 A. Drainage Excessive. (Considerable leaching ; moisture-holding 

 capacity poor) 



limestones gravels and sands on chalk sands 



Upper Chalk Plateau Gravels Lower Greensand 



Middle Chalk Glacial Gravels Breckland 



Taele Gravels 



B. Drainage Free. (Moisture-holding power satisfactory for plant growth) 



LIMESTONES SANDS 



Lower Chalk Lower Greensand (Mid-Cambs) 



Coral Rag 



(2) With Impeded Drainage. (Subject to continuous or seasonal 

 water-logging) 

 A. Drainage Imperfect. (Subsoil and parent material impermeable) 



CLAYS 



Boulder Clay 

 Gault AmpthiU Clay 



Kimeridge Clay Oxford Clay 



B. Drainage Impeded. (High water table due to topography; underlying 

 stratum impermeable, or low permeability) 



LIMESTONES GRAVELS ALLUVIUM 



Chalk Marl Valley Gravels Peat 



Lower Chalk (base) Old River Gravels Silt 



Middle Chalk (base) 



Most of the soils reflect to a marked degree the characteristics of their 

 parent materials or the geological outcrop on w^hich they lie, but this is 

 not invariably the case. Textures vary from the loose sands of Breckland 

 to the heaviest Gault, Boulder Clay or Oxford Clay soils. In general, the 

 lime status of the soils is satisfactory or good, the only serious exception 

 being the soils derived from the Lower Greensand (especially those in the 

 west of the County), and some of the Gravels. This is to be expected of 

 soils formed from cretaceous rocks, or drifts originating in the neighbour- 

 hood of cretaceous exposures, or associated with rivers of calcareous waters. 



Boulder Clay soils occupy two substantial areas, one in the south-east 

 along the Essex border, and one in western Cambridgeshire on the 

 Htmtingdonshire border. They are buff-coloured clays or clay loams. 



