Soils 27 



lying on clay subsoils, containing from i to 10 per cent calcium carbonate, 

 much of it as rounded chalk pebbles. The depth to the grey Chalky Boulder 

 Clay varies considerably. In some places, it can be reached within 2 ft. of 

 the surface, but, on the lower slopes and in the smaller valley bottoms, 

 there is often almost this depth of coUuvial heavy loam material before a 

 buff clay subsoil is reached, and this in its turn gives place to grey un- 

 weathered clay. The drainage of these soils is naturally poor, although the 

 two areas are in the highest parts of the County. The western area is the 

 most impermeable. On high ground, where land is flat or only gently 

 sloping, run-off is hindered, and water-logging or surface pools are of 

 common occurrence in a wet winter. Smaller areas of Boulder Clay soils 

 are also found in the "islands" of the Fens. 



The Upper Chalk formation in Cambridgeshire is covered, for the most 

 part, by Boulder Clay. The soils on the hmited exposed areas vary from 

 thin white or grey chalky soils to brownish grey loams, depending on the 

 proximity of the Boulder Clay and the extent of downwash from it. 



The exposure of the Middle Chalk occupies a big proportion of Cam- 

 bridgeshire, and is covered by two main classes of soil. One is a thin grey 

 or brownish grey chalky loam, consisting mostly of fragments of chalk, 

 and lying directly on raw chalk. This chalky, or "whiteland", type 

 occupies the higher slopes and summits especially along the flanks of the 

 exposure. The other is a warm brown or reddish brown loamy sand, up 

 to 20 in. deep, lying on the chalk. This "redland" type consists chiefly of 

 coarse sand with only a small percentage of calcium carbonate. It fills the 

 lower slopes and flatter areas, especially around the numerous patches of 

 Gravel scattered along the outcrop. The soils on these Gravels are dis- 

 similar only in respect of their greater content of flint pebbles. All the 

 soils on the Middle Chalk are, with the exception of hollows and limited 

 areas on the north-west edge of the outcrop, characterised by very free 

 drainage. This constitutes their chief drawback, and the farmer's great 

 difficulty is to conserve sufficient moisture in the soil to carry the crops 

 through the growing season. 



The Lower Chalk soils differ from those of the Middle Chalk, chiefly 

 in that they are less deep but heavier in texture and have a narrower 

 range of colour. They are free draining but the water table, in general, 

 comes nearer the surface, and, in places, field drainage is necessary. Both 

 in the Lower Chalk soils and in a few of the low-lying parts of the Middle 

 Chalk, yellow motthng, the characteristic sign of impeded drainage, is to 

 be found in the subsoil chalk within 18 in. of the surface. 



The Chalk Marl soils occupy low-lying ground, much of it bordering 

 on the Fens. Both colour and texture vary as a result of surface admixture 



