The soil clays of Great Britain: I. England and Wales

Abstract The mineralogy of the clay fractions (<2 µ m) of the major soils of England and Wales is reviewed, and the data presented in terms of the 1:250 000 National Soil Map. Most soils developed in pre-Rhaetic sediments are dominated by mica with lesser amounts of chlorite and kaolin. Exceptions are soils developed in calcareous Coal Measure shales which have significant smectite contents, and freely drained soils in Keuper Marl which contain swelling chlorite, sepiolite and palygorskite. Soils developed in post-Triassic sediments are dominated generally by expansible minerals, except for those developed in Lower Lias and Estuarine Series rocks (Jurassic) which are dominated by mica and kaolin respectively. The presence of loess in soils seems to be associated with the occurrence of a complex interstratified mineral with X-ray diffraction properties akin to vermiculite. Weathering of soil clays is most marked in the wetter uplands, but over most of lowland England is detectable only by slight changes in non-exchangeable potassium content and cation-exchange capacity towards the soil surface. Applications of soil clay mineralogy in the fields of plant nutrition and soil mechanics are discussed, in particular the production of maps showing mineralogical provinces.