A study of the exchangeable bases of some East Anglian soils derived from the Jurassic and Cretaceous sediments, with special reference to their marine origin

Abstract

Summary1. The results are recorded of an investigation of the exchangeable bases of some East Anglian soils derived from the Oxford, Ampthill, Kimeridge and Gault formations of the Jurassic and Cretaceous ages.2. As they were formed under the sea the original sediments contained sodium-clays but on the return of terrestrial and fresh-water conditions the character of the deposits was completely changed and they now contain only traces of exchangeable sodium.3. In the unweathered clay, represented by the 2 ft. below the top 18 in., exchangeable calcium forms only 75 per cent. of the total, and magnesium 20 per cent. As a result of leaching and weathering the magnesium on the surface is replaced by calcium which in the top 18 in. forms 85 per cent., while the magnesium is only 10 per cent. Thus the surface and deeper soils are distinguished by characteristic calcium: magnesium ratios.