Summary

Calculation of the true clay-mineral content of samples of Keuper Marl analysed has shown that much of the clay content has been aggregated into silt-size units. This aggregated structure accounts for the large range of measured Activities of the Marl.

A system of structural classification used in pedology will conveniently describe the structural features of the more heavily aggregated, overconsolidated clay soils such as Keuper Marl; some preliminary work with the electron micro-probe analyser supports this method of describing soil structure.

It is suggested that variations in the structure of these sediments indicate varying conditions of deposition and diagenesis, and are related to differences in the magnesium content of the samples analysed.