X-ray analyses showed that illite and kaolinite are the dominant clay minerals of Kimeridgian (Jurassic) clays and that illite, chlorite, and kaolinite are present in Devonian clays traversed by borings in the London platform region (England). The Kimeridgian clays exhibit a certain relationship with Wealden (Cretaceous) clays of the region, but the latter contain greater abundances of mixed-layer material. No relationship is evident between the Devonian and the Wealden clays.

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