Clay Colloids as a Cause of Bedding in Sedimentary Rocks

Colloidal clay of the montmorillonite-beidellite group extracted from the Putnam soil of Missouri was studied under the petrographic microscope while undergoing flocculation. The floccules were relatively coarse aggregates so well oriented as to resemble crystals. They were platy in shape, resembling in that respect the mineral in a bedded clay shale. It is suggested that bedding in shale may originate in part in the colloids contributed to it, that clay may be carried far seaward as a colloid and be flocculated and deposited in coarser floccules, and that clay partings and films in limestone may originate from flocculated clay colloids. The texture of fire clays is contrasted with that of shale.