S.E.M. studies of the clastic components of calcareous concretions from the late-Devensian, glaciomarine Errol Beds near the type site, east-central Scotland, reveal fabrics indicative of deposition from originally flocculated suspensions. Previously undescribed spherical cavities 30–350 µm in diameter, characteristically fringed by aligned platy particles, are thought to have been former gas bubbles around which the grains adhered by surface tension. It is suggested that the gas was ammonia, believed to have been derived from the decay of proteinaceous organic matter which promoted localised CaCO3 precipitation through a rise in pH. The delicate, porous fabrics preserved via cementation indicate that the concretions are of early diagenetic origin and formed rapidly, close to the sediment–water interface. In contrast, the fabrics shown by the host clays are consistent with consolidation of originally flocculated materials.