‘Pressure shadow’ type structures, referred to here as ‘mica beards’ (Ransom, 1965), are described from a sequence of deformed Ordovician greywackes. The beards are very numerous and constitute a major fabric element in definition of an axial‐plane foliation. They consist of fine, polygonal grains of quartz and of layer silicates which are aligned approximately perpendicular to the surface of the host grain with which they are associated. Three possible explanations are offered for the formation of the structures and their relative merits are discussed briefly.