The structure here named eolian microridges consists of a series of anastomosing ridges less than 1 cm. in wave length. Eolian microridges have been observed to form where sand was being blown in saltation across wet sand surfaces, mostly on beaches. The ridges and intervening troughs are oriented transversely to wind direction and commonly have several types of asymmetry by which the direction of the wind that formed them can be determined. The structure may be distinguished from ordinary ripples of unusually small wave length by several criteria other than wave length. Eolian microridges are potentially preservable, and structures found on several bedding planes of the Keefer Sandstone (Middle Silurian) near Lewistown, Pa., are possibly preserved examples. These structures, together with other evidence, strongly suggest a beach environment for this sandstone.