Succession of green-grey, glauconitic, very fine-grained sand with, mainly in the upper part, a number of hard, calcareous sandstone layers of some decimetres thickness (leading to high-resistivity peaks). Towards the base of the unit the clay content increases, and the calcium carbonate content and amount of glauconite decreases. A minor amount of mica occurs. Farther from the palaeo-coastline the member becomes silty and marly. The upper part with the cemented, calcareous sandstone layers is very rich in fossil fragments, especially in the Achterhoek and Twente: abundant Nummulites, shells (including Pecten) and Echinodermata, indicating a near-shore environment.
Marine. Deposited in inner-neritic to near-shore environment. In general, the water depth appears to be shallowing upwards, with a possible exception for the uppermost part of the unit.
Variable in nature. Regionally it is an unambiguous boundary between the clay of the Ieper Member and the overlying sand. However, in many places the boundary is gradual and complex in nature, because different parts of the succession are missing locally as a result of several phases of erosion and/or non-deposition.
Contact with the overlying Asse Member is formed by the clear transition from sand to clay. Over large areas, the Brussels Sand Member has been eroded and is overlain by younger deposits.