Balk Member

Grey clay, sandy, mostly non-calcareous, devoid of shells. Intercalated layers of fine to medium sand, non-calcareous and devoid of shells. Light grey very fine to fine sand, devoid of shells, fining westward.

Coastal plain (possibly delta top, including alluvial plain). Regionally, marine influence.

Sharp contact with glauconitic, commonly shelly, shallow-marine fine sand (Breda Formation). Gradual transition into or sharp contact with finer and more calcareous shallow-marine sand (Oosterhout and Maassluis Formations), or into non-calcareous, micaceous and brown fluvial sand and clay (Waalre Formation).

Gradual transition into fluvial sand (Peize Formation, undifferentiated).