Predominantly reddish-brown, but also beige, grey or variegated, silty to very fine-grained sandy mudstones. Intercalated sandstone beds consist of sheets of 2 to 30 m thick. The sands are light, greenish to yellowish, grey or red, subangular to rounded, moderately- to well-sorted, fine- to coarse-grained. The mudstone intervals are between 10 and 70 m thick, averaging around 40 m. Carbonaceous particles are common in grey mudstone intervals, especially in the lower part. Coal seams are very rare to absent.
Predominantly well-drained, distal fluvial-plain or flood-plain setting, with sheet floods and minor channelised fluvial systems.
Placed at the base of the first mudstone interval which is more than 60 m thick, overlying the uppermost massive sandstone bed of the Hellevoetsluis Formation. Where sediments are too fine-grained to be called Hellevoetsluis Formation, the Strijen Formation can (more or less conformably) rest on the Maurits Formation.
Truncated by the Saalian Unconformity. Formerly, the Carboniferous in most of the Campine Basin has been thought to be overlain directly by the Lower Germanic Trias Group.