The map of the limits of 25 metre thick coal shows it to be very extensive. Normally, mining goes down to about 300metres depth, but it may occasionally reach 400 metres. There are gentle dips. The faults post-date the coal, but may be contemporaneous with the overlying sands. In western Germany, the Tertiary is up to 800 metres thick.
Terrestrial sediments are to the southeast, and marine to the north.
There is evidence of marine transgression - causing interfingering. The largest faults are about 600 metres throw. Most are much smaller than this, creating a stepped structure. The area is regarded as one experiencing ongoing extension of the order of a few mm per year. Lithostratigraphical work has been undertaken, utilising the clays for correlation purposes.