The structure of the Ordovician succession in the Ringerike district is described. Two zones of differing structural styles are recognised to the north and south of a major structure, here named the Klekken Fault. The middle and upper Ordovician strata in the south are gently folded but in the north the lower
Ordovician rocks dip steeply northwards and are repeated many times by high-angle strike faults. These structures are related to a thrust system which was emplaced over the younger, lesser deformed, rocks to the south. The regional implications of this structure are outlined.