Hard ground in the coraliferous Kimmeridgian depos its of the Holy Cross Mts., Central Poland

Presence of a hard ground was stated in the top of the coraliferous layer in the Lower Kimmeridgian of the Holy Cross Mts. Its origin is due to a gap in deposition, which was caused in turn by the filling up of the basin almost to the water mark by growth of coral bunches and by associated sediments. During the gap the corrosion processes started both of the sea floor and of coral skeletons in places where the tops of coral branches contacted with the sea floor. This corrosion was caused by pH changes, which are characteristic of shoals, and took place mainly after rainfall. The influence of coral bunches on the sedimentation and the deposition of associated sediments is also discussed