The pilot reported that he approached the airport, intending to land on the grass runway. He said that his approach was high and he introduced a slip in order to lose altitude. During the slip, the airplane turned to the left, which he did not notice. He continued the landing and the airplane nosed over. The airplane sustained substantial damage to the right wing and vertical stabilizer and rudder. The pilot stated that there were no mechanical problems with the airplane. Postaccident examination revealed that the airplane was landed in a marsh about 400 yards north of the east-west oriented runway.