A large and gentle sloping land is often developed in and around the piedmont lowland or the remnant erosion surface. A large-scale landslide is sometimes found on this sloping land. This kind of landslide is generally regarded as the secondary sliding of the gentle inclined plane formed by the original landslide. In our country, however, boulders or block streams produced by earthquakes or volcanic activity or the climatic change have buried valleys in the mountainside to form the gentle slopes. Therefore, when rock is apt to slide by nature, a varied phenomenon takes place at the boundaries between the layer of gravel filling buried valleys and the rock, and new landslides often occur near these buried valleys. Since the buried valleys are usually stabilized, attention should be drawn to the soft rock surrounding them. Hence, the secondary sliding of the large sliding area formed in the past should be investigated over again for the landslide occurring on some gentle sliding area.