Structural analysis of a valleyward tilting structure of slate in the Setogawa Group of the Simanto Belt indicates that it is a bending fold produced by fracturing and slipping along slaty cleavages, which is caused by gravity. Formation process of the tilting structure is explained as follows:
(1) At the initial stage, well-persistent cleavage plane fractures grew along slaty cleavages.
(2) At the next stage, the rock masses separated by the well-persistent cleavage plane fractures bended individually with growth of many short cleavage plane fractures.
(3) At the third stage, fracturing of tension fracture perpendicular to cleavages, wedge-patterned fracture zone and fold-shaped pattern of short cleavege plane fractures were developed in a zone and resulted in the formation of a hinge of bending fold. The producing fold is asymmetric.
(4) Finally, the movement type of the folded slate changed by gradation from creep to topple.
