Suture is a kind of pressure-soluble structure. A fracture structure common in carbonate rocks. The cause of this is controversial, but most believe that dissolution is mainly caused by the pressure and temperature of the overlying formation. The profile is a zigzag curve; the plane is a jagged and uneven surface; the three-dimensional is a cylinder with concave and convex sizes. The size differs greatly, and some of the uneven fluctuations are very obvious, while others are flatter and even gradually disappear with the level.