Blatter and others think that the factors to control erosion are: ① erosion can't happen before running water has the ability to erode sediments; (2) Local erosion must be balanced by sediments in any other place; (3) When the local water surface rises due to erosion, the scouring rate decreases; ④ Sediment movement caused by erosion often leads to the accumulation of the coarsest components as residues, so that the residues can protect the surface and prevent further erosion.

When the water flow is strong, the eroded sediment will deposit downstream, or spread to the downstream and lateral low-speed and low-turbulence areas, forming local accumulation.

The scouring of viscous sediment (mud) can deposit downstream to become endogenetic conglomerate (Figure 2- 1 1). Many imprints formed on the mud surface are usually preserved as imprints on the bottom of sandstone strata, which are formed by the erosion of newly deposited mud, such as scouring or gully marks.