1, where the river channel changes from narrow to wide. Because the density of gems is generally higher than that of river sand (it can be considered that the density of river sand is 2.5), the flow rate suddenly slows down, and the low-density ones will be washed away, while the high-density ones will remain. The gem particles are large, but after deposition, they roll and sink in the upstream direction due to scouring.

2. Where the river turns. Due to centrifugation, it will be thrown out of the solitary shape.

3. Where the river forks. After the river bifurcates, due to the decrease of velocity, triangular sediment deposition is formed at the bifurcation. Dig upstream at this position.

The river was cut off to form a waterfall. Because the impact will form a pool, the outermost sector is distributed in the downstream direction of the pool. The main reason is that the tan water pushes outward in waves. After the coarse sand is dug, the stone is cleaned by gravity beneficiation.