minerals are dissolved in the water and carried along in solution. This typically occurs in areas where the underlying bedrock is limestone;
fine light material is carried along in the water;
small pebbles and stones are bounced along the river bed;
large boulders and rocks are rolled along the river bed.
The video below shows the movement of sediment in a river. Notice the different types of processes of transportation at work including traction (rolling of material over the river bed) saltation (bouncing movement) and suspension (material suspended in the water).