Weathering and Erosion
Lots of people don't know the difference between weathering and Erosion but Geologist do. When some thing is weathered it is broken down into smaller pieces but when something is Eroded it is moves away. Chemicals in rain can cause it to weather the Statue of Liberty and turn her green. If that rain water is in a river then it can cause erosion by moving rocks down stream.
Try some chemical weathering on Chalk in this experiment.