Weathering

Weathering is the process of change, especially decomposition, of |rocks and other sediments due to chemical changes. When the changes are also due to mechanical processes, it's called erosion. 

Chemical weathering of rock and sediment minerals and the leaching out (loss) of the more soluble parts produces soils. 

The first-stage formation of caves, when limestone joints are enlarged due to the solution of the calcium carbonate, by the inorganic and humic acids in the water, is a kind of weathering. The sub-surface breakdown of rock on hillsides is also a common mode of weathering. Where rock is especially resistant to subsoil weathering, rock outcrops occur, but more often the rock decomposition is taking place unseen due to chemical forces.