Water At Work

One of the most important factors in considering their evolution has to do with the natural cracks or joint sets in the rock. You can see these parallel joint sets as rounded vertical and horizontal breaks where one rock mass appears to lean against another. While still buried in the Earth, groundwater percolated into the joints where it slowly decomposed minerals in the rock along cracks. Some areas with closely spaced joints were completely reduced to sand, while large rounded rock formations were left in areas with widely spread joints.