Water also is a powerful erroding force. Water is capable of lifting great weights and rubbing off layers of rock. The force of the water helps chip away the rock and floating pieces act as miniature hammers to break even more pieces off. Again, the harder the layer, the slower the process. So we get areas like the grand canyon where the river has always traveled the path of least resistance and broken down the weaker rocks first.
Some rocks are harder than others.
However nothing I personally can do will break apart granite unless I get help from a hammer or other device. This varying hardness means that wind and other forces such as water, wear through some kinds of rock faster than others. Granite is an igneous rock that cools deep inside a volcano rather that erupting out. Sand then may be carried off by rivers, glaciers, or winds. Relate Activity and Concept Students can take turns examining the large grains with the magnifying glass.