Rather, gravel is a way to classify crushed rock that has naturally eroded over time based on the size of its fragments. You can have gravel that is made of granite, limestone, sandstone ...

Even the balmy tropics may have once been crushed by colossal masses of ice ... The telltale rocks are called Tava sandstone, which are exposed in the Rocky Mountains. As you might have guessed ...

The floor of the gully sloped steeply south, conforming to the slope of the hillside, and was littered with sandstone boulders and crushed sandstone left behind as the slab moved downhill. Upslope ...