Coal Breccias are rocks that are composed of a mixture of coal fragments with a parent matrix material. They can be formed in a number of ways, most of which involve a coal bed being disrupted by some kind of geologic disturbance, and the resulting pieces being mixed with other materials and then deposited as a sedimentary layer. Examples of these disruptive events include mudslides, avalanches, tsunamis, and earthquakes. The distance that the coal fragments have traveled from their original location can sometimes be inferred by their density, as well as by their size and shape — the smaller the pieces of coal breccia and the more rounded their edges, the further they have traveled.