Definition: Gravel is an environmental material which is composed of pieces of rock that are at least two millimeters (2mm) in its largest dimension and no more than 75 millimeters.
Definition: A transition zone between different physiogeographic provinces that involves an elevation differential, often involving high cliffs. Most commonly a transition from one series of sedimentary rocks to another series of a different age and composition. In such cases, the escarpment usually represents the line of erosional loss of the newer rock over the older.
