The accumulated materials resulting from weathering and awaiting transportation often cover to some depth the parent rocks from which they have been derived. These accumulations of disintegrated and decomposed rock fragments are referred to as the regolith. The thickness of the regolith depends upon the relative rates of its formation by weathering and its removal by the gradtional agents. On steep slopes where gravity or rain wash removes rock fragments about as fast as they are loosened, or in dry or cold areas where weathering is very slow, the regolith may be thin or patchy, permitting the bare and solid rock to be seen. These exposures are referred to as outcrops (Trewartha et al. 229).