Dip

In the context of geology, stratigraphic dip is defined as the maximum angle from the horizontal in the plane of a stratigraphic unit. The direction in which the dip should be measured is known as the dip-direction. If the surface of the unit is not accessible (for instance, only a cross-section of the unit is visible, as in a cliff-face), only the apparent dip can be measured.

In the field, the dip-direction is commonly identified using either a clinometer, or by pouring water on the surface of the rock(if it is accessible) and observing the direction of flow. For any inclined surface, there will also be two directions of zero-dip. The direction that is anti-clockwise of the dip-direction is known as the strike.