What is "dip of a stratum"

Dip \Dip\, n.

1. The action of dipping or plunging for a moment into a liquid. ``The dip of oars in unison.''
   --Glover.

2. Inclination downward; direction below a horizontal line; slope; pitch.

3. a hollow or depression in a surface, especially in the ground.

4. A liquid, as a sauce or gravy, served at table with a ladle or spoon. [Local, U.S.]
   --Bartlett.

5. A dipped candle. [Colloq.]
   --Marryat.

6. A gymnastic exercise on the parallel bars in which the performer, resting on his hands, lets his arms bend and his body sink until his chin is level with the bars, and then raises himself by straightening his arms.

7. In the turpentine industry, the viscid exudation, which is dipped out from incisions in the trees; as, virgin dip (the runnings of the first year), yellow dip (the runnings of subsequent years).

8. (A["e]ronautics) A sudden drop followed by a climb, usually to avoid obstacles or as the result of getting into an airhole.

9. a liquid, in which objects are soaked by dipping; e.g., a parasiticide or insecticide solution into which animals are dipped (see sheep-dip).

10. a sauce into which foods are dipped to enhance the flavor; e. g., an onion dip made from sour cream and dried onions, into which potato chips are dipped.

11. a pickpocket. [slang]

    Dip of the horizon (Astron.), the angular depression of the seen or visible horizon below the true or natural horizon; the angle at the eye of an observer between a horizontal line and a tangent drawn from the eye to the surface of the ocean.

    Dip of the needle, or Magnetic dip, the angle formed, in a vertical plane, by a freely suspended magnetic needle, or the line of magnetic force, with a horizontal line; -- called also inclination.

    Dip of a stratum (Geol.), its greatest angle of inclination to the horizon, or that of a line perpendicular to its direction or strike; -- called also the pitch.