Apparent and True Dip

Cross-bedded building stone. The contact immediately below A appears to dip gently to the right, but at B, the contact appears to dip to the left. But it's not a syncline! Both of those views are oblique, rather than perpendicular, to strike, so they only give the apparent dip. Because strike is roughly parallel to the plane of the photograph, the true dip of the bed comes directly out of the screen.

Hugh Hurlow emptying water bottle in desert.

As true dip is the steepest path down a planar surface, water will flow directly down true dip--marked here by the red arrow (you can also see where the water is because it's darkened the light-colored dolomite). Notice that these foliation surfaces appear to dip gently to the left in the upper right corner of the photo and appear to take a sudden turn just below the geologist's left leg, as if they were folded. But the surfaces are not folded; they are planar. The sudden turn is just the way they appear when viewed from different angles. Incidentally, the geologist who sacrificed his water to illustrate this phenomenon survived the ordeal.

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