Miniature graben

“Graben” means grave, and we see on the surface of this little piece a long, narrow depression resembling, if we use our imagination, a dug grave. The end view, in cross section, reveals that the depression is due to normal faults, dipping inward toward one another, and accommodating movement of hanging wall down. The uppermost white quartz layer (thickest) is seen in the footwall on each side, and in the graben proper, such that it is possible to measure offset. “Graben” is usually reserved for large regional structures, such as the famous Rhine Graben in Germany, but here we have a pocket graben.

I was skipping stones along the beach, and when I picked up this stone I discovered its thumb-size depression, …and then geology took over play, though geology is play.  Like other geologists, I am fascinated when I see “miniatures” of tectonic features that normally make up large regions of mountain belts.