1. Moenkopi Fm (Triassic), east of Las Vegas Classic oscillation ripples. Seen end-on, they are nearly symmetrical. Note the tuning-fork junction, common in such ripples. They act to adjust ripple spacing (as does a ripple coming to an end between the two adjacent ripples, not seen here).

2. Moenkopi Fm (Triassic), east of Las Vegas, Nevada Note that one ripple ends between the two adjacent ripples.

3. Ferron Ss Mbr, Manco Sh (Cretaceous), Utah Classic regular and symmetrical oscillation ripples.

4. Moenkopi Fm (Triassic), east of Las Vegas, Nevada This is a cast (a “negative”) of symmetrical oscillation ripples. It is unusual to see this: usually the overlying sedimentary rock is more weatherable than the bed that is topped by the ripples.

5. Off First Encounter Beach, Eastham, Massachusetts (Mass. Bay) These almost symmetrical ripples, on a broad offshore bar, were formed in water no more than about two meters deep.

6. Large oscillation ripples at long oscillation period (courtesy of John Lambie) These very large oscillation ripples were formed at a very long oscillation period. The high water temperature (61degrees C) gives a scale factor of about two, so multiply the length of the ruler by that factor.

7. Makran Coast, Pakistan. Scale bar = 0.5 m (courtesy of John Harms) Oscillation ripples this large are not common. The sediment is sufficiently coarse that there is no change to three-dimensional ripples with increasing flow strength.

8. (Scale bar in centimeters) “Ladder-back” ripples. The larger ripples probably formed before the secondary set

9. Ferron Ss Mbr, Mancos Sh, Utah How did these ripples form? I don’t know. Neither set seems dominant.

10. Bell Island Fm (Ordovician), near St Johns, Newfoundland It seems clear to me that these are oscillation ripples, but I have no idea how they formed. You can see a combination of hexagons, pentagons, and quadrilaterals, just in this small view.

11. Bedding plane, Johnnie Fm (Neoproterozoic), southern Nopah Range, California This bedding plane tops a garden-variety hummocky cross-stratified sandstone bed. It is roughly isotropic (no preferred dip directions). When viewed from a distance, it has an approximately hexagonal arrangement, with hummocks at the vertices and swales inside the hexagons. (Tragically, this bedding plane has since fallen apart.) Question: was the generating flow a bidirectional oscillation or a multidirectional oscillation? I don’t know.

12. Wood Canyon FM (Neoproterozoic–Cambrian), north of Las Vegas Looking straight down on a three-armed hummock on a hummocky–swaly bed top.