Modern asymmetric <a href="https://en.wikipedia.org/wiki/ripple_marks" class="extiw" title="w:ripple marks">ripples</a>. exposed in the intertidal zone near Lawrencetown, Nova Scotia.  Flow was from left to right.
<a href="//commons.wikimedia.org/wiki/User:Rygel,_M.C." title="User:Rygel, M.C.">Michael C. Rygel</a>
CC BY 3.0
<span class="int-own-work" lang="en">Own work</span>