armored mud balls
... that armored mud balls are formed underwater when fragments of clay or mud are rolled by moving currents, picking up a coating of gravel or pebbles that helps to stop them breaking down further?
... that <b id="mwew"><a href="./Armored_mud_ball" id="mwfA" rel="mw:WikiLink" title="Armored mud ball">armored mud balls</a></b> are formed underwater when fragments of clay or mud are rolled by moving currents, picking up a coating of gravel or pebbles that helps to stop them breaking down further?