River Rock anomaly?

[Bugzy99]

I love this section of treasurenet.......I am just learning, but this struck me as I was digging in the riverbank...

 

[bradyboy]

only see a normal but cool river rock
Likely a soft deposit in the rock that was slowly washed away
Nice and fun find
Brady

 

[hvacker]

If I'm right the hole was caused by a smaller rock caught in a eddy current.
Like this but mine has the smaller rock intact.