Large Nodules Near Aquia Creek Va (Potomac River)

[esword]

Newbie question (because it's hard to search google for "What the heck are these?") - I have seen these before, but never so many right next to each other.

Some are just tubes and then some have a rounded top:

Nearby I also found this, which looks a lot like the end of a femur, but it just doesn't feel like a fossil:

Sorry for the odd pictures in hand, but it was the best way to give the "3d" perspective for how round it is and how the end looks sheared off. I thought it may just be a smoothed out version of the other things I saw above, but those are all hollow in the middle while this is quite solid.

Thanks for helping a noob,

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[njfossilhunter]

Welcome to the forum....I have hunted the Potomac river for a long time...Mostly the Virginia portion,, and I don't recall ever coming across these concretions before,,if that's what they are. Where about did you find them..sometimes the location can help with the ID..knowing the geological formations also helps. Did they come out of the Aquia formation.

Edited August 8, 2015 by njfossilhunter

[Auspex]

They occur locally, in certain strata. I believe nucleated around roots.

[PA Fossil Finder]

They occur locally, in certain strata. I believe nucleated around roots.

I'm pretty sure those are called rhizoliths.

[esword]

Thanks, PA - I think rhizolith is the winner. I couldn't find any direct references to rhizoliths and the Aquia formation (or the potomac or mid-atlantic or anything else that came to mind), but it makes sense. They are always hollow and either tubelike or capped at one end. Also very crumbly.

njfossilhunter - Given that I found them near Aquia creek along the Potomac, I'm going to assume they are from the formation of the same name, but that's right around the boundary where things shift around (I forget what formation is to the south, Yorktown maybe?) so I can't say for sure.

Anyone have thoughts on the other pictures I posted - the thing that looks like a femur ball joint? It is solid all the way through and isn't as crumbly as the rhizoliths,

[Auspex]

...Anyone have thoughts on the other pictures I posted - the thing that looks like a femur ball joint? It is solid all the way through and isn't as crumbly as the rhizoliths,

That too is a concretion. It, and the rhizoliths, were formed well after the time of sediment deposition.