Found walking the River bank.

[ParkersMom]

I've never found rocks like this before. Anybody have any idea on what these could be?

 

[P.ALLEN]

so that is stream weathered Limestone, with either silica(more than likely(silica/chert)) or iron nodules that erode way slower than the limestone, I love finding those. Michigan beaches have a lot of them, you can actually find them all over if Limestone is present in the strata.