Marks in limestone rock

[Railguy]

What makes Mark's like these in limestone? There r three rows in this three inch limestone.

Thanks for helping railguy

[Innocentx]

That's pretty cool looking. Are you sure it's limestone? It reminds me of chert artifact. Don't know what made those marks but it could be something that was eroded away.

[Railguy]

I don't think it's man made. I'm pretty sure it s limestone but could be wrong. If u broke it i r would be black/,gray inside.white is like a crust that's on the outside.

[Rockwood]

They look like molds of a suture, but I really can't place them.

[GeschWhat]

Those in the 3rd picture look similar to what an impression would look like from the edge of a bivalve.