Brand new to fossils here, and hope I’m following the rules of this forum. I recently collected some rocks from the creek behind my house in for my fish tank. I noticed that one of them has fossilized remains (I’m not sure I’m using the correct terminology here). More specifically, this was collected at (38.8069171, -77.1493230) on the surface of the creek bed in Alexandria, VA. The surrounding rocks were of all colors, shapes, and sizes. I’ve taken a picture and used my unsightly finger for scale. Could anyone inform me of what I’m seeing? I tried some google searches but was admittedly unsure how to search for this. Thank you!