I went walking down by the river the other day and picked up a chunk of white fossil coral from the riverbank. Flipping it over in my hand, I noticed a chunk of black fossil coral embedded in the white coral. It’s a discrete chunk of black stuff; angular, and to my untrained eye it appears to be a different organism than the white stuff. It looks like the white coral grew on top of the chunk of black coral.

Is there a general term for one fossil being embedded in another? I imagine that it would be rather common in marine environments, where coral reefs can grow over seafloor detritus. Of course, there may be the odd example of time travelling poachers using trilobite bullets to kill dinosaurs. I guess I’m talking about something other than amber or tar pits.

Also, is there any way of determining whether this was a case of fresh coral growing over fresh, broken coral or fresh coral growing over old, already fossilized coral?