Hmm...interesting. It reminds me of peat inside; but I've never seen fossilized peat. It doesn't look as granular as it did on the outside - more fibrous. Although, it is really hard to tell anything from photos. I wonder if it could be a pile of herbivore coprolite. That would be extremely rare, but very cool IF it is (and that is a BIG if). Herbivore poop rarely fossilizes. Perhaps those are seed hulls and not shells on the outside. Do you have access to a microscope?    @Carlam I ju