Charcoal Ammonites - Almost finished stage 2

Progress continues about as expected on the ammonite fossil.  Today I concentrated on the sandy/grainy section.  I wanted to add more texture as well as definition and form.  I wanted the sandy area to feel look solid.  I'm not 100% sure that I've achieved what I wanted there. I think I may have a bit TOO much form.  I need to consider carefully because my next step is to cover the image with a workable fixative so that I can begin work on the background.

As this image is being done completely in charcoal, I've noticed that when I apply anything to "smudge" into the paper, the opposite happens.  I understand that rubbing should cause some of the medium to "lift" onto whatever you're rubbing with.  It's just that it isn't always the effect I'm going for. So I've had to be extra careful with erasing and brushing excess bits off because that causes a smudge more often than not!