Agony of Rock

This is a pastel painting that is causing me grief!!
I'm copying a photo my husband took at Marwell Zoo, but I want to have more realistic rocks than the concrete area the photo was taken in.
I had no idea it would be soooo difficult to make up realistic rocks, this is the 2 nd attempt I wiped the first lot out, which I now regret as they were far better.
So I will soldier on and hope my paper can withstand my continued experimentation.....or if indeed my mind can !!!!!
I feel my sanity gradually eroding away!!!