Pete, I've just scrolled down the thread you've given above and the 1881 map is impressive to say the least! I wonder if it's been drawn from an earlier illustration by Stukeley? And what's that similar-looking mound at the top of the Sanctuary?
Well thats a bit of an odd map and the Hills are dubious at best.
What is interesting is that it is after the 1849 dig so if Merewether dumped the spoil it May explain the new hill.
The mound by the sanctuary is probably one of the Round barrows on the hill which were a lot larger then.
Notice the Head of the snake has been elongated after stukeleys theory.