Hi Fitz,
>>I would imagine that the use of chalk is simply because of the sheer whiteness of the material.
<<
It only stays white when exposed to the air for a shortish time, I'm in the E Yorks Wolds and any lumps of chalk in the garden surface as a very creamy colour and are only white when they are freshly split. They soon dull and if on damp ground are prone to going green. If ancient sites were chalk-faced for the pure white appearance, they will have had to be cleaned or maybe coated to preserve their appearance. Some of the larger round hilltop mounds here would have looked spectacular with a white covering. I've also often pondered about the earthworks that are serpent-like ridges just under the brows of some hills and their visual impact if they were white. Speaking of which, there's a 5-wide dyke system, that's 5 parallel humps and ditches that originally stretched from Market Weighton to Bridlington, they pass through the chalk uplands, what a sight they'd be if white.
>>Couple all of this with the chalk being the rock that yeilds the best quality flint, then we could be heading towards a sacred geology.<<
There are lots of flint tools found locally displayed in the Hull and East Riding Museum but the best quality ones, and the knapping is superb, weren't from E Yorks, they're from I think Suffolk or Norfolk < don't quote me, ask the museum!> There's an excellent Neolithic display there, apparrently, they have over 44,000 neolithic to BA artefacts. The replicas of the Folkton Drums are fascinating, don't know if they are a unique chalk artefact, the workmanship is superb and it seems they were made from local chalk.
http://antiquity.ac.uk/ProjGall/middleton/
Rune