I like the Paul Devereaux theories on entoptic representation. It's a theory that makes a lot of sense to me.

I still don't see why a druid is being arrogant in forming theories based on a study of the artworks. No one knows what they mean, so theories are all anyone has. What makes the druid more arrogant than a megalithic enthusiast with a theory, for instance?

I read an article recently about cup and ring mark formations being done by people ingesting stone dust, and hallucinogenic moulds growing on the stones which grew there because of libations of milk being left there. Basically saying they ground out the markings on a vision quest, ingesting the stone dust and mould mix to get high while doing so, and each questor made the marks deeper each time they visited. Didn't have an answer, or even a mention as to how the milk could sit in the marks on vertical slabs though.

No doubt there's dozens more theories on those I've yet to come across too.