I've read a number of books and articles about Stonehenge, and so far they surprise me in their ignorance of geology. I mean the kind of geology one would learn in two semesters of college.

"Bluestones". There is no rock unit called a bluestone. This term is used for gray rocks at Stonehenge. They could be different rock types and could have come from different places.

"Sarsen". This word means foreign and applies to rocks that don't look like they belong in the place where they are seen. Again, they could have come from many different places.

I have yet to see a book address the possibility that the big stones of Stonehenge are glacial erratics. Where I live, we occasionally find boulders of Sioux quartzite as big as automobiles which have been moved over 300 miles by the glaciers. If they are really big, they are so hard to get rid of that people just mount a plaque on them and deem them a historic monument.