Sorry I cant really say owt on the megaliths and so on, but,
I actually bought that book when it first came out, the only bit that stayed with me was Wilsons comment .... What ever happened to humanity all those millenia ago was so profound that we're still reeling from the shock of it now, thats not a direct quote, it was years ago when I read it. I took that to mean that people are generally a bit bonkers and unsure what sentience is or what to do with it.
I probably read too many of these way out there books, the first inkling was when I couldnt remember which "fact" was which orthodox or unorthodox,
I decided I hadnt really got time to read either nowadays so I just enjoy a site on face value. (still got respect for Gram Hancock though)