Purple Foxx - yes, that was the book I was talking about. Now I think its full name is "The Democratic Muse ... the folk music revival in Scotland".

As for Ian MacDonald, you get some broader subject matter from his collection of rock/folk/pop journalism "The People's Music", some of which is absolutely brilliant, some of which is not that startling, and the last essay of which (on Nick Drake) feels like a clear signpost that he was about to commit suicide himself.