Save is a conjunction in this sentence, with the same meaning as except or but. "But/except for a great upheaval ....." would mean the same.

It means "except," and is one of the ordinary dictionary definitions. However, in 2014 it is an old-fashioned use. I have it in my passive vocabulary--I understand it when I read it--but I can't imagine using it. The entire sentence you quote has an old-fashioned sound to it; it is "purple prose." I'm going to Google it and see if I can find where it's from. I'm going to guess that sentence was written sometime between 1850 and 1930. This is interesting--where DID you run across it, Miss Tea? It is from a book by Sir Arthur Conan Doyle, entitled "Sir Nigel," and it was written in 1905. Conan Doyle is famous for his Sherlock Holmes stories, but his other books are pretty obscure. Some other examples of this usage: "All the machinery had gone. Save for the big mound of greyish-blue powder in one corner, certain bars of aluminium in another, the black birds, and the skeletons of the killed, the place was merely an empty circular pit in the sand." --H. G. Wells, The War of the Worlds (1898) But I guess it is still in use: "Save for a few vague quotes about taking arms (some of which fake quotes floating around the internet) the closest the founders discussed about the second amendment were....", "Leaked video shows Sense 6 looks mostly the same, save for a few new features."