The Floating Islands of Lake Diuturna

In The Sword of the Lictor, Wolfe populates Lake Diuturna with floating islands which move about with the wind. This, I had thought, was another strange and exotic invention that the author used to separate our world from the future Urth. Well, I've been reading Charles Darwin's Voyage of the Beagle, a book I had always meant to read. When Darwin gets to Lake Titicaca high in the Andes, he describes the floating islands in the lake. Looking at Wikipedia, I find that even to this day there are Indians who live on the floating islands. So what I took to be fantastic was simply fact. I wonder if there are more such fantastic realities in TBOTNS. Best wishes, Jack

Oh yeah. I thought everybody knew this. .