These are book covers, from the British Library Collection, of old 19th Century western pulp novels. They are cheap and sensational looking, but they none-the-less must have established a lot of the tropes and cliches used by later western novels and movies.
I've never read one, I think I'll dig around Project Gutenberg and see if they have a few. I'll post about it if I'm successful. Of course there are more covers after the jump.