Keith Laumer 
Back to the Time Trap 

A Wall Street trader leaves the bulls and bears – and comes face-to-face with hungrier dinosaurs. A Roaring ’20s gangster gets roughed up – by real cavemen. A pioneer hitches up his covered wagon on the Oregon Trail – and winds up in a modern shopping mall. And Roger Tyson, who thought the space-time continuum had finally settled down to normal, is flung helplessly from the distant past to the far future, and back again.Superbeings from the end of time are struggling for control of the universe with aliens from another galaxy. And if a few random humans get caught in one of their time gates, they don’t much care. So Roger and his friends find themselves facing everyone from the cast of the original Mutiny on the Bounty to real pirates of the Spanish Main in a wild quest to their own time and bring everything back to insanity as usual…