Odd one this. I've read a few ERB books and almost the first half of this is a series of wartime encounters involving a U boat! The bit I was looking forward to came later, and seemed a bit rushed and little simplified. Hordes of dinosaurs but the author gets fed up with going into detail about them. The landscape is good though the scale of it is hard to believe if it is a lost world, and the stratification of the cavemen is fascinating though doesn't get explained in this book. I will read the two follow ups eagerly though, at least to try and solve the mysteries left by this one.
Intriguing yarn. I saw a modern film version some time ago but the original narrative is so much better, if somewhat far fetched. That is what a tale is all about. Bought some more by the same author, 19th century fantasy.