This book is fantasy to the extent that it is set in a remote period of the Earth's history, and populates it with races of men, and some other creatures, which cannot be precisely identified with any of which remains or fossil impressions have been discovered. It is realism in that the conditions which it presents are logical and credible, and include nothing which may not quite probably have occurred in the immense period during which the human race has existed. But it is primarily an exciting story of adventure and romance.