The Man Who Sold the Earth — John Russell Fearn

Jacob Mastervil, money-master of the world, carefully planned his masterdeal -- the sale of an entire world! But a primeval race of super-scientists, long thought to be vanished from the surface of the Earth, aids Bruce Calthrop in revealing the true identity of the world-seller -- leading to a shocking climax of a battle between the science of an ancient Earth and that of another planet!