Mu was an immense continent covering nearly one-half of the Pacific Ocean. When she sank during volcanic destruction, fifty million square miles of water claimed her place. This vast continent and culture was the center of civilization some 25,000 years ago. This is the story of Churchward's search for the lost continent, from the vaults of an Indian temple to the four corners of the world.
It also includes offensive gems such as "The bushman of Northern Australia are probably the lowest type of humanity on earth, lower than the ordinary forest beasts.". All the while concocting an absurd theory that white civilisation came from an immense continent in the middle of the pacific ocean, that just vanished in a disaster leaving only the pacific islands behind. As for why there's no tangible evidence of such? People devolved he claimed, and only the dregs really survived to begin with.
As far as absurd early 20th century books go, you're on a winner with this if that's what you're after, but for actual factual information you'll be looking in the wrong place if you pick this up, it belongs in the fiction category more than it does non fiction.