The Hollow Earth by R.W. Bernard

This is not the original uploaded ebook, unfortunately I'm no longer in possession of the original. Can also be found here in html format:
http://www.ourhollowearth.com/Bernard/Index.htm

The author believes that the truest conception of the structure of the Earth is based on the idea that when it was in a molten state during its formation, centrifugal force caused the heavier substances to be thrown outward, toward its periphery, in the form of rocks and metals, to form its outer crust, leaving its interior hollow, with openings at the poles, where centrifugal force was less and where there was less tendency to throw materials outward, which was greater at the equator, causing the bulging of the earth in this region. It has been estimated that as a result of the Earth's rotation on its axis during its formative state, polar depressions and openings thus formed would measure about 1,400 miles in diameter.

"That enchanted Continent in the Sky, Land of Everlasting Mystery! "

"I'd like to see that land beyond the (North) Pole. That area beyond the Pole is the Center of the Great Unknown:"

- Rear Admiral Richard E. Byrd

The above two statements by the greatest explorer in modern times, Rear Admiral Richard E. Byrd of the United States Navy, cannot be understood nor make any sense according to old geographical theories that the earth is a solid sphere with a fiery core, on which both North and South Poles are fixed points. If such was the case, and if Admiral Byrd flew for 1,700 and 2,300 miles respectively across North and South Poles, to the icy and snowbound lands that lie on the other side, whose geography is fairly well known, it would be incomprehensible for him to make such a statement, referring to this territory on the other side of the Poles as "the great unknown".