Raymond W Bernard The Hollow Earth The Greatest Geographical Discovery In History Made By Admiral Richard E. Byrd In The Mysterious Land Beyond The Poles The True Origin Of The Flying Saucers (1964)
“Published in 1964 this unusual book has become a classic. Positive
extraterrestrials, actually our ancestors, come here from all over the
Milky Way Galaxy, and from dimensions of times, yet some of the them are
from the Inner Earth or Agharta. The epoch-making significance of
Admiral Byrd's flight for 2735 kilometers (1700 miles) into the North
Polar opening leading to the hollow interior of the earth, home of
diverse races of advanced humans will startle the world. The author
claims that this extraordinary book proves that there exists on the
inside of the earth's crust, which is about 1237 kilometers (800 miles)
thick a New World, and that Admiral Byrd's polar expeditions penetrated a
total distance of 6437 kilometers (4,000 miles) into this Land Beyond
the North and South Poles, where there exist two huge openings, about
1931 kilometers (1200 miles) in the north pole and a smaller one in the
south both leading to the subterranean world of our planet.”
pdf version here:
https://archive.org/details/raymondwbernardthehollowearththegreatestgeographicaldiscoveryinhistorymadebyadmi 
