Daly, Reginald. Earth's most challenging mysteries. - Grand Rapids, Baker Book House [1972] - 403 p. 21 cm. Bibliography: p. 397-403. ISBN: 0801028175 LCCN: 73168176 Subjects--Geographic Terms: Earth (Planet)--Miscellanea. LC Class. No.: QE53 / .D35 Dewey Class. No.: 550 / D153e