Allan W. Eckert
Allan W. Eckert (born 1931) is an American historical novelist and naturalist.
Mesmerian Annals · #1
The Dark Green Tunnel is a fantasy, a la C. S. Lewis, about twins (boy and girl) who find their way into a parallel world in which there are strange creatures, strange people, strange topography, and evil kings and warlocks trying to rule the entire land of Messmeria. The twins join the "good" forces to help overcome the evil ones.