Interground

Underground.
Interearth.
Interloam.
Interclay.
Intersand.
Intersilt.

Nothing is under anything, because it's then in an unexistant state. Instead henceforth refer to all that is beneath one as interdenominal. In such cases of earth, it's best to accurately define that bodies in the mortuary are lowered 2 meters interground. As in cases such as the Nazi U-Boat, they were designed as interboats for interwasser advantage to opponents on the surface.