"lay prone" is a correct and usable phrase in written English.
It can be used to describe a person or object lying flat on their stomach. Example sentence: The victim lay prone on the ground, barely moving.
Monica lay prone and exhausted on a battered sofa.
Sylvain Marveaux lay prone in the penalty area with cramp.
The boy lay prone in the grass, his chin resting on his hands.
Once LaCouture scored, however, Cechmanek lay prone with his face on the ice for several seconds.
Instead, he ignored the penalty shout as Drogba lay prone in disbelief.
The surfers lay prone on their boards until a wave rolled in and swept them away.
In due course, Williams knocked out Carlton's half-forward, Ken Hands, who lay prone behind play.
Some victims lay prone on bare ground in convulsions, physicians recalled.
He briefly lay prone on the ice before skating off without assistance.
He lay prone on his breast, and gradually his legs fused together.
Artur Moraes, the Benfica goalie, lay prone on the grass, deflated by disappointment.
