Sure. 1 is the pressure for a solid (your sack/head example), 2 is the pressure for a gas (the OP situation).There may be two kinds of pressure:-
1. Defined by you as the contact force.
2. Pressure due to collision of molecules with the walls of container that we use in thermodynamics . So the air above the slab must be colliding with our slab and hence may be causing some collisional pressure.
What is the question?