  We have studied the structure of inert layer 4He adsorbed on mesoporous
silica (FSM-16), by the vapor pressure and heat capacity measurements. The heat
capacity shows a Schottky-like peak due to the excitation of a part of
localized solid to fluid. We analyzed the heat capacity over a wide temperature
region based on the model including the contribution of the localized solid and
excited fluid and clarified that the excited fluid coexists with the localized
solid at high temperature. As the areal density approaches the value at which
superfluid appears (n_C), the fluid amount is likely to go to zero, suggesting
a possibility that the inert layer is solidified just below n_C.
