Displacement reaction

I don't think displacement reaction will occur if a copper rod is put into a beaker of pure mercury.
Although mercury is lower than the copper in reactivity series, the reaction only occur in solution. Displacement reaction is the more reactive metal dissolve and the lower reactive metal ion reduce to become metal solid.
For example, put Fe rod into CuSO4 solution, some reddish brown solid(Cu) occur on the Fe rod. Some bubble occur. Fe slightly dissolve. The solution become colourless.

1. Copper does not easily form amalgam with mercury, so it'll not dissolve.
2. copper (8.96g/cm3) is less dense than mercury (13.5g/cm3), so copper will float on mercury.