Samuelson's inscription (spelling correction):

MOTHER TIME
NEITHER WEALTH(,) LAWS NOR ARMYS (ARMIES) CAN STOP THE
HUMAN MIND FROM CREATING NEW OR EMPROVE (IMPROVE) UP ON
THE PRESENT DAY RELIGION AND GOVERMENT (GOVERNMENT).
WATER IS SAFT (SOFT) ONLY HARD IN THE CHEMICALLS (CHEMICALS)
BUT WITH TIME THE OCEAN CAN GRIEND (GRIND) THE HARDEST GRANIT (GRANITE) TO A POWDERED SAND.
SO WITH TIME WILL THE HUMAN RACE GRIEND (GRIND)
OUT ITS OWN DESTINYS (DESTINIES) REGARDLESS OF THE
OPPOSITION OR PARTY IN POWER.

Interpretation:

"Time is an immutable force.  With time the human mind will create new religions and government structures.  Laws can be made against such activities and armies can fight battles to contain the human creative spirit but they will all fail. 

The inevitability of such human driven progress is much like the ocean that can grind the hardest rock into sand given time.  Nothing can stop it.

It is human destiny to constantly create and improve."

Send in your own interpretation.