“ It was a common feature of socage tenure and came in course of time to designate any fixed rent due from a socage tenant. Quit rents were protected from abolition by the provisions of the Statute of Military Tenures. It is probable, however, that they have become entirely obsolete in the United States, excepting in Pennsylvania, where they survive to a limited extent, though there is no legal objection to their survival elsewhere in the States formerly subject to socage tenure. ”