A few post offices in the later 1800s used ovals. Since I collect the 2c Brown stamp canceled by Vermont postmarks, these fit right into that collection
South Shaftsbury was a post office in the Town of Shaftsbury in Bennington County. Shaftsbury was once the home of poet Robert Frost as well as Jacob Merrit Howard, one of the founders of the Republican Party. The South Shaftsbury post office existed from 1831 to 1961.
Both of these ovals have the full name "VERMONT" for the state name rather than VT usually sound on postmarks.