Definition of "graystone"

I certainly was not prepared for the cosy nestling valleys that snuggled against the shoulders of the hills; a land where the graystone cottages and farmsteads still prevailed, but where they had taken on something of the softness of their kind in Gloucester and the Cotswolds, and seemed almost like growths of the soil; […] .

1949 January and February, F. G. Roe, “I Saw Three Englands–1”, in Railway Magazine, page 12

Founded almost 50 years ago, it's an imposing graystone structure (formerly a park district office).

2009 January 4, “Letters: Mr. Obama’s Neighborhood”, in New York Times‎

Because graystones were more expensive to build than frame buildings and had a more substantial look and feel, they were the choice of the middle and upper classes.

2017, Terry Moor, Reinventing an Urban Vernacular