A quoin is a cornerstone in architecture. Note that one side of the quoin as 3
cobblestone layers and the other has 4.

Cobblestone buildings are one of the unique things about the Rochester, NY area.
The majority of them were built in the years preceding the Civil War. There are
approximately 700-1000 and most of them reside within 65 miles of Rochester.

The simplest definition of a cobblestone defines it by size; it can be held in
one hand and can be either fieldstone or water-rounded. Both are the result of glaciers.

Unfortunately, the only photo that I have of the building is in an album and not very good.
CLICK HERE for a better photo of the entire building. It was built in 1842.