This building is constructed from "river rock" as are a lot of the older buildings and houses in the area. It was readily available and cheap (perhaps not in labor in gathering them).
The are smooth rounded stones and are usually this brownish color, though sometimes they may be gray.
I am fascinated by the art of stone work. It is a lot like working with a picture puzzle in 3 dimensions, and leaves a sort of monument to the worker when it is finished.