If I weren't sure what the walls were made of, I think I go with walls or walling rather than specifying brickwork or stonework. You might also use masonry. The outlines of masonry.

They are identifiable by the outlines of walls.

Pinhoulland has as many as seven houses, a few short traces of walls and many cairns.

Excavations on the remains of the structure. The rectangular inner walls are clearly visible in this picture along with the outline of the circular outer wall.

http://www.orkneyjar.com/archaeology/brodgar.htm

Mauerwerk – stonework, walling