A stone wall n laid one stone thick—also used as a mass noun.
1805 Centinel of Freedom (Newark NJ) 16 July /3 cwMA (as of 1780), It [=a whirlwind] passed a certain piece of ploughed land and took up the dirt to a great height, . . and from the ploughed land, it crossed a single stone wall & threw it down for a considerable distance. 1851 OH Cultivator 7.52, A good builder can lay four rods of double, or with some assistance, as much single wall in a day, thus costing not over 25 cents per rod. 1859 Genesee Farmer 20.213 ME, We build double, half-double, and single wall, without trenching. . . The size of single wall depends upon the size of stone—the largest being laid at the bottom, then the next in size, and so on in regular gradation. 1904 MA Ploughman & New Engl. Jrl. Ag. 17 Sept 2/2 ME, We used everything from the size of a goose egg to a cock of hay. It was largely double wall, though we often build single walls out of large bottoms and a second and third stone top of that.