Right, can someone tell me what a dry wall means in the excerpt from Edith Wharton's novel Summer below? It can't be the same thing as a modern dry wall that people use indoors when building a house (the book is from 1917).

She sat up, brushed the bits of grass from her hair, and looked down on
the house where she held sway. It stood just below her, cheerless and
untended, its faded red front divided from the road by a "yard" with
a path bordered by gooseberry bushes, a stone well overgrown with
traveller's joy, and a sickly Crimson Rambler tied to a fan-shaped
support, which Mr. Royall had once brought up from Hepburn to please
her. Behind the house a bit of uneven ground with clothes-lines strung
across it stretched up to a dry wall, and beyond the wall a patch of
corn and a few rows of potatoes strayed vaguely into the adjoining
wilderness of rock and fern.

Does it simply mean a wall that is dry? No, not very likely. Probably a wall that is built in some special way, right?