49 Tex.Jur.2d, Reformation of Instruments, Sec. 22, pp. 622, 623; compare National Resort Communities, Inc. v. Cain, 526 S.W.2d 510 (Tex. 1975), and see also Gilbert v. Smith, 49 S.W.2d 702 (Tex.Comm.App. 1932, judgmt. adopted), and Burress v. Byrd, 69 S.W.2d 529 (Tex.Civ.App. Texarkana 1934, writ dism'd). And the mutual mistake which will warrant such reformation may be either that the parties mistakenly believed the description in the contract was legally sufficient, Morrow v. Shotwell, supra; Foster v. Bullard, 496 S.W.2d 724 (Tex.Civ.App. Austin 1973, writ ref'd n.r.e.), or that field notes were intended to be, but were not, attached to the contract either at or after its signing.