From Delineations of Fonthill and its abbey by John Rutter (London: 1823): Sp Coll q63

The ceiling is of oak, reticulated in square panels, placed at some distance from each other, and their intervals filled with meshes of a lozenge form, with bosses at their intersections, and an heraldic emblem on each of the square panels.
An enriched cornice of oak surrounds the room; its frieze has quatre-foils separated by a short range of trefoil-headed apertures or panels; in each quatre-foil is placed an emblazoned shield, surrounded by the garter.
On the west side of the apartment are seven lofty pointed-arch windows, with massive mullions, transoms, and tracery; the lower parts filled with plate, and the upper ones with stained glass, covered with armorial decorations; opposite to six of these windows, and on the other side, are recesses for books, with armoires beneath them; opposite to the middle, and to the seventh one, is the chimney piece, of variegated marble in the gothic style; each end of the gallery is nearly occupied by the arch-ways, which open to the apartments beyond them.
Dimensions 68 ft. long, 16 ft. 10 in. wide, 17 ft. 10 in. high.

(page 36)