Not on display
The two sketches, drawn with the sketchbook inverted above and below the main sketch on this page, are certainly (as David Wallace-Hadrill and Janet Carolan have identified) depictions of Duart Castle.1 Both are from the east, and were made from the deck of a steamboat in the Firth of Lorne as it headed for the entrance to the Sound of Mull. In these rapid and roughly executed sketches Turner has tried to capture the general shape of the castle and its main architectural details such as the roofs. The smaller sketch at the fore-edge of the page includes a faint outline of the hills of Mull beyond the castle, and the larger sketch towards the page gutter includes the outline of a hill to the right, perhaps Maol Nan Uan.
The main sketch on this page, drawn with the sketchbook inverted from the other sketches, does not look like Duart Castle. It is too narrow, has a pointed roof and sits on a rock with cliffs behind it, rather than on a large promontory. Turner’s boat would have passed Dunollie Castle shortly after leaving Oban, so this is a possibility. There are several sketches in the Staffa sketchbook which show the castle from the west (Tate D26852; Turner Bequest CCLXXIII 57) which bear a slight, though not great resemblance to this sketch. Another possibility is Aros Castle, which is depicted on folio 10 verso and the inside back cover (D26954, D41020). Turner also made a very similar looking sketch in the Staffa sketchbook (Tate D26957; Turner Bequest CCLXXV 2).
David Wallace-Hadrill and Janet Carolan, ‘Turner on the Isle of Skye 1831’, [circa 1991], Tate catalogue files, [folios 5, 29].