This is apparently a compositional note, focusing on the general massing of elements and primary tonal contrasts, with some finished work in view. The water in the foreground is therefore the Menai Strait, and the Eagle Tower of the castle dominates the silhouette at the right. It may be based on the studies of Caernarvon Castle that Turner had already made in his contemporary Lancashire and North Wales sketchbook (Tate D01941, D01943, D01945; Turner Bequest XLV 21a, 22a, 23a), though he has here eliminated the dramatic outline of the mountains in the background of the view.
Further thoughts on this subject are on folios 50 verso, 51 recto, 52 recto and 54 recto (D02071, D02072, D02074, D02077), and a further outline sketch of part of the castle is on folio 55 verso (D02080). These ideas for a composition seem to revolve around the motif of the castle seen in silhouette against a strongly luminous sky.
Turner had completed an important watercolour on this theme, Caernarvon Castle (private collection)1 for exhibition at the Royal Academy in the spring of this year, 1799, showing the castle as seen from the east. Similar notes in the Studies for Pictures sketchbook, begun about this time, Tate D03998 and D04102 (Turner Bequest LXIX 5, 88), may also relate to Caernarvon – or possibly to Dunstansburgh and Pembroke Castles, which he was probably considering as alternative subjects. In the event he produced two important watercolours of Pembroke in the first few years of the new century (National Museum Wales, Cardiff; Art Gallery of Ontario, Toronto).2
The bottom right corner has been torn and made up.