This sketch of a loch bordered by mountains is likely to be Loch Katrine at the western end of the Trossachs. The mountain at the far end of the loch is probably Ben A’an as seen from the slopes of Ben Venue. The island is Eilean Molach (or Ellen’s Isle), the setting of Sir Walter Scott’s Lady of the Lake, an edition of which was illustrated with an engraving after Turner’s watercolour Loch Katrine circa 1832 (British Museum).1 There are numerous sketches of Loch Katrine in this sketchbook, for references see folio 47 (D26528).
At the top of the page Turner inscribed a note that appears to read ‘Nol of Glen Finglas’. Glen Finglas lies a few miles to the east of Loch Katrine in the direction that this view is facing. The reference therefore applies to the proximity of the glen, rather than its depiction.
Andrew Wilton, J.M.W. Turner: His Life and Work, Fribourg 1979, p.1084 no.1084.